- #666
Al Johnson
- 7
- 0
Many thanks for additional explanations :-)
Race car suspension Class
- Automotive
- Thread starter Ranger Mike
- Start date
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- Tags
- Car Class Race Suspension
In summary,-The stock car suspension is important for understanding the complexity of a Formula Cars suspension.-When designing a (front) suspension, geometry layout is critical.-spindle choice and dimensions, kingpin and steering inclination, wheel offset, frame height, car track width, camber change curve, static roll center height and location and roll axis location are major factors.-The first critical thing to do is to establish the roll center height and lateral location. The roll center is established by fixed points and angles of the A-arms. These pivot points and angles also establish the camber gain and bump steer.-I have used Suspension Analyzer for years on Super late Model stock cars as
- #667
- 2,337
- 351
The Racing Line
http://www.drivingfast.net/techniques/racing-line.htm
Good article on like says it better than I can. I borrowed A Majority of it and added some on particulars of oval track racing on pavement.
There recently was a request to assist a poster on Physics Forum on calculating the path of a car in a turn. I pointed out the fact that it isn't that simple and you can not fit a static model into a kinematic environment. Even if you can get to thinking in 3-D you have to add in many variables and no amount of math is going to tell you where the car will be in a turn. For one thing you have a human driving and we all know how flakey those carbon units are!
Lets look at a right hand turn ( I know.. it’s a British thing, Billy Bob) oval track. The racing line is THE fastest path you are able to go thru a particular corner. In fact if you had an overhead view of an oval race track and mapped the cars location you would see a diamond pattern and not an oval pattern. The driver follows this racing line to take corners in the fastest possible manner. The idea is to find the best line with minimum turning effort and use the track banking to your advantage to shoot down through the corner for max speed. This line WILL Change, daily and most of the time hourly because of sunlight, temperatures, rubber build up on the track, diminishing tire grip and other factors.
How do you find the best line? You walk the track. You have to do the mental drill of looking for the Apex and figure out the best way to hit it. Once the Apex is found you find the braking point, turn in point and power on point of exit. You have to remember all these will change as the car and track conditions change.
Finding the Apex - The apex is the point at which you are closest to the inside of the corner, also referred to as the clipping point. Once you have hit the apex you should be able to reduce the steering lock and increase the throttle. There are two different types of apex, the geometrical apex and the racing apex. The geometric apex of a constant radius corner is the central point on the inside and this may also be the racing apex.
The traditional or geometric racing line
To carry maximum speed through a corner, you need to take the straightest line through the corner to minimize cornering force and keep up maximum speed. This route tends to use the geometric apex of the corner and is usually known as the classic racing line. Note the Apex location in the diagram . We have a constant radius 90 degree right hander and the geometric apex is exactly half way around the corner. This Apex will usually get you close to the fastest time but your car’s tire grip may dictate you needing to move the apex for max speed. More on this later.
The Braking Point – All drivers mentally mark the Bare Point, Turn In Point and Power on point when hot lapping. It is a constant process of finding the best line through that one turn and “hitting the marks” time after time. That is one reason the retaining walls are painted and marked before the apex. So you are bombing down the front chute to Turn One and hit the brakes...Wrong! You better have more finesse that that and you better have your Brake Bias cranked into where you don’t swap ends when you hit the Whoa pedal. Losing 50 MPH speed should be a controlled process. Threshold braking is the technique where you are on the brakes the most you can apply and still not locking up the wheels. You are on the binders doing maximum braking when you are in a straight line.
So how do you find the Braking Point for each corner? You shoot for the apex and begin braking early. As you learn each corner you begin braking later and later until you find the best braking point. IMPORTANT - You are on the binders doing maximum braking when you are in a straight line. You lighten up the pressure but still keep tension on the pedal when in the corner. This does two things. It assists turn in and sets the chassis. This is known as trail braking and is a proven technique to reduce under steer.
Turn In Point - Just like the Braking Point , you have to find the best Turn In point to get the line right. Hit it too late and you'll miss the apex, hit it too soon and you'll have to tighten your line mid corner. Get it right and you'll have a good racing line.
Power On Point – Once you have completed the turn and the car is close to being pointed straight you can get on t he GO pedal. No, we don’t nail the throttle and spin the tires! Finesse again. Learn to give it he gas without tire spin. This point will change as with the other points with tire grip and track conditions. You may have to shift the Apex to a later Apex to get the fastest time. What you want is to transition the turn and get the car hooked up with power on as quick as possible. See diagram. It is better to take a late apex, straighten the car out early and get the power on for a higher exit speed. One final note. If you hit the Apex too early you will cross up the car and miss your best Power On point and have a bad lap time.
Bottom line is the path around the race track is not a perfect oval..far from it and it is not consistent.
http://www.drivingfast.net/techniques/racing-line.htm
Good article on like says it better than I can. I borrowed A Majority of it and added some on particulars of oval track racing on pavement.
There recently was a request to assist a poster on Physics Forum on calculating the path of a car in a turn. I pointed out the fact that it isn't that simple and you can not fit a static model into a kinematic environment. Even if you can get to thinking in 3-D you have to add in many variables and no amount of math is going to tell you where the car will be in a turn. For one thing you have a human driving and we all know how flakey those carbon units are!
Lets look at a right hand turn ( I know.. it’s a British thing, Billy Bob) oval track. The racing line is THE fastest path you are able to go thru a particular corner. In fact if you had an overhead view of an oval race track and mapped the cars location you would see a diamond pattern and not an oval pattern. The driver follows this racing line to take corners in the fastest possible manner. The idea is to find the best line with minimum turning effort and use the track banking to your advantage to shoot down through the corner for max speed. This line WILL Change, daily and most of the time hourly because of sunlight, temperatures, rubber build up on the track, diminishing tire grip and other factors.
How do you find the best line? You walk the track. You have to do the mental drill of looking for the Apex and figure out the best way to hit it. Once the Apex is found you find the braking point, turn in point and power on point of exit. You have to remember all these will change as the car and track conditions change.
Finding the Apex - The apex is the point at which you are closest to the inside of the corner, also referred to as the clipping point. Once you have hit the apex you should be able to reduce the steering lock and increase the throttle. There are two different types of apex, the geometrical apex and the racing apex. The geometric apex of a constant radius corner is the central point on the inside and this may also be the racing apex.
The traditional or geometric racing line
To carry maximum speed through a corner, you need to take the straightest line through the corner to minimize cornering force and keep up maximum speed. This route tends to use the geometric apex of the corner and is usually known as the classic racing line. Note the Apex location in the diagram . We have a constant radius 90 degree right hander and the geometric apex is exactly half way around the corner. This Apex will usually get you close to the fastest time but your car’s tire grip may dictate you needing to move the apex for max speed. More on this later.
The Braking Point – All drivers mentally mark the Bare Point, Turn In Point and Power on point when hot lapping. It is a constant process of finding the best line through that one turn and “hitting the marks” time after time. That is one reason the retaining walls are painted and marked before the apex. So you are bombing down the front chute to Turn One and hit the brakes...Wrong! You better have more finesse that that and you better have your Brake Bias cranked into where you don’t swap ends when you hit the Whoa pedal. Losing 50 MPH speed should be a controlled process. Threshold braking is the technique where you are on the brakes the most you can apply and still not locking up the wheels. You are on the binders doing maximum braking when you are in a straight line.
So how do you find the Braking Point for each corner? You shoot for the apex and begin braking early. As you learn each corner you begin braking later and later until you find the best braking point. IMPORTANT - You are on the binders doing maximum braking when you are in a straight line. You lighten up the pressure but still keep tension on the pedal when in the corner. This does two things. It assists turn in and sets the chassis. This is known as trail braking and is a proven technique to reduce under steer.
Turn In Point - Just like the Braking Point , you have to find the best Turn In point to get the line right. Hit it too late and you'll miss the apex, hit it too soon and you'll have to tighten your line mid corner. Get it right and you'll have a good racing line.
Power On Point – Once you have completed the turn and the car is close to being pointed straight you can get on t he GO pedal. No, we don’t nail the throttle and spin the tires! Finesse again. Learn to give it he gas without tire spin. This point will change as with the other points with tire grip and track conditions. You may have to shift the Apex to a later Apex to get the fastest time. What you want is to transition the turn and get the car hooked up with power on as quick as possible. See diagram. It is better to take a late apex, straighten the car out early and get the power on for a higher exit speed. One final note. If you hit the Apex too early you will cross up the car and miss your best Power On point and have a bad lap time.
Bottom line is the path around the race track is not a perfect oval..far from it and it is not consistent.
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- #668
roadkillracing
- 1
- 0
have you ever discussed road race 3 link rear suspension setup and tuning?
- #669
- 2,337
- 351
welcome roadkillracing..we discussed a three link tune in on round track racing but not road course. This begs the point of figuring out how many left and right turns you have on each track and dialing in bias for one particular side. I think the basic set up of being neutral works best. Then adding in or removing various link angles etc.. to add bite or take away traction.
see post 235 on page 16
261 page 17
top link post 81 page 6
rear steer post 116 page 8
what kind of race car are you racing?
see post 235 on page 16
261 page 17
top link post 81 page 6
rear steer post 116 page 8
what kind of race car are you racing?
- #670
radracr
- 30
- 0
Ranger Mike,
We ran our first race of the year after setting up the RC. I have to say - I'm disappointed. I really expected the front tires to shred the track. The feedback from the steering wheel was smoother but the car did not feel like it would take too much 'wheel'. (I felt like the steering wheel was 'free', if that makes sense.) We re-measured the control arm angles and they are all different from our starting point but the RC is at 3.6H, 2.2R. (The lowers had 2* more and the uppers had 5* more meaning the front was lower overall.)
The car started off loose in/off so we put MANY rounds in the LR and took MANY rounds out of the RR. This in turn appears to have upset the front frame heights - the LR rose 1/4" while the RF fell 1/4" leaving the LF a tick higher than the RF. In the end the car ended up tight in (1of5), and loose off (3of5) and pushy at the apex (1of5). We also went with higher rebound shocks which seemed to help the weight transfer.
The tires themselves were older tires from last year.
Unfortunately we were fighting other issues and did not take tire temps.
We ran our first race of the year after setting up the RC. I have to say - I'm disappointed. I really expected the front tires to shred the track. The feedback from the steering wheel was smoother but the car did not feel like it would take too much 'wheel'. (I felt like the steering wheel was 'free', if that makes sense.) We re-measured the control arm angles and they are all different from our starting point but the RC is at 3.6H, 2.2R. (The lowers had 2* more and the uppers had 5* more meaning the front was lower overall.)
The car started off loose in/off so we put MANY rounds in the LR and took MANY rounds out of the RR. This in turn appears to have upset the front frame heights - the LR rose 1/4" while the RF fell 1/4" leaving the LF a tick higher than the RF. In the end the car ended up tight in (1of5), and loose off (3of5) and pushy at the apex (1of5). We also went with higher rebound shocks which seemed to help the weight transfer.
The tires themselves were older tires from last year.
Unfortunately we were fighting other issues and did not take tire temps.
- #671
- 2,337
- 351
radracer..
been there ..it is frustrating...but..on the positive side
last year you said the car had a lot of roll like a gorilla had a long lever on the car.
I take it this has improved?
It is better being loose going in and coming out then pushing going in, loose off.
Floaty feel of the wheel means rt front not getting enough weight to plant and turn the car. This means your set up is getting real close to a good set up.
Adding wedge at the track tightened up but not the answer. Basically makes the car a three legged stool. Can you lower the rear roll center?
Sounds like the front RC is performing as should be.
I assume you still have 3270 pound car.
what springs did you end up running? 750 LF 850 RF?
are the spring new or got a lot of racing on them? Old springs will mean your end of race setup will be sagging more than when you dialed it in on garage floor.
been there ..it is frustrating...but..on the positive side
last year you said the car had a lot of roll like a gorilla had a long lever on the car.
I take it this has improved?
It is better being loose going in and coming out then pushing going in, loose off.
Floaty feel of the wheel means rt front not getting enough weight to plant and turn the car. This means your set up is getting real close to a good set up.
Adding wedge at the track tightened up but not the answer. Basically makes the car a three legged stool. Can you lower the rear roll center?
Sounds like the front RC is performing as should be.
I assume you still have 3270 pound car.
what springs did you end up running? 750 LF 850 RF?
are the spring new or got a lot of racing on them? Old springs will mean your end of race setup will be sagging more than when you dialed it in on garage floor.
- #672
radracr
- 30
- 0
It does not appear to be rolling over as much as it did last year. So yes, that has improved.
3297# (full of 22 gallons of fuel.)
Left = 55.9 (versus MAX 56.0)
Rear = 46.1 (versus MAX 47.5)
Cross = 46.5 (after race. Most of the day it was in the 45s. We put many rounds in/out before the race.)
We did end up moving the motor back 3/4" and to the left 5/8" which allowed us to take off 25# of ballast. When we went across the scales with all ballast we had 56.1 LEFT so we had to remove 25# and ended up with 55.9. whew...I was given a nice little "I'm not going to make a big deal of that but you better fix that" speech from the official after the heat race.
RF = 950#
LF = 800#
We went with those as it placed us close to the ideal natural spring frequencies (which I appear to be caught up in.!)
I believe the RF is new while the LF is an older spring that was not used that much.
We can lower the rear RC by taking equal rounds out of each side but since it's a stock 4-link 8.5" corporate 10-bolt it will end up being what it is = 17.0" (I think.) The only other option is to use offset bushings on the upper arms at the rearend.
3297# (full of 22 gallons of fuel.)
Left = 55.9 (versus MAX 56.0)
Rear = 46.1 (versus MAX 47.5)
Cross = 46.5 (after race. Most of the day it was in the 45s. We put many rounds in/out before the race.)
We did end up moving the motor back 3/4" and to the left 5/8" which allowed us to take off 25# of ballast. When we went across the scales with all ballast we had 56.1 LEFT so we had to remove 25# and ended up with 55.9. whew...I was given a nice little "I'm not going to make a big deal of that but you better fix that" speech from the official after the heat race.
RF = 950#
LF = 800#
We went with those as it placed us close to the ideal natural spring frequencies (which I appear to be caught up in.!)
I believe the RF is new while the LF is an older spring that was not used that much.
We can lower the rear RC by taking equal rounds out of each side but since it's a stock 4-link 8.5" corporate 10-bolt it will end up being what it is = 17.0" (I think.) The only other option is to use offset bushings on the upper arms at the rearend.
- #673
- 2,337
- 351
strictly speaking..by the book..a 3200 pound car should run
1050 RF
1000 LF
225 RR
250 LR
springs with 220# sway bar..
every tuning tip at the track says when you are loose going in or mid turn got to stiffer spring in RF
you are running a 100# heavier car
with 950 RF
800 LF springs
I would guess weight is coming forward and staying on the LF side so the car is pivoting on the LF not the RF that is only along for the ride going into the turn. When weight stays on the LF it is not slinging over thru the RC to plant the RF, hence the floaty feeling, RF not getting enough grip ( down force).
The weight is not transferring to the rear (RF specifically) under acceleration and is fish tailing off the turn. As a minimum you need to stiffen up the LF to throw the weight to the RF and RR. It will take a tune and test day to sort out the front springs. It is your call to swap in the “ book” springs or put a 900# in the LF and be prepared to swap in stiffer springs as the stop watch h dictates.
1050 RF
1000 LF
225 RR
250 LR
springs with 220# sway bar..
every tuning tip at the track says when you are loose going in or mid turn got to stiffer spring in RF
you are running a 100# heavier car
with 950 RF
800 LF springs
I would guess weight is coming forward and staying on the LF side so the car is pivoting on the LF not the RF that is only along for the ride going into the turn. When weight stays on the LF it is not slinging over thru the RC to plant the RF, hence the floaty feeling, RF not getting enough grip ( down force).
The weight is not transferring to the rear (RF specifically) under acceleration and is fish tailing off the turn. As a minimum you need to stiffen up the LF to throw the weight to the RF and RR. It will take a tune and test day to sort out the front springs. It is your call to swap in the “ book” springs or put a 900# in the LF and be prepared to swap in stiffer springs as the stop watch h dictates.
- #674
radracr
- 30
- 0
Looking at and comparing the LF tire to the RF - the LF certainly does look like it is working harder. The LF tire appears to be scrubbing more so than the RF - real gooey and lots of rocks. Or to put it a different way, the RF isn't showing near the amount of wear as the LF - no rocks are sticking to the RF.
But you do have me confused. The track tuning tips say stiffer RF but you're proposing stiffer LF.
By the way, the 'book' RF spring is very close to the natural frequency for my set up. (At least that's what the software is telling me.) I'll have to run the numbers for the LF. I don't have my notes by I believe I run a 200# LR and a 175# RR.
Thanks for the feedback!
wow...what a lesson...
But you do have me confused. The track tuning tips say stiffer RF but you're proposing stiffer LF.
By the way, the 'book' RF spring is very close to the natural frequency for my set up. (At least that's what the software is telling me.) I'll have to run the numbers for the LF. I don't have my notes by I believe I run a 200# LR and a 175# RR.
Thanks for the feedback!
wow...what a lesson...
- #675
radracr
- 30
- 0
Sorry, Ranger Mike. I had to think it through. Since my car is loose on EXIT, and not transferring weight to the right side THAT's why I need to stiffen the LF. (Versus loose-in and at apex = stiffer RF, which is not me.)
Got it!
Grasshopper getting wiser...and soon...faster!...
Got it!
Grasshopper getting wiser...and soon...faster!...
- #676
- 2,337
- 351
visulaizing the gorilla
Here we have a real life teaching point. The problem is we have a “ new set up race car” that has ill handling. The question is ..why is it over steering on turn in, apex and exit?
The big gorilla in the room is “ sprung weight”. Everyone hates UNSPRUNG weight because it can not be controlled. That’s why racers mount shocks ( dampers) upside down to reduce the unspring weight by a miniscule amount. Sprung weight can be “ controlled” ( he said laughingly) with shocks and springs and ARB (sway bars). Step one in answering the above question is to find out how much sprung weight we have and determine where it is going.
If we look at Radracers car specs we have a 3300# car with 112 wheelbase. We assume a Center of Gravity height of where the camshaft is above ground and use 16 inch as CG height.
I assume a 66 inch rack width. I am using a figure of 1.15Gs as he has spec tires and a fairly flat track. (If you look up on this post on page 33 post 589 we can get details in depth on theses calculations.)
1. The total amount of weight that is being transferred during cornering
Tw= Gs' x car weight x CGh / track width
1.15Gs x 3300 x 16 / 66 = 920 total pounds transferred during cornering.
Weight Forward = Gs x car weight x CGh / Wheel base
WF = 1.15 x 3300 x 16 / 112 = or 542 pounds transfer to the front of the car.
Total weight transferred= 920# minus 542 # weight transferred forward= 378# weight going to the right side.
So we have about 1/3 of the car weight being slung around during cornering,
16% coming forward and 11% coming over to the right side of the car.
Polar Moment- this is the point where the chassis will move zero amount during weight transfer.
If we take the 112 wheelbase and multiply it by the 46% rear weight we get 112 x 46%= 51.52 inch ,call this 52 inch.
This is one point on the polar moment grid. Next multiply the 66 inch track width by 56% left side weight to find 36.96” call this 37”.
Lastly add 16” height for the CG.
As a check you can take the floor jack and place it 52 inch forward of the rear wheel center.
Move the jack to a point 37” toward the right side from the left tire centerline. This is your polar moment.
You should be able to jack up the car and not have it tilt one way or the other.
As with throwing a baseball, the outside of the ball moves more than the center point of the ball.
This is the point the chassis will move least during cornering.
Visualize the Gorilla - Imagine you have a giant Tupperware tub with a lid.
It is similar to the one your wife uses for that lame meatloaf you hate (never seems to go away,stays years in the fridge).
This tub is 66 inch wide and 112 inch long, is half full of water and weighs 920 pounds.
The lid is sealed so the water won't slosh out.
If we place the tub on the polar moment pivot point it will not balance because there are no springs to SUSPEND the weight.
Gravity will make it flop forward and to the left because the pivot point is offset to the front and to the left. If we were to place 4 x 4 wood blocks of equal height under each corner of the Tupperware tub, (forget the polar moment pivot point for a minute) and scale it, the weight scales would read close to the corner weights of our race car but slightly less because we are measuring sprung weight only. The unsprung weight is not added in. Let's add springs and go racing.
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The left front spring is too soft and goes into coil bind. Most of the water coming forward heads to the left front and stays there.
The water sloshing to the right comes over to the right side of the tub and since the right rear spring is too stiff,
the water sloshes against the tub wall and the right rear tire gives way and the car over steers ( gets loose).
The driver manages to cross arm it thru the apex and gets on the gas pedal to exit and has nothing but wheel spin.
All the water that came forward to the left front is still there. The weak spring did not rebound like we want.
making the car nose heavy so the right rear has no weight for traction. Loose in loose out.
Ideally what we want is to properly handle the sprung weight coming forward and to the right as well as the
RATE it transfers ( better left to another discussion on shocks (dampers)).
Back to our imaginary race car with ideal set up. We go bombing down the straight hit the brakes on corner entry. The water comes forward and hits the left front spring. The spring is stiff enough to take the weight and spring it over to the right side. Since this motion goes through the front roll center it loads the right front tire. The right front spring is dealing with weight coming forward and this additional weight coming from the left side and weigh coming from the left rear (cross weight). We have discuss how down force adds grip on a tire in previous posts. Suffice it to say that now that we have the weight coming from the left front through the front roll center we have the required amount of down force to plant the right front tire and steer the car through the turn. Since the left front spring is of proper spring rate the left front of the car is coming up thru the apex and is putting more weight on the right rear as it continues through the turn toward exit. Meanwhile the right front is done doing it s thing and is moving back to ride height throwing weight to the right rear and left rear. Normally the left rear would be unloaded and “light” but we have wedged the car with cross weight forcing the left rear to dig in on corner exit.
So the question a rises, “Why can’t I directly calculate the exact spring package required for this scenario”?
The polar moment is a static calculation. If we were to draw a line from the front roll center to the rear roll center it would not be parallel with the car center line.
We need exact measurement of the ROLL AXIS as well as true CoG. We have many things impacting on the dynamics and
unless we want to spend a lot of computer time , I recommend getting the spring package close and spend time at tune and test.
At that point the tire temperatures will tell all. Shoot for left ft temp 10 % cooler than rt ft and rear temp 10% cooler than ft temp.
Anyway that’s about as best as I can explain it and I’m out of beer.
Here we have a real life teaching point. The problem is we have a “ new set up race car” that has ill handling. The question is ..why is it over steering on turn in, apex and exit?
The big gorilla in the room is “ sprung weight”. Everyone hates UNSPRUNG weight because it can not be controlled. That’s why racers mount shocks ( dampers) upside down to reduce the unspring weight by a miniscule amount. Sprung weight can be “ controlled” ( he said laughingly) with shocks and springs and ARB (sway bars). Step one in answering the above question is to find out how much sprung weight we have and determine where it is going.
If we look at Radracers car specs we have a 3300# car with 112 wheelbase. We assume a Center of Gravity height of where the camshaft is above ground and use 16 inch as CG height.
I assume a 66 inch rack width. I am using a figure of 1.15Gs as he has spec tires and a fairly flat track. (If you look up on this post on page 33 post 589 we can get details in depth on theses calculations.)
1. The total amount of weight that is being transferred during cornering
Tw= Gs' x car weight x CGh / track width
1.15Gs x 3300 x 16 / 66 = 920 total pounds transferred during cornering.
Weight Forward = Gs x car weight x CGh / Wheel base
WF = 1.15 x 3300 x 16 / 112 = or 542 pounds transfer to the front of the car.
Total weight transferred= 920# minus 542 # weight transferred forward= 378# weight going to the right side.
So we have about 1/3 of the car weight being slung around during cornering,
16% coming forward and 11% coming over to the right side of the car.
Polar Moment- this is the point where the chassis will move zero amount during weight transfer.
If we take the 112 wheelbase and multiply it by the 46% rear weight we get 112 x 46%= 51.52 inch ,call this 52 inch.
This is one point on the polar moment grid. Next multiply the 66 inch track width by 56% left side weight to find 36.96” call this 37”.
Lastly add 16” height for the CG.
As a check you can take the floor jack and place it 52 inch forward of the rear wheel center.
Move the jack to a point 37” toward the right side from the left tire centerline. This is your polar moment.
You should be able to jack up the car and not have it tilt one way or the other.
As with throwing a baseball, the outside of the ball moves more than the center point of the ball.
This is the point the chassis will move least during cornering.
Visualize the Gorilla - Imagine you have a giant Tupperware tub with a lid.
It is similar to the one your wife uses for that lame meatloaf you hate (never seems to go away,stays years in the fridge).
This tub is 66 inch wide and 112 inch long, is half full of water and weighs 920 pounds.
The lid is sealed so the water won't slosh out.
If we place the tub on the polar moment pivot point it will not balance because there are no springs to SUSPEND the weight.
Gravity will make it flop forward and to the left because the pivot point is offset to the front and to the left. If we were to place 4 x 4 wood blocks of equal height under each corner of the Tupperware tub, (forget the polar moment pivot point for a minute) and scale it, the weight scales would read close to the corner weights of our race car but slightly less because we are measuring sprung weight only. The unsprung weight is not added in. Let's add springs and go racing.
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The left front spring is too soft and goes into coil bind. Most of the water coming forward heads to the left front and stays there.
The water sloshing to the right comes over to the right side of the tub and since the right rear spring is too stiff,
the water sloshes against the tub wall and the right rear tire gives way and the car over steers ( gets loose).
The driver manages to cross arm it thru the apex and gets on the gas pedal to exit and has nothing but wheel spin.
All the water that came forward to the left front is still there. The weak spring did not rebound like we want.
making the car nose heavy so the right rear has no weight for traction. Loose in loose out.
Ideally what we want is to properly handle the sprung weight coming forward and to the right as well as the
RATE it transfers ( better left to another discussion on shocks (dampers)).
Back to our imaginary race car with ideal set up. We go bombing down the straight hit the brakes on corner entry. The water comes forward and hits the left front spring. The spring is stiff enough to take the weight and spring it over to the right side. Since this motion goes through the front roll center it loads the right front tire. The right front spring is dealing with weight coming forward and this additional weight coming from the left side and weigh coming from the left rear (cross weight). We have discuss how down force adds grip on a tire in previous posts. Suffice it to say that now that we have the weight coming from the left front through the front roll center we have the required amount of down force to plant the right front tire and steer the car through the turn. Since the left front spring is of proper spring rate the left front of the car is coming up thru the apex and is putting more weight on the right rear as it continues through the turn toward exit. Meanwhile the right front is done doing it s thing and is moving back to ride height throwing weight to the right rear and left rear. Normally the left rear would be unloaded and “light” but we have wedged the car with cross weight forcing the left rear to dig in on corner exit.
So the question a rises, “Why can’t I directly calculate the exact spring package required for this scenario”?
The polar moment is a static calculation. If we were to draw a line from the front roll center to the rear roll center it would not be parallel with the car center line.
We need exact measurement of the ROLL AXIS as well as true CoG. We have many things impacting on the dynamics and
unless we want to spend a lot of computer time , I recommend getting the spring package close and spend time at tune and test.
At that point the tire temperatures will tell all. Shoot for left ft temp 10 % cooler than rt ft and rear temp 10% cooler than ft temp.
Anyway that’s about as best as I can explain it and I’m out of beer.
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So what is happening when we have sever under steer at corner entry. AKA pushing like a freight train going in..
This condition is caused by the front suspensions inability to handle the weight transferred. Under steer can be caused by improper tire inflation,
wrong camber curve, brake bias is wrong, cross weight, stagger, roll center location, but most common is improper spring rates.
Scenario 1- too soft a rt ft spring
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The right front spring is too soft and goes into coil bind. A majority of the water coming forward heads to the right front and stays there.
The water sloshing to the right comes over to the right side of the tub and since the right rear spring is too soft,
the water sloshes against the tub wall and the right rear tire really digs in because of all the added weight.
The car will not steer as the right front tire is being scrubbed sideways, the tire literally is shredded as the car heads to the outside guard rail. Sever push.
At this point the driver has to back off the throttle and moose it around the apex until he can get back on the gas pedal.
Scenario 2 – too stiff a rt ft spring
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The right front spring is too stiff. We have the typical go kart situation. The water coming forward heads to the right front and is kicked back because the spring is too stiff. The tire acts like it is on the right front of a go kart going into the turn and we scrub the tire. The water can not come forward so it moves back to t he rear adding traction to the rear tires. The rears are very hooked up and start to dig making the car push. Again the car will not steer as the right front tire is being scrubbed sideways as the car heads to the outside guard rail. Sever push.
At this point the driver has to back off the throttle and moose it around the apex until he can get back on the gas pedal.
So how do you tell which scenario you have. All race shocks (dampers) have a rubber grommet that indicated the amount of shock travel. Too much travel, the spring is weak, not enuff travel the spring is too stiff. You should be close if you are copying what the other cars in you class are running spring rate wise. Again the tire pyrometer is the best tool you can use at the track.
This condition is caused by the front suspensions inability to handle the weight transferred. Under steer can be caused by improper tire inflation,
wrong camber curve, brake bias is wrong, cross weight, stagger, roll center location, but most common is improper spring rates.
Scenario 1- too soft a rt ft spring
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The right front spring is too soft and goes into coil bind. A majority of the water coming forward heads to the right front and stays there.
The water sloshing to the right comes over to the right side of the tub and since the right rear spring is too soft,
the water sloshes against the tub wall and the right rear tire really digs in because of all the added weight.
The car will not steer as the right front tire is being scrubbed sideways, the tire literally is shredded as the car heads to the outside guard rail. Sever push.
At this point the driver has to back off the throttle and moose it around the apex until he can get back on the gas pedal.
Scenario 2 – too stiff a rt ft spring
We have our imaginary race car with the Tupperware tub suspended with a coil spring mounted at each corner.
We hop in the car and go bombing into corner number one. we hit the brakes on corner entry and the water sloshes forward.
The right front spring is too stiff. We have the typical go kart situation. The water coming forward heads to the right front and is kicked back because the spring is too stiff. The tire acts like it is on the right front of a go kart going into the turn and we scrub the tire. The water can not come forward so it moves back to t he rear adding traction to the rear tires. The rears are very hooked up and start to dig making the car push. Again the car will not steer as the right front tire is being scrubbed sideways as the car heads to the outside guard rail. Sever push.
At this point the driver has to back off the throttle and moose it around the apex until he can get back on the gas pedal.
So how do you tell which scenario you have. All race shocks (dampers) have a rubber grommet that indicated the amount of shock travel. Too much travel, the spring is weak, not enuff travel the spring is too stiff. You should be close if you are copying what the other cars in you class are running spring rate wise. Again the tire pyrometer is the best tool you can use at the track.
- #678
radracr
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I'm not worthy...:rofl:….I'm not worthy but I am drinking a Modello trying to digest your Tupperware. (I ran outta popcorn…)
Taking a trip in the way-back machine, I've studied the videos from when we broke the track record and when we couldn't get out of our own way - this year. In particular, I'm studied the RF. When we broke the track record the RF was stuck to the track to the point where it looked like the rim was going to come out of the tire. When we ran this past race it was clear that the RF was 'just there for the ride'. Now, a lot has changed. We no longer have anti-dive and the RC, by default is much different. When we starting taking out the anti dive out it became clear how much more travel we were seeing. I'll have to go back and look but I believe we ran a 950# RF, 800# LF, 300#RR and 150#LR with 12/4 shocks on the front.
I believe the anti dive was/is telling us that the car needs more spring - just about like the 'book'.
It's worth a shot anyway…
But first, I have to figure out where my ridiculous oil leak is coming from. Looking at the headers it looks like it's coming out from the intake endrails.
Ranger Mike - YOU ARE THE MAN...
Taking a trip in the way-back machine, I've studied the videos from when we broke the track record and when we couldn't get out of our own way - this year. In particular, I'm studied the RF. When we broke the track record the RF was stuck to the track to the point where it looked like the rim was going to come out of the tire. When we ran this past race it was clear that the RF was 'just there for the ride'. Now, a lot has changed. We no longer have anti-dive and the RC, by default is much different. When we starting taking out the anti dive out it became clear how much more travel we were seeing. I'll have to go back and look but I believe we ran a 950# RF, 800# LF, 300#RR and 150#LR with 12/4 shocks on the front.
I believe the anti dive was/is telling us that the car needs more spring - just about like the 'book'.
It's worth a shot anyway…
But first, I have to figure out where my ridiculous oil leak is coming from. Looking at the headers it looks like it's coming out from the intake endrails.
Ranger Mike - YOU ARE THE MAN...
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thanks Rad..hope you get a checker this weekend
- #680
radracr
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Could I interpret what you saying as having too much spring split on the front - 150#?
No racing until the May 17th. This will give me lots of time to work out the details, and change the cam. Based upon our shock travel = ~1.3" each side I'm inclined to 'go by the book' for the front springs.
No racing until the May 17th. This will give me lots of time to work out the details, and change the cam. Based upon our shock travel = ~1.3" each side I'm inclined to 'go by the book' for the front springs.
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Radracer - since you have time before the next race..on post 625 page 35 you said your front motion rate was 2. Is that right?
also I could not find what size Anti roll bar ( sway bar) you have. can you tell me?
I am working on reply about spring split and hope you can get ARB data ..if you are not running one..its ok just need to know..
also I could not find what size Anti roll bar ( sway bar) you have. can you tell me?
I am working on reply about spring split and hope you can get ARB data ..if you are not running one..its ok just need to know..
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Rad - you are getting 1.5 inch shock travel but what is the wheel travel?
what is wheel travel total per one inch shock travel?
what is the shock travel at 3 inch wheel travel?
pls reply with the shock travel vs. wheel travel on all 4 corners..
this is critical
There is a difference between wheel travel and shock travel.
We shoot for 3 inch of wheel travel on right front and 2 inch wheel travel on right rear minimum.
Ideally you want 3 inch wheel travel on all 4 wheels but it is difficult to get this. You want the 3 inch wheel travel droop on the left rear and 3 inch up travel on the right front. This is optimum set up and reality and how you have mounted the shocks will determine the outcome.
We shoot for 1 1/2 to 1 3/4 inch shock travel on rt ft and 2 to 2 1/4 inch on right rear shock with ideal textbook mounting at proper angle.
How you have mounted the shock will determine the ratio of wheel travel to shock travel.
FIND THIS RATIO. Take out the rt ft spring and move the spindle it 3 inch and note shock travel over the 3 inch of wheel travel. Do the same on all 4 corners.
Example- if you get 1 inch right front wheel travel and 2 inch right rear travel the right rear is getting more bite than the right front and the car will push.
If you only get 1 inch wheel travel the car will not get good traction and he car will drift.
Too much wheel travel up front means the car is loose and too much wheel travel at the rear means we have a push condition.
So how do you tell which scenario you have. All race shocks (dampers) have a rubber grommet that indicated the amount of shock travel. Too much travel, the spring is weak, not enough travel the spring is too stiff. You should be close if you are copying what the other cars in you class are running spring rate wise. Again the tire pyrometer is the best tool you can use at the track.
Shock rebound controls 75 % of what makes the car fast. Stiffer rebound on the left side slows weight transfer to the right on corner entry so you can drive deeper into the turn.
what is wheel travel total per one inch shock travel?
what is the shock travel at 3 inch wheel travel?
pls reply with the shock travel vs. wheel travel on all 4 corners..
this is critical
There is a difference between wheel travel and shock travel.
We shoot for 3 inch of wheel travel on right front and 2 inch wheel travel on right rear minimum.
Ideally you want 3 inch wheel travel on all 4 wheels but it is difficult to get this. You want the 3 inch wheel travel droop on the left rear and 3 inch up travel on the right front. This is optimum set up and reality and how you have mounted the shocks will determine the outcome.
We shoot for 1 1/2 to 1 3/4 inch shock travel on rt ft and 2 to 2 1/4 inch on right rear shock with ideal textbook mounting at proper angle.
How you have mounted the shock will determine the ratio of wheel travel to shock travel.
FIND THIS RATIO. Take out the rt ft spring and move the spindle it 3 inch and note shock travel over the 3 inch of wheel travel. Do the same on all 4 corners.
Example- if you get 1 inch right front wheel travel and 2 inch right rear travel the right rear is getting more bite than the right front and the car will push.
If you only get 1 inch wheel travel the car will not get good traction and he car will drift.
Too much wheel travel up front means the car is loose and too much wheel travel at the rear means we have a push condition.
So how do you tell which scenario you have. All race shocks (dampers) have a rubber grommet that indicated the amount of shock travel. Too much travel, the spring is weak, not enough travel the spring is too stiff. You should be close if you are copying what the other cars in you class are running spring rate wise. Again the tire pyrometer is the best tool you can use at the track.
Shock rebound controls 75 % of what makes the car fast. Stiffer rebound on the left side slows weight transfer to the right on corner entry so you can drive deeper into the turn.
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- #683
radracr
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Ranger Mike,
All I know about my ARB is that it came off of a 1978 Trans Am and is 1-1/4" diameter.
As far as motion ratio, the software says that with a 950#RF spring the RF wheel rate is 271. @ 800# LF the wheel rate is 229. Track with on the RF = 35.6. LF = 32.0. My Right Swing Arm is 60.7 and the Left is 55.1. Right scrub radius is 7.0 Left is 5.3.
I'll keep digging…and measuring…
I'm all but committed to switch to Eibach 1050# and 1000#.
I think I'm getting too much front wheel travel. As I watch the videos I can see the RF tuck waaay up in the fender.
All I know about my ARB is that it came off of a 1978 Trans Am and is 1-1/4" diameter.
As far as motion ratio, the software says that with a 950#RF spring the RF wheel rate is 271. @ 800# LF the wheel rate is 229. Track with on the RF = 35.6. LF = 32.0. My Right Swing Arm is 60.7 and the Left is 55.1. Right scrub radius is 7.0 Left is 5.3.
I'll keep digging…and measuring…
I'm all but committed to switch to Eibach 1050# and 1000#.
I think I'm getting too much front wheel travel. As I watch the videos I can see the RF tuck waaay up in the fender.
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- #684
radracr
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I'm not comfortable in the accuracy of these number but here it goes - the fronts don't have rubbers on them and I'm not sure if I 'reset' the rear rubbers.
RF = 1.6
LF = 1.3
RR = 2.3
LR = 2.8
RF = 1.6
LF = 1.3
RR = 2.3
LR = 2.8
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radracer..the following may not be accurate as I do not have access to measurements on your particular car...motion rates of A-arm and sway bar are questionable.
Not knowing degree of banking and your tire grip means my Gs' may be off and total weight transferred is a guess. Other weasel words are the height of your Center of Gravity used.
I did find the sway bar rating..took a guess on the mounting location.
First let's clear up wheel rate vs. wheel load rate. For the purest who like digging into the minutest detail the additional calculations required for wheel load rate will yield a number VERY close to the wheel rate. Don’t worry about the piss ants take care of the eleph-ants. The illustration I attached is for the larger GMC big body cars and is longer than the A body A-Arms used on the smaller cars. These dimensions are 9.13” to spring pocket centerline and 13.25 distance to ball joint center. So the motion rate would be 9.13 / 13.25 = .686. this figure squared is .475 which is the motion rate of this A-arm.
if we have 1000# spring on the left front the wheel rate would be 1000 x .475= 475 pounds.
Looking back on previous posts we have 542# coming forward on the Tupperware race car.
You have a front motion rate of .475
rear motion rate of .53
you have a 3300 pound car
we know 542# is coming forward and
378# is transferring to the right.
the weight going to the right side is 54% to front = 204#
the RR will see 174#
Lets look at your setup when you set the track record
LF 800 RF 950
LR 150 RR 300
last years RC was 1.9H, 8.5L! The car acted like it had a 2-ton gorilla jumping
up and down on a 5-foot torque wrench! It would roll on the Right side severely.
the Front roll center was offset significantly to the left and the
RF wheel was glued to the track. The RC being offset to the
left created a huge amount of body roll download the RT front tire.
Your first race outing this year
Loose in loose out
LF 800 RF 950
LR 200 RR 175
Your Sway Bar
One thing we have not looked at is the ARB or sway bar you use.
I figure its motion rate at being mounted 2 inch from the lower ball joint would be .72 motion rate
A 1978 Trans Am sway bar 1. 25 ( 30 mm) with 223 # spring rate.
223# times .72 motion rate = 160#
we use this 160# to figure the proper spring package for the front end.
We have calculated 542# weight coming forward.
#542 – 160# = 382# if we divide by two we get 191 # for each wheel
The 950# spring on the Right Front has Motion rate of .475
.475 x 950# = 451# wheel rate which handles the 180# + 204# = 384# of weight coming to the right front wheel.
This may be a little heavy. Check wheel travel.
You may want to be brave and look at a softer left front spring. You ran 700# spring before.
RF = 1.6
LF = 1.3
RR = 2.3
LR = 2.8
Rear spring package
the weight going to the right side is 54% to front = 204#
the RR will see 174#
Looking at the RR spring we have
175# spring using .53 MR = 93# spring rate
but the RR will see 174# coming over.
this is 174# weight on the 93# RT Rear spring rate. Not good.
We know the end of the race car that has a weak spring package will snap before
the other end and I suspect this is your cause of the loose in condition.
Right Rear is collapsing at turn in.
The year you set the track record the 300# RR spring
meant you had 174# handled by a 159# RR spring rate..much better
a 325# RR spring may be about right
as reference
by the “ book “ on a 3200 pound stock car alum. head on medium bank track with spec tires
probably a little on the heavy side regarding springs
LF 1000 RF 1050
LR 250 RR 225
The best thing you can do is put grease on the front shocks to measure the travel. Maybe fabricate a dowel rod travel indicator for left side shocks. Simple drill rod hose clamped to shock and a piece of aluminum with hole drilled in it and rubber o-ring would do it.
This is my best guess on the chassis.
Not knowing degree of banking and your tire grip means my Gs' may be off and total weight transferred is a guess. Other weasel words are the height of your Center of Gravity used.
I did find the sway bar rating..took a guess on the mounting location.
First let's clear up wheel rate vs. wheel load rate. For the purest who like digging into the minutest detail the additional calculations required for wheel load rate will yield a number VERY close to the wheel rate. Don’t worry about the piss ants take care of the eleph-ants. The illustration I attached is for the larger GMC big body cars and is longer than the A body A-Arms used on the smaller cars. These dimensions are 9.13” to spring pocket centerline and 13.25 distance to ball joint center. So the motion rate would be 9.13 / 13.25 = .686. this figure squared is .475 which is the motion rate of this A-arm.
if we have 1000# spring on the left front the wheel rate would be 1000 x .475= 475 pounds.
Looking back on previous posts we have 542# coming forward on the Tupperware race car.
You have a front motion rate of .475
rear motion rate of .53
you have a 3300 pound car
we know 542# is coming forward and
378# is transferring to the right.
the weight going to the right side is 54% to front = 204#
the RR will see 174#
Lets look at your setup when you set the track record
LF 800 RF 950
LR 150 RR 300
last years RC was 1.9H, 8.5L! The car acted like it had a 2-ton gorilla jumping
up and down on a 5-foot torque wrench! It would roll on the Right side severely.
the Front roll center was offset significantly to the left and the
RF wheel was glued to the track. The RC being offset to the
left created a huge amount of body roll download the RT front tire.
Your first race outing this year
Loose in loose out
LF 800 RF 950
LR 200 RR 175
Your Sway Bar
One thing we have not looked at is the ARB or sway bar you use.
I figure its motion rate at being mounted 2 inch from the lower ball joint would be .72 motion rate
A 1978 Trans Am sway bar 1. 25 ( 30 mm) with 223 # spring rate.
223# times .72 motion rate = 160#
we use this 160# to figure the proper spring package for the front end.
We have calculated 542# weight coming forward.
#542 – 160# = 382# if we divide by two we get 191 # for each wheel
The 950# spring on the Right Front has Motion rate of .475
.475 x 950# = 451# wheel rate which handles the 180# + 204# = 384# of weight coming to the right front wheel.
This may be a little heavy. Check wheel travel.
You may want to be brave and look at a softer left front spring. You ran 700# spring before.
RF = 1.6
LF = 1.3
RR = 2.3
LR = 2.8
Rear spring package
the weight going to the right side is 54% to front = 204#
the RR will see 174#
Looking at the RR spring we have
175# spring using .53 MR = 93# spring rate
but the RR will see 174# coming over.
this is 174# weight on the 93# RT Rear spring rate. Not good.
We know the end of the race car that has a weak spring package will snap before
the other end and I suspect this is your cause of the loose in condition.
Right Rear is collapsing at turn in.
The year you set the track record the 300# RR spring
meant you had 174# handled by a 159# RR spring rate..much better
a 325# RR spring may be about right
as reference
by the “ book “ on a 3200 pound stock car alum. head on medium bank track with spec tires
probably a little on the heavy side regarding springs
LF 1000 RF 1050
LR 250 RR 225
The best thing you can do is put grease on the front shocks to measure the travel. Maybe fabricate a dowel rod travel indicator for left side shocks. Simple drill rod hose clamped to shock and a piece of aluminum with hole drilled in it and rubber o-ring would do it.
This is my best guess on the chassis.
Attachments
- #686
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I have pondered the obvious question - When I scale my race car, ( use electronic scales under each wheel) I get wheel loads on the rear scales of 975 # on the Left Rear wheel scale, and 485# on Right Rear wheel scale. But only have 200 # springs in the left and right rear of the car? This appears to be a disconnect.
What is going on?
The answer is actually in two parts and I now throw it open for discussion.
What is going on?
The answer is actually in two parts and I now throw it open for discussion.
- #687
radracr
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I'll be curious to hear this answer. First thought is compression of the springs but that would mean the LR would be in near coil bind.
Some old notes say:
Motion ratio: RF = .607; LF = .671
My upper and lower control arms from a 70-81 Camaro.
I think it's time to run some more computer numbers.
You've go me confused over the LF spring rate. Your last supposition has me running a stiffer RR and softer yet LF. But how will this allow the weight to transfer through the RC to the RF?
My rear springs are 17" to centerline. Tire to centerline RR = 34.1; LR = 32.1
Front ARB motion ratio = 1.007
Some old notes say:
Motion ratio: RF = .607; LF = .671
My upper and lower control arms from a 70-81 Camaro.
I think it's time to run some more computer numbers.
You've go me confused over the LF spring rate. Your last supposition has me running a stiffer RR and softer yet LF. But how will this allow the weight to transfer through the RC to the RF?
My rear springs are 17" to centerline. Tire to centerline RR = 34.1; LR = 32.1
Front ARB motion ratio = 1.007
- #688
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radarcer – you have the most popular front end set up going. The GM Metric control arm is most used in hobby racing today. The ARB (sway bar) motion rate is almost 1:1 which means the 223# will subtract the load rate required by each front wheel spring. I came up with a motion rate of .54 for the lower control arm and if you did the math regarding instant centers etc.. the wheel load rate would be close to your .6 figure. That said it still looks to me like you have a soft RR spring and front end may be a little stiffer than ideal. All this math is of no consequence and I recommend you do the following.
3 inch wheel travel- so why get hung up on 3 inch wheel travel? For a typical door slammer class racing, on a fairly flat to medium bank oval paved track, this 3 inch travel on the right front wheel will yield the best handling possible. Excess travel means you have weak springs the camber build and bump steer go away and less than 3 inch travel means too stiff a spring and is less than the best you can get with this set up. If you have 2.5 inch travel that is great but still could be maximized as you are wasting 1/2 inch travel which could be used to give that much better grip than the other racer. Races are won by 1/10ths and some times by 1/100s of a second as we all know. You want your spring package to take the weight transferred and compress the 3 inch during corner entry. Then push the weight back just as you have completed mid corner transition and throw the weight to the rear tires for good traction at corner exit. The springs do this the shocks ( dampers) control the timing of this.
In an ideal world on a perfect track we want 3 inch droop on the left side front and rear and 3 inch compression on the right side front and rear. This is probably not going to happen. I would settle for 2 inch on the rear if you can not run a panhard bar due to the track rules.
The way we measure this is to find the shock travel length when the wheel is at the ideal 3 inch point. Unless you want to hang cameras near each wheel this is the cheapest best way of measuring things. Take the time to fabricate the droop indicators for the left side as the shock travel indicators are good for compression only. Cut rubber grommets and install them on the right side shocks if they are not there. This is the simplest and cheapest way to tell you why you are pushing or loose. Make sure your driver does not drive over sever drop off when exiting the track. Once you get the correct Roll Centers and they stay more or less constant thru 3 inch of wheel travel , and your camber build and bump steer are ok over the 3 inches, once you have proper ballast for the track rules % rear and % left side weight, once you dial in known good cross weight and have correct stagger get off the computer.
The computer is a good Tool but sometimes it will mess with your mind. Head for the track and start using the stop watch and pyrometer and look at the shock travel indicators. Happiness is a hot lap with 2 inch showing on the travel indicators because you are getting close. So the next time you pulling into the pits you can allow your self the pleasure of secretly smiling because you know you have the roll centers right, car is scaled correct and camber , caster and bump is correct and you are only 3 steps away from the checker.
There are only a finite number of things that can keep you out of the winners circle. Stagger is wrong, brake bias wrong, rear roll center wrong but you have no control over this, front roll center is wrong (should not be since you know it and its movement) , tire pressure..( if this keeps out from winning – QUIT) cross weight wrong..see tire pressure comment, bump steer, camber cater rear steer wrong- see tire pressure comment. What is left is spring rates and you knowhow to check these now, at the track, for immediate feed back.
That poor yahoo next to you in the pits will wonder why he pushes going in but is loose off and you can watch him chase his tail trying to band-aid the car all night. Ha..you been there, done that. Step 1 is to get the 3 inch travel dialed in then step 2 is fine tune the rate of transfer forward and returning it back. Step 3 is finding the entrance to Victory Lane. I would give you three races until you start to dominate, RADRACER.
3 inch wheel travel- so why get hung up on 3 inch wheel travel? For a typical door slammer class racing, on a fairly flat to medium bank oval paved track, this 3 inch travel on the right front wheel will yield the best handling possible. Excess travel means you have weak springs the camber build and bump steer go away and less than 3 inch travel means too stiff a spring and is less than the best you can get with this set up. If you have 2.5 inch travel that is great but still could be maximized as you are wasting 1/2 inch travel which could be used to give that much better grip than the other racer. Races are won by 1/10ths and some times by 1/100s of a second as we all know. You want your spring package to take the weight transferred and compress the 3 inch during corner entry. Then push the weight back just as you have completed mid corner transition and throw the weight to the rear tires for good traction at corner exit. The springs do this the shocks ( dampers) control the timing of this.
In an ideal world on a perfect track we want 3 inch droop on the left side front and rear and 3 inch compression on the right side front and rear. This is probably not going to happen. I would settle for 2 inch on the rear if you can not run a panhard bar due to the track rules.
The way we measure this is to find the shock travel length when the wheel is at the ideal 3 inch point. Unless you want to hang cameras near each wheel this is the cheapest best way of measuring things. Take the time to fabricate the droop indicators for the left side as the shock travel indicators are good for compression only. Cut rubber grommets and install them on the right side shocks if they are not there. This is the simplest and cheapest way to tell you why you are pushing or loose. Make sure your driver does not drive over sever drop off when exiting the track. Once you get the correct Roll Centers and they stay more or less constant thru 3 inch of wheel travel , and your camber build and bump steer are ok over the 3 inches, once you have proper ballast for the track rules % rear and % left side weight, once you dial in known good cross weight and have correct stagger get off the computer.
The computer is a good Tool but sometimes it will mess with your mind. Head for the track and start using the stop watch and pyrometer and look at the shock travel indicators. Happiness is a hot lap with 2 inch showing on the travel indicators because you are getting close. So the next time you pulling into the pits you can allow your self the pleasure of secretly smiling because you know you have the roll centers right, car is scaled correct and camber , caster and bump is correct and you are only 3 steps away from the checker.
There are only a finite number of things that can keep you out of the winners circle. Stagger is wrong, brake bias wrong, rear roll center wrong but you have no control over this, front roll center is wrong (should not be since you know it and its movement) , tire pressure..( if this keeps out from winning – QUIT) cross weight wrong..see tire pressure comment, bump steer, camber cater rear steer wrong- see tire pressure comment. What is left is spring rates and you knowhow to check these now, at the track, for immediate feed back.
That poor yahoo next to you in the pits will wonder why he pushes going in but is loose off and you can watch him chase his tail trying to band-aid the car all night. Ha..you been there, done that. Step 1 is to get the 3 inch travel dialed in then step 2 is fine tune the rate of transfer forward and returning it back. Step 3 is finding the entrance to Victory Lane. I would give you three races until you start to dominate, RADRACER.
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- #689
radracr
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Ok, I've had a few beers, a few steaks, even a few winks no I'm on a mission to, as we say in Texas - git'r done. Again, one of my guiding lights has been to study - frame by frame - when the car was bad-fast. It closely replicated what you are saying. The Right side compressed - the RF more so than the RR, and at the left side rose - or drooped as you say. At the apex the car seems to settle as it looks square and then it's square off.
But the things that are tripping me up are KNOWING that the car had the a-arms mounted in stock location and therefore a LOT of anti dive. What it also had were tires that were ALL 5# more than what I have been running. Range Mike, correct me if I'm wrong but wouldn't this all equate to the car thinking it had stiffer springs?
The recent race has the car looking pretty square - level corner entry through the apex. It's clear that the RR is not hooked up at all through the turns!...
But the things that are tripping me up are KNOWING that the car had the a-arms mounted in stock location and therefore a LOT of anti dive. What it also had were tires that were ALL 5# more than what I have been running. Range Mike, correct me if I'm wrong but wouldn't this all equate to the car thinking it had stiffer springs?
The recent race has the car looking pretty square - level corner entry through the apex. It's clear that the RR is not hooked up at all through the turns!...
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I have pondered the obvious question- When I scale my race car, I get wheel loads on the rear scales of 975 # on the Left Rear wheel scale
and 485# on Right Rear wheel scale. But only have 200 # springs in the rear of the car? This appears to be a disconnect. What is going on?
The answer is actually in two parts and I now throw it open for discussion.
Ok no one took the bait.
There is a difference between support and suspend. Support is what you give your ex-wife for years ( actually it is where the load acts directly one an area ) .If we place a wheel on top of the scale we have mass being pulled by gravity making the scale reading. When we have a suspension of the load things are a little more complicated. Image the play ground teeter totter.
When two kids of equal weight sit at the same distance from the pivot point there is balance. You could stick a 1/1 diameter wood dowel rid under each side and the teeter totter would not move. Gravity is still in place but the equal weight at equal distance from the pivot point cancels out the effect of gravity even though the weight of each child could easy break the little 1/4” wood stick.
When we scale the race car we have both. On the rear of the car we have about 400 lbs. unsprung weight of tires wheels, brake rotors calipers etc...and we have the sprung weight of the rest of the car ( 1118#).
We know 378# is being transferred to the right and since the car is 46% rear weight this is 378 x .46= 174 # to deal with. We know the rear motion rate is .53 so we have 174# x .53= 92 pounds to deal with. This is dynamic weight transfer. We need to get the car to remain suspended at rest and provide some type of stability through the turn so a 92# spring would not do this. The rear spring needs to be twice this rate so we typically see a 175# or 200# rear spring. The faster we can go into a turn, the higher the banking, the more grip our tires have the higher the center of gravity all add up to stiffer springs.
and 485# on Right Rear wheel scale. But only have 200 # springs in the rear of the car? This appears to be a disconnect. What is going on?
The answer is actually in two parts and I now throw it open for discussion.
Ok no one took the bait.
There is a difference between support and suspend. Support is what you give your ex-wife for years ( actually it is where the load acts directly one an area ) .If we place a wheel on top of the scale we have mass being pulled by gravity making the scale reading. When we have a suspension of the load things are a little more complicated. Image the play ground teeter totter.
When two kids of equal weight sit at the same distance from the pivot point there is balance. You could stick a 1/1 diameter wood dowel rid under each side and the teeter totter would not move. Gravity is still in place but the equal weight at equal distance from the pivot point cancels out the effect of gravity even though the weight of each child could easy break the little 1/4” wood stick.
When we scale the race car we have both. On the rear of the car we have about 400 lbs. unsprung weight of tires wheels, brake rotors calipers etc...and we have the sprung weight of the rest of the car ( 1118#).
We know 378# is being transferred to the right and since the car is 46% rear weight this is 378 x .46= 174 # to deal with. We know the rear motion rate is .53 so we have 174# x .53= 92 pounds to deal with. This is dynamic weight transfer. We need to get the car to remain suspended at rest and provide some type of stability through the turn so a 92# spring would not do this. The rear spring needs to be twice this rate so we typically see a 175# or 200# rear spring. The faster we can go into a turn, the higher the banking, the more grip our tires have the higher the center of gravity all add up to stiffer springs.
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When you sweep out the garage with that shop broom you get the best job done when the broom handle is at 45 ° angle to the floor. If you were to hold the handle at 90° and push it you would not get much done. If you were to lower the handle to 12° to the floor and push it the broom would scoot over the rubbish and you would not get a clean sweep.
Looking at the attached pics on Page 27 Post # 479. ( I am not good at white out, boys) . The stock set up with roll center at car centerline and at 3 inch height has a pretty good set up for left and right hand turns. The tire contact reaction force is at 15° to the RC. The cars CG is at 90° to the RC. When you enter the turn, the tires grip, create the reaction force, the body rotates , the ARB or sway bar counter this and and weight compresses the front springs. This is pretty good and the best you are going to get when you must turn right AND left.
If we offset the RC to the right side by 3 inches of car centerline and at 3 inch height as with a stock car late model set up the tire contact reaction force is now at 22° to the RC. The cars CG is almost straight line to reaction force vector ( 20° offset ). Now when the CG wants to rotate about the RC and since we only want car about turning left we have the maximum weight loading the right front tire ( if we have the shock spring package correct). If we have the Roll Center offset too far to the right we get closer tot the magic 45° angle and start to lift the left front tire like the old sprint cars did.
If we offset the RC to the left side by 3 inches of car centerline and at 3 inch height we have trouble. The tire contact reaction force is now at 12° to the RC. The CG is 133° to the tire contact reaction force vector and bass ackwards. Not much rotation force wil be resisted by the tire reaction force with this set up. When you enter the turn, the tires grip, but the reaction force is very weak. We have not created the reaction force necessary to resist Centrifugal force. The body rotates and weight compresses the right front spring but not enough to provide the necessary down force. Since we have no front grip we push going in (under steer condition at turn entry). The right front tire will be pushed sideways. Since we did not compress the springs enough, and the sway bar did all the work since we only had severe body roll and very little spring compression , under acceleration there is not be enough weight transfer from left front to right rear to hook up the car. Loose coming out ( over steer on turn exit).
a note to Radracer- when you make major chassis changes like re-mounting control arms and relocating Roll Centers it is vary hard to compare old set up notes to current set up because you have changes the chassis geometry in a huge way.
Looking at the attached pics on Page 27 Post # 479. ( I am not good at white out, boys) . The stock set up with roll center at car centerline and at 3 inch height has a pretty good set up for left and right hand turns. The tire contact reaction force is at 15° to the RC. The cars CG is at 90° to the RC. When you enter the turn, the tires grip, create the reaction force, the body rotates , the ARB or sway bar counter this and and weight compresses the front springs. This is pretty good and the best you are going to get when you must turn right AND left.
If we offset the RC to the right side by 3 inches of car centerline and at 3 inch height as with a stock car late model set up the tire contact reaction force is now at 22° to the RC. The cars CG is almost straight line to reaction force vector ( 20° offset ). Now when the CG wants to rotate about the RC and since we only want car about turning left we have the maximum weight loading the right front tire ( if we have the shock spring package correct). If we have the Roll Center offset too far to the right we get closer tot the magic 45° angle and start to lift the left front tire like the old sprint cars did.
If we offset the RC to the left side by 3 inches of car centerline and at 3 inch height we have trouble. The tire contact reaction force is now at 12° to the RC. The CG is 133° to the tire contact reaction force vector and bass ackwards. Not much rotation force wil be resisted by the tire reaction force with this set up. When you enter the turn, the tires grip, but the reaction force is very weak. We have not created the reaction force necessary to resist Centrifugal force. The body rotates and weight compresses the right front spring but not enough to provide the necessary down force. Since we have no front grip we push going in (under steer condition at turn entry). The right front tire will be pushed sideways. Since we did not compress the springs enough, and the sway bar did all the work since we only had severe body roll and very little spring compression , under acceleration there is not be enough weight transfer from left front to right rear to hook up the car. Loose coming out ( over steer on turn exit).
a note to Radracer- when you make major chassis changes like re-mounting control arms and relocating Roll Centers it is vary hard to compare old set up notes to current set up because you have changes the chassis geometry in a huge way.
Attachments
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- #692
radracr
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Update:
1050 RF, 1000 LF, 250 RR, 200 LR = Text book. The car was terrible - loose all the way through. The RF is sticking better but not great. Tire temps improved.
Changed to 1050RF, 1000LF, 200RR, 175LR. We also changed the front ride height so that it was 7" across. It was 6. MUCH BETTER. The RF is digging hard. The car was also more stable through the turn. The effect here was improving the front RC. And it did.
Shock indicators = 1.0"RF, 1.4"LF, 2.0"RR, 2.4"LR
The car is getting better. Based upon the shock indicators we have some work to do on the front. With the motion ratios of .6 and .67, the RF and LF are traveling 1.67" and 1.94" respectively. Simply not enough.
Rear motion ratios .66RR and .70LR, the tires are traveling 3.0" and 3.33" respectively. Close.
If I'm going by travel, then the LR needs a stiffer spring (200#?)and the RF needs a softer spring (950#?) and maybe a 900# on the LF?. I would also suspect that we would need to start with a much higher front ride height (7.5"?) so that the RC stays where we want.One note: the right side tires have very little rubber left. We put the bald tire on the RF to get the stagger we needed across the rear. The car simply pushed up the track but remarkably appeared to want to turn better. When we put the bald tire on the back - reducing rear stagger - the tire was wicked loose and didn't turn as well. The car was also faster when it was tight.
We did not check droop. Based upon video that I saw the droop is near what we want.
Lot's learned.
1050 RF, 1000 LF, 250 RR, 200 LR = Text book. The car was terrible - loose all the way through. The RF is sticking better but not great. Tire temps improved.
Changed to 1050RF, 1000LF, 200RR, 175LR. We also changed the front ride height so that it was 7" across. It was 6. MUCH BETTER. The RF is digging hard. The car was also more stable through the turn. The effect here was improving the front RC. And it did.
Shock indicators = 1.0"RF, 1.4"LF, 2.0"RR, 2.4"LR
The car is getting better. Based upon the shock indicators we have some work to do on the front. With the motion ratios of .6 and .67, the RF and LF are traveling 1.67" and 1.94" respectively. Simply not enough.
Rear motion ratios .66RR and .70LR, the tires are traveling 3.0" and 3.33" respectively. Close.
If I'm going by travel, then the LR needs a stiffer spring (200#?)and the RF needs a softer spring (950#?) and maybe a 900# on the LF?. I would also suspect that we would need to start with a much higher front ride height (7.5"?) so that the RC stays where we want.One note: the right side tires have very little rubber left. We put the bald tire on the RF to get the stagger we needed across the rear. The car simply pushed up the track but remarkably appeared to want to turn better. When we put the bald tire on the back - reducing rear stagger - the tire was wicked loose and didn't turn as well. The car was also faster when it was tight.
We did not check droop. Based upon video that I saw the droop is near what we want.
Lot's learned.
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Lots learned...this is the whole point of this forum. Rad- now you know what the car is doing ( not doing) and more importantly, you know why! And you are getting real close to the winning set up. The old bald tire was getting more down load and the car was trying to pivot on it in the turn but still not enough download because the springs are not soft enough to dump the required load. I agree the fronts may be a tad stiff..I would not mess with the rear springs as softening the front is same as stiffening the rears. Your rear shock travels are very close. You are two weekend away from the checker and there is not much more i can do front the bench. Keep good notes and change one thing at a time though in this case the front springs may both get swapped out since it looks like they are stiff.
- #694
radracr
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Ranger Mike - thanks for continuing to follow me along. I truly appreciate the feedback and insight. You have forced me and my team to continue to hunt for information. AND, measure…measure…measure...
Now, I know you say that I can't compare this year to last year BUT…I've studied the videos from this past weekend… guess what? That RF…in the second race where it had a 'good' tire looks A LOT like when we broke the track record! The rim is pushing out of the tire! My point is that, while the set ups are vastly different the net output is remarkably similar! I'll be putting 900s across the front. But before I do that I'll be verifying the shock travel and converting to wheel travel. Goal = 3.0" at all four corners.
Who knows I may opt to put a pair of 175s in the rear. They give us three practice sessions so a rear spring change is pretty easy.
Also, as if all the changes weren't enough we switched out the 'heavy compression' shocks and put the 12/4 shocks back in. The jury isn't out quite yet on this.
I'd be curious to see some posts by you on shocks…err, dampers…
Cheers!
Now, I know you say that I can't compare this year to last year BUT…I've studied the videos from this past weekend… guess what? That RF…in the second race where it had a 'good' tire looks A LOT like when we broke the track record! The rim is pushing out of the tire! My point is that, while the set ups are vastly different the net output is remarkably similar! I'll be putting 900s across the front. But before I do that I'll be verifying the shock travel and converting to wheel travel. Goal = 3.0" at all four corners.
Who knows I may opt to put a pair of 175s in the rear. They give us three practice sessions so a rear spring change is pretty easy.
Also, as if all the changes weren't enough we switched out the 'heavy compression' shocks and put the 12/4 shocks back in. The jury isn't out quite yet on this.
I'd be curious to see some posts by you on shocks…err, dampers…
Cheers!
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- #695
rick7343
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"I'd be curious to see some posts by you on shocks…err, dampers…
Cheers! "
And tire pressures!
Cheers! "
And tire pressures!
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been real busy this month.. since 2 hours from INDY...i will get on the shock ' damper ' reply when i return..mean time please post your two biggest questions on this subject so i can cover all the bases..
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I contacted Jim Stimola about dampers / shocks. He does our formula car shocks.
Please post your questions about shocks ( dampers) and I will ask Jim as he has decades of experience in this field.
the only stupid question is the one you DONT ask.
James Stimola
SRP Engineering
www.srpengineering.com
Please post your questions about shocks ( dampers) and I will ask Jim as he has decades of experience in this field.
the only stupid question is the one you DONT ask.
James Stimola
SRP Engineering
www.srpengineering.com
- #698
radracr
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I know shocks by numbers: 4, 6, 8, 9, etc. but I'm sure these correlate into velocites? And, which is a better way to undestand a shock - number or velocity?
Next, how to establish a shock baseline for each corner? Do both front shocks need to be equal? Both rears equal? Or is assymetry better?
Next, I was reading where shocks are selected based upon a driving style? True? And how to determine? I tend to be the type that drives in DEEP, applies brake pressure and wheel and then let's off and rolls into the throttle fairly quickly.) I have since learned that not so much brake, dragging the brake and picking up the throttle is better.)
Do compression and rebound correlate? In other words, you have to match a specific rebound and compression because of the freqency of motion?
As I understand it, a shock with very low compression, say '4', allows the weight to hit the spring faster. But is this ideal? Or do you want the weight to be gradual as in a 6, 7, 8, etc?
Lastly, do a shock and spring need to be matched for a particular corner?
Next, how to establish a shock baseline for each corner? Do both front shocks need to be equal? Both rears equal? Or is assymetry better?
Next, I was reading where shocks are selected based upon a driving style? True? And how to determine? I tend to be the type that drives in DEEP, applies brake pressure and wheel and then let's off and rolls into the throttle fairly quickly.) I have since learned that not so much brake, dragging the brake and picking up the throttle is better.)
Do compression and rebound correlate? In other words, you have to match a specific rebound and compression because of the freqency of motion?
As I understand it, a shock with very low compression, say '4', allows the weight to hit the spring faster. But is this ideal? Or do you want the weight to be gradual as in a 6, 7, 8, etc?
Lastly, do a shock and spring need to be matched for a particular corner?
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i have a conference call tomorrow with Jim Stimola about the shock questions so will post after the call..last chance to ask about shocks dampers...
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rick7343
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Views on the latest suspension trends for popular classes would be a great topic.
Around here it seems the winning builders are going softer springs but stiffer shocks in our non bump stop classes.
Around here it seems the winning builders are going softer springs but stiffer shocks in our non bump stop classes.
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