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opps
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Automotive Race car suspension Class
- Thread starter Ranger Mike
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- Car Class Race Suspension
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The discussion emphasizes the importance of understanding race car suspension dynamics to improve handling and performance. Key issues include the car's tendency to push while entering corners and being loose upon exit, which can be addressed by adjusting downforce and the third link location. The roll center and instant center are critical factors in suspension design, affecting tire loading and grip during cornering. The conversation also highlights the significance of software tools like Suspension Analyzer for optimizing suspension geometry. Overall, proper suspension setup is essential for maximizing tire contact and achieving competitive performance on the track.
- #1,562
Steve2
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Ranger Mike - On page 58, you discuss brake floaters as it is used in oval track racing. What's your opinion on using brake floaters in road racing to improve rear braking? I don't recall ever seeing it used there. Would it be worth the effort or have adverse effects on corner entry?
- #1,563
LogicIndustries
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Ranger Mike said:
Not that it was a good idea, but we ran a methanol modified with a 32 gal tank back in the late 90's all over short tracks in MO, and basically every car ran the same setup. Big rectangular poly tank, NO foam, specifically to promote slosh and help turn the car in on entry.
Did it work? Yeah, I think so. Was it smart? Probably not, but I lived through it. In fact, I never saw a fuel fire once in those cars (not just my car, I mean I never saw one of them burn anywhere). That don't mean it's not possible, just means I never saw it happen.
Anyway, he's not super far off base with the size and shape of fuel cells used back in the day. I don't know of the big cells are as common now as they were back then, but I will note that every mfg still makes that same poly bladder cell that I used to run, and a pretty neat wedge shaped one too, both 32 gallons, both without foam.
Not saying you're wrong about anything, just saying that folks did used to run cells that big without foam on short tracks, and probably still do.
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Steve
I absolutely do thing brake floaters are the hot set up on left and right turn tracks. Especially if in a stock class with very rigid rules. The improved grip, heat dissipation and life extending properties are a great advantage. I also thing you have to get the computer software to find the true roll center and its path under compression and rebound. (Where have we heard this one before). Running totally stock is exactly that but there should be enough room to slide the brake floater thing thru on safety. You have latitude to change ball joints so get the adjustable height type to take care of roll center. You want no offset and no migration when in compression and rebound so try to get it as close to zero as possible. I also thing hydraulic spring centering perches or coil spring torsion thrust bearings are excellent way to add more grip and lower the lap time. Let the tech boys try to find these! Check and fix any bump steer. Big fix if you got mucho bump steer. All of these will add grip and reduce lap timers when you are out cone killing at the local autocross event.
https://www.pegasusautoracing.com/productselection.asp?Product=1870
https://www.jegs.com/i/JEGS+Performance+Products/555/81804/10002/-1?gclid=CjwKCAjw49qKBhAoEiwAHQVTo2PN-AQb8-nmOfu0pFw7Bs8r88Iz3V5zPTV7bP6yp-y2qIBHwdNsJRoC20MQAvD_BwE
https://eibach.com/us/c-119-motorsp...ing-accessories-torsion-release-bearings.html
bump steer video
Logic – Great point on safety - we all did dumb stuff like using beer barrel gas tanks but thank the Racing Gods for that one rule mandating Fuel tank foam cells. I hate rules but can sure “ live” with that one.
I absolutely do thing brake floaters are the hot set up on left and right turn tracks. Especially if in a stock class with very rigid rules. The improved grip, heat dissipation and life extending properties are a great advantage. I also thing you have to get the computer software to find the true roll center and its path under compression and rebound. (Where have we heard this one before). Running totally stock is exactly that but there should be enough room to slide the brake floater thing thru on safety. You have latitude to change ball joints so get the adjustable height type to take care of roll center. You want no offset and no migration when in compression and rebound so try to get it as close to zero as possible. I also thing hydraulic spring centering perches or coil spring torsion thrust bearings are excellent way to add more grip and lower the lap time. Let the tech boys try to find these! Check and fix any bump steer. Big fix if you got mucho bump steer. All of these will add grip and reduce lap timers when you are out cone killing at the local autocross event.
https://www.pegasusautoracing.com/productselection.asp?Product=1870
https://www.jegs.com/i/JEGS+Performance+Products/555/81804/10002/-1?gclid=CjwKCAjw49qKBhAoEiwAHQVTo2PN-AQb8-nmOfu0pFw7Bs8r88Iz3V5zPTV7bP6yp-y2qIBHwdNsJRoC20MQAvD_BwE
https://eibach.com/us/c-119-motorsp...ing-accessories-torsion-release-bearings.html
bump steer video
Logic – Great point on safety - we all did dumb stuff like using beer barrel gas tanks but thank the Racing Gods for that one rule mandating Fuel tank foam cells. I hate rules but can sure “ live” with that one.
- #1,565
Steve2
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Thanks Mike - I agree with all your suggestions, but I apparently didn't write my question clearly. I was talking about floating calipers on the axle housing and having a radius rod to the chassis. I know it's used in dirt track and some other oval racing, but how about road racing - such as SCCA GT classes?
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Why not use brake floaters on road race cars? Same reason majority of asphalt racers do not use 4 link setups on their cars.
In road racing we spend all efforts in keeping things symmetric. That’s why the roll center is “ centered “ and rolls as close to centerline as possible. Left to right side weight is equal. This is to best handle the various track turn radius and angles encountered. I have seen drivers bias one side more than the other if the track had 6 right turns and 7 left turns. To me, if you get in a wreck, is it worth taking the extra time to replace the longer radius rods or links instead of replacing the identical length piece? I think the “ keep everything neutral” tune is the way to go. You can have too many options to pick from some times and if time is critical, less options are better. Its got a push, where is it coming from??
Brake floaters as discussed on page 58 are great for a 4 link dirt setup. These racers want huge body roll in one direction and massive induced roll steer. In this case , adding one or two control rods to link the brake calipers makes sense.
Yes road racing cars can use it too but it is added expense and maintenance to keep the bird cages free and floating. Is it really worth the headache?
Deal with the Elephant first, not the piss ant. my opinion. I like your idea though. Can be an edge!
In road racing we spend all efforts in keeping things symmetric. That’s why the roll center is “ centered “ and rolls as close to centerline as possible. Left to right side weight is equal. This is to best handle the various track turn radius and angles encountered. I have seen drivers bias one side more than the other if the track had 6 right turns and 7 left turns. To me, if you get in a wreck, is it worth taking the extra time to replace the longer radius rods or links instead of replacing the identical length piece? I think the “ keep everything neutral” tune is the way to go. You can have too many options to pick from some times and if time is critical, less options are better. Its got a push, where is it coming from??
Brake floaters as discussed on page 58 are great for a 4 link dirt setup. These racers want huge body roll in one direction and massive induced roll steer. In this case , adding one or two control rods to link the brake calipers makes sense.
Yes road racing cars can use it too but it is added expense and maintenance to keep the bird cages free and floating. Is it really worth the headache?
Deal with the Elephant first, not the piss ant. my opinion. I like your idea though. Can be an edge!
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Why use coil spring thrust bearings if the shock travel is only 1 to 2 inches? If you have hard Spec tires, this is exactly where you have very small shock (wheel) movements and this is when grip is generated or lost. The racer that can maintain minimum tire download CHANGE wins. The thrust bearings allow the spring to axially twist (all coil springs twist as they compress) as it compresses without causing ANY Changes - chassis bind, increase spring rate, etc. As a spring is compressed, the helix angle decreases. This causes the spring ends to try to rotate around the spring axis. If we have the old school non flat spring end jammed into the old Chevy A-Arm pocket we have huge twist force and SPRING BEND. This throws big changes in the overall spring rate. By going to the flat end coil spring, we reduce this twist force and degree of bend but now have friction of the flat spring end twisting against the metal spring cup. Heat and friction follow and the heat adds up on a 20 lap race. Since neither end is allowed to rotate freely , then one end or the other will have to slip on the perch face. This extra rotation of the spring end coil slippage across the perch face takes energy, and takes it in an unpredictable manner. It is true that on the surface the amount of energy may seem small and insignificant, but it can actually make a discernable difference. We add bearing at both ends of the flat spring and we eliminate spring bend and reduce to very small the friction we had. Racing tip – soak these in chain saw bar oil for an hour then assemble. Do not use grease. Keep squeeze bottle of chain saw bar oil to squirt once a month.
I quote from Hyperco - Optimum race car suspension components must be designed for consistent performance, an infinite fatigue life and absolute minimum weight. At Hyperco, we look at every aspect of design. Is it as light as possible? Is it the optimal design that can be produced? We continue to research and develop materials and techniques to further our product line in the areas of performance and weight savings. Through our research and development efforts, we've designed a collection of new and innovative components. They are designed, tested and manufactured with the same attention to detail that has made our other products winners on the race track ensuring that these components also provide a Performance Advantage. In racing, tire grip and low wear rate, are critical for maximum performance. Unfortunately, one of the common characteristics of coil springs is that they do not naturally distribute their load evenly around the face of their end coils thus generating a lateral load. The lateral force creates a bending load in the shock absorber, significantly increasing its friction; the result is lower tire grip and increased wear. The Hyperco/ICP Hydraulic Load Centering Spring Perches substantially improve performance by allowing the spring forces to remain centered on the damper and eliminate lateral loads. By precise shaping of the sealing wall of both the perch and cylinder body, the perch can freely tilt as needed to evenly distribute the load over the face of the perch. The result, a reduction of bending load on the shock absorber of up to 96% along with an enhancement in mechanical grip at the tire.
We used these on the Formula car as well as the thrust bearings. On a road course – lap time was 0.200 second per lap from previous race weekend (coil over Penske shocks, same tires) . I would guess on round track , using only the thrust bearings , worth shaving at least 0.100 second lap time.
I quote from Hyperco - Optimum race car suspension components must be designed for consistent performance, an infinite fatigue life and absolute minimum weight. At Hyperco, we look at every aspect of design. Is it as light as possible? Is it the optimal design that can be produced? We continue to research and develop materials and techniques to further our product line in the areas of performance and weight savings. Through our research and development efforts, we've designed a collection of new and innovative components. They are designed, tested and manufactured with the same attention to detail that has made our other products winners on the race track ensuring that these components also provide a Performance Advantage. In racing, tire grip and low wear rate, are critical for maximum performance. Unfortunately, one of the common characteristics of coil springs is that they do not naturally distribute their load evenly around the face of their end coils thus generating a lateral load. The lateral force creates a bending load in the shock absorber, significantly increasing its friction; the result is lower tire grip and increased wear. The Hyperco/ICP Hydraulic Load Centering Spring Perches substantially improve performance by allowing the spring forces to remain centered on the damper and eliminate lateral loads. By precise shaping of the sealing wall of both the perch and cylinder body, the perch can freely tilt as needed to evenly distribute the load over the face of the perch. The result, a reduction of bending load on the shock absorber of up to 96% along with an enhancement in mechanical grip at the tire.
We used these on the Formula car as well as the thrust bearings. On a road course – lap time was 0.200 second per lap from previous race weekend (coil over Penske shocks, same tires) . I would guess on round track , using only the thrust bearings , worth shaving at least 0.100 second lap time.
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Anti Squat - revisited
Personally , I am not into ANTI anything on a race car. Adding in Anti Dive, anti squat, droop limiters etc.. to a poor performing race car to keep it from pushing is at best a Band-Aid if you think about it ...you are trying to treat the problem not the cause. I am a big believer in using a cars suspension to deal with weight transfer. I don't even like roll steer but in some classes, its all you can do to make the most with a bad situation. We all know why unsprung weight is so evil. You cannot control it. So, with that line of thought, sprung weight is " good" because we can control it..right? So how best to control the weight transfer? Springs and shocks and ARB (sway bar). Remember, Too much anti squat means BRAKE HOP
Above is 10 year old statement and you can teach an old dog new tricks..I believe in roll rear steer big time now. And if your rules dictate hard spec tires, look at anti squat. Not so much on sticky tire classes.
Draw a horizontal line thru the COG parallel with the ground
On front end, draw a vertical line from the ground thru the front axle center up to horizontal COG line. Now at this point, draw a line to the rear tire contact patch.
This is the 100% anti squat line. You want your rear IC at this line or a little over it.https://www.google.com/search?clien...placement#kpvalbx=_u5OfYbeLN4aYptQPjYewuAU121
If the IC is on the line connecting the rear tire patch with a line between the CG and the front axle centerline you have 100% anti squat. If the line falls below this point you have less than 100% anti squat. Study the illustration.
Study the attached. Less anti squat means the forces are pushing toward the front of the car by pulling at the CG at a 40° angle. The plus anti squat vector pushes to lift the front end and pulling the CG thru a 45° angle.
The IC acts like a moment arm or level. It should remain in one location. The farther to the front the instant center the less the IC location will change during rear end movement up and down / sideways during cornering and acceleration. The shorter the IC distance of frt mount point to is the to rear top link mount point the dartier the car will be because the IC is moving more and makes the car feel unsteerable to the driver. In side view, the lines of constant percent anti-squat all pass through the rear tire patch. The greater the slope, the higher the percentage of anti-squat. The location of the IC is determined by the intersection of 2 lines; one drawn through the pivot points of the upper link and the other drawn through the pivot points of the lower link. When the lower link is kept horizontal (or nearly so) and IC adjustments are made with the upper link, a raising of the front of the upper link causes the intersection of the link lines to move forward and fall on a line of less percent anti-squat; a lowering of the front of the upper link causes the intersection to move backward and fall on a line of greater percent anti squat.
So, a shorter IC...UNDER THE CONDITIONS JUST DESCRIBED...would move the anti squat value closer to...or perhaps in excess of...100%. At values over 100%, the car is said to have more bite or grip.
With a longer IC, there is less anti squat and the rear of the car is seen to squat on launch. The front of the car will always rise, of course, but that visible squat at the rear is accompanied by additional rise at the front. This additional rise is the result of a low anti squat value and NOT the result of the long IC.
IC length and the COG - Remember, our goal is to use lift to counteract weight transfer and plant the rear tires with downforce on acceleration.
Let's say your IC length is directly under your C/G location. This makes lifting the front of the car relatively easy. Moving the IC forward of the C/G location makes it much harder to gain lift at the rear due to the angle between the C/G and the IC, no matter how close you are to the neutral (100%) line.
One time we had a top link that was anchored to the chassis by the drivers right foot..LLLLLoooonnngg bar. Basically that is the only benefit. Less IC migration with longer top link. Top link down hill angle is between 5 and 7 degrees. On asphalt cars with sticky tires Lower links should be level with the pavement and longer is better here too. 20 “ typical , 24” is better. Hard spec tires means you have to add angle to the lower arms. Emods with hard spec tires need more bite and 5 degree up hill is typical. More than 5 degrees will promote quick hook up but not maintain grip down the straights as well and the 5 degree is a good compromise to grip off the turn and not wear out the rear tires.Illustrations from Herb Adams book Chassis Engineering – excellent read
Personally , I am not into ANTI anything on a race car. Adding in Anti Dive, anti squat, droop limiters etc.. to a poor performing race car to keep it from pushing is at best a Band-Aid if you think about it ...you are trying to treat the problem not the cause. I am a big believer in using a cars suspension to deal with weight transfer. I don't even like roll steer but in some classes, its all you can do to make the most with a bad situation. We all know why unsprung weight is so evil. You cannot control it. So, with that line of thought, sprung weight is " good" because we can control it..right? So how best to control the weight transfer? Springs and shocks and ARB (sway bar). Remember, Too much anti squat means BRAKE HOP
Above is 10 year old statement and you can teach an old dog new tricks..I believe in roll rear steer big time now. And if your rules dictate hard spec tires, look at anti squat. Not so much on sticky tire classes.
Draw a horizontal line thru the COG parallel with the ground
On front end, draw a vertical line from the ground thru the front axle center up to horizontal COG line. Now at this point, draw a line to the rear tire contact patch.
This is the 100% anti squat line. You want your rear IC at this line or a little over it.https://www.google.com/search?clien...placement#kpvalbx=_u5OfYbeLN4aYptQPjYewuAU121
If the IC is on the line connecting the rear tire patch with a line between the CG and the front axle centerline you have 100% anti squat. If the line falls below this point you have less than 100% anti squat. Study the illustration.
Study the attached. Less anti squat means the forces are pushing toward the front of the car by pulling at the CG at a 40° angle. The plus anti squat vector pushes to lift the front end and pulling the CG thru a 45° angle.
The IC acts like a moment arm or level. It should remain in one location. The farther to the front the instant center the less the IC location will change during rear end movement up and down / sideways during cornering and acceleration. The shorter the IC distance of frt mount point to is the to rear top link mount point the dartier the car will be because the IC is moving more and makes the car feel unsteerable to the driver. In side view, the lines of constant percent anti-squat all pass through the rear tire patch. The greater the slope, the higher the percentage of anti-squat. The location of the IC is determined by the intersection of 2 lines; one drawn through the pivot points of the upper link and the other drawn through the pivot points of the lower link. When the lower link is kept horizontal (or nearly so) and IC adjustments are made with the upper link, a raising of the front of the upper link causes the intersection of the link lines to move forward and fall on a line of less percent anti-squat; a lowering of the front of the upper link causes the intersection to move backward and fall on a line of greater percent anti squat.
So, a shorter IC...UNDER THE CONDITIONS JUST DESCRIBED...would move the anti squat value closer to...or perhaps in excess of...100%. At values over 100%, the car is said to have more bite or grip.
With a longer IC, there is less anti squat and the rear of the car is seen to squat on launch. The front of the car will always rise, of course, but that visible squat at the rear is accompanied by additional rise at the front. This additional rise is the result of a low anti squat value and NOT the result of the long IC.
IC length and the COG - Remember, our goal is to use lift to counteract weight transfer and plant the rear tires with downforce on acceleration.
Let's say your IC length is directly under your C/G location. This makes lifting the front of the car relatively easy. Moving the IC forward of the C/G location makes it much harder to gain lift at the rear due to the angle between the C/G and the IC, no matter how close you are to the neutral (100%) line.
One time we had a top link that was anchored to the chassis by the drivers right foot..LLLLLoooonnngg bar. Basically that is the only benefit. Less IC migration with longer top link. Top link down hill angle is between 5 and 7 degrees. On asphalt cars with sticky tires Lower links should be level with the pavement and longer is better here too. 20 “ typical , 24” is better. Hard spec tires means you have to add angle to the lower arms. Emods with hard spec tires need more bite and 5 degree up hill is typical. More than 5 degrees will promote quick hook up but not maintain grip down the straights as well and the 5 degree is a good compromise to grip off the turn and not wear out the rear tires.Illustrations from Herb Adams book Chassis Engineering – excellent read
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If we work thur the Figure 9-8 we see the same vector made up of horizontal and vertical forces like on the dog chain below. Assume the tires project 100 pounds force. Disregard effects of anti squat on downforce load for the purpose of understanding. More anti squat acting on 45° angle means Vert. Force of 71 lbs and Hor. Force of 71 lbs. With the forces acting thru the 40° less anti squat vectors we have Vert. Force of 64 lbs. and Horz. Force of 76 lbs.
Example of way over 100% anti squat is a drag car doing a wheelie off the christmas tree. Anti squat trys to lift the front of the race car
Below from www.physicsclassroom.com
Determining the Components of a Vector
The task of determining the amount of influence of a single vector in a given direction involves the use of trigonometric functions. The use of these functions to determine the components of a single vector was also discussed in Lesson 1 of this unit. As a quick review, let's consider the use of SOH CAH TOA to determine the components of force acting upon Fido. Assume that the chain is exerting a 60 N force upon Fido at an angle of 40 degrees above the horizontal. A quick sketch of the situation reveals that to determine the vertical component of force, the sine function can be used and to determine the horizontal component of force, the cosine function can be used. The solution to this problem is shown below.
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3/8 mile paved track late model BBSS setup
This email was sent to me and driver wants to have it posted to help other racers. I am keeping his name and address private but thank him for permitting the sharing of this project. We will be going thru the set up process changing from a ½ mile track package to a 3/8 mile setup. Driver walked the 3/8 track and majority of cars there are BBSS so the track is not that bumpy to take air off the car. Note - you do not need the latest greatest new chassis to be super competitive.
Note this is a Big Bar Soft Spring setup.
He says -
I have a ~2005 Port City straight rail asphalt
Late Model. It is a BBSS chassis.
Here is how the car was setup to run a ½ mile asphalt track with sweeping flat turns. The car turned its fastest lap ever with this setup and was on rails. The car was scaled after the race (topped off fuel). Here are those numbers;TOTAL WEIGHT = 2702 lbs.
% Left = 57.8
% Rear = 49.8
% Diagonal = 55.2
*Swaybar Unhooked
RIDE HEIGHTS
LF = 4" RF = 4" RR = 4-1/2" LR= Floats
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 713 lbs (26.4%) 180 lb spring. Camber +5½°
Caster +2°
RF = 642 lbs (23.8%) 185 lb spring. Camber -1½°
Caster +4°
LR = 850 lbs (31.5%) 225 lb spring.
RR = 497 lbs (18.4%) 400 lb spring.
SWAY BAR
1⅜" splined w/ 13" arms. Calculated @ ~532 lb.
SHOCKS
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LATE MODEL 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
************Going forward, I will be racing this car on a ⅜ mile asphalt track. The whole track has 12° banking. The radius of both turns is ~161', which would be a diameter of ~322'.
Would you be able to put together a baseline setup package for this track?
Ie. Spring rates that will work with my 1⅜" sway bar (which I calc'ed at a rate of ~ 532 lbs), camber, caster, etc.
3/8 mile track rules - American Racer tires AR153 10 inch slicks
-Total weight will be Increasing to 2800 lbs. in 2022
- NO bump stops.
- 4" ride height.
- 58% max left side weight.***CURRENT CHASSIS CONFIGURATION***
NOV 27, 2021
Take note these numbers are with INCORRECT TIRE STAGGER. These numbers are with;
Front Stagger = 2¾"
Rear Stagger = 2½"
This was the only combination I had available.
One of the top teams suggested I run;
1½" FRONT STAGGER.
3" REAR STAGGER.
I previously did the math and 3" rear
stagger is about right.
TOTAL WEIGHT "RACE READY" = 2747 lbs.
Left = 57.0% (1567 lbs)
Rear = 49.3% (1357 lbs)
Diagonal = 54.2%* (1491 lbs)
*Swaybar Preloaded one (1) turn
LR BITE +311 lbs
FRAME RIDE HEIGHTS:
LF = 4" RF = 4"
LR= ~4" (floats) RR = 4-1/2"
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 733 lbs (26.7%) 180 lb spring. Camber +5½°
Caster +2°
RF = 657 lbs (23.9%) 185 lb spring. Camber -3°
Caster +4°
LR = 834 lbs (30.4%) 225 spring rate
RR = 523 lbs (19.0%) 400 spring rate
SWAY BAR
1⅜" DIAMETER, SPLINED.
3 PIECE W/13" ARMS.
CALCULATED @ ~532 LBS.
SHOCKS (BILSTEIN)
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LM 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
TIRE PRESSURES COLD
LF = 12 psi
RF = 18 psi
LR = 10 - 12 psi
RR = 18 psiInitially, my final rear gear ratio will be 6.02.
I do expect that to change.
A 6600 RPM rev limiting chip is currently installed. Could go to 7000 RPM in the future. Any more would be pushing past what the camshaft has to offer. No sense in beating a dead horse!
This email was sent to me and driver wants to have it posted to help other racers. I am keeping his name and address private but thank him for permitting the sharing of this project. We will be going thru the set up process changing from a ½ mile track package to a 3/8 mile setup. Driver walked the 3/8 track and majority of cars there are BBSS so the track is not that bumpy to take air off the car. Note - you do not need the latest greatest new chassis to be super competitive.
Note this is a Big Bar Soft Spring setup.
He says -
I have a ~2005 Port City straight rail asphalt
Late Model. It is a BBSS chassis.
Here is how the car was setup to run a ½ mile asphalt track with sweeping flat turns. The car turned its fastest lap ever with this setup and was on rails. The car was scaled after the race (topped off fuel). Here are those numbers;TOTAL WEIGHT = 2702 lbs.
% Left = 57.8
% Rear = 49.8
% Diagonal = 55.2
*Swaybar Unhooked
RIDE HEIGHTS
LF = 4" RF = 4" RR = 4-1/2" LR= Floats
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 713 lbs (26.4%) 180 lb spring. Camber +5½°
Caster +2°
RF = 642 lbs (23.8%) 185 lb spring. Camber -1½°
Caster +4°
LR = 850 lbs (31.5%) 225 lb spring.
RR = 497 lbs (18.4%) 400 lb spring.
SWAY BAR
1⅜" splined w/ 13" arms. Calculated @ ~532 lb.
SHOCKS
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LATE MODEL 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
************Going forward, I will be racing this car on a ⅜ mile asphalt track. The whole track has 12° banking. The radius of both turns is ~161', which would be a diameter of ~322'.
Would you be able to put together a baseline setup package for this track?
Ie. Spring rates that will work with my 1⅜" sway bar (which I calc'ed at a rate of ~ 532 lbs), camber, caster, etc.
3/8 mile track rules - American Racer tires AR153 10 inch slicks
-Total weight will be Increasing to 2800 lbs. in 2022
- NO bump stops.
- 4" ride height.
- 58% max left side weight.***CURRENT CHASSIS CONFIGURATION***
NOV 27, 2021
Take note these numbers are with INCORRECT TIRE STAGGER. These numbers are with;
Front Stagger = 2¾"
Rear Stagger = 2½"
This was the only combination I had available.
One of the top teams suggested I run;
1½" FRONT STAGGER.
3" REAR STAGGER.
I previously did the math and 3" rear
stagger is about right.
TOTAL WEIGHT "RACE READY" = 2747 lbs.
Left = 57.0% (1567 lbs)
Rear = 49.3% (1357 lbs)
Diagonal = 54.2%* (1491 lbs)
*Swaybar Preloaded one (1) turn
LR BITE +311 lbs
FRAME RIDE HEIGHTS:
LF = 4" RF = 4"
LR= ~4" (floats) RR = 4-1/2"
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 733 lbs (26.7%) 180 lb spring. Camber +5½°
Caster +2°
RF = 657 lbs (23.9%) 185 lb spring. Camber -3°
Caster +4°
LR = 834 lbs (30.4%) 225 spring rate
RR = 523 lbs (19.0%) 400 spring rate
SWAY BAR
1⅜" DIAMETER, SPLINED.
3 PIECE W/13" ARMS.
CALCULATED @ ~532 LBS.
SHOCKS (BILSTEIN)
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LM 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
TIRE PRESSURES COLD
LF = 12 psi
RF = 18 psi
LR = 10 - 12 psi
RR = 18 psiInitially, my final rear gear ratio will be 6.02.
I do expect that to change.
A 6600 RPM rev limiting chip is currently installed. Could go to 7000 RPM in the future. Any more would be pushing past what the camshaft has to offer. No sense in beating a dead horse!
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Driver did not know where the front Roll Center was so he bought a software package and measured it. Was 1.7 inch height and located 4.5 inch to the right of car centerline. This meant the car was a rocket for a few laps then fell off due to heat build up on tires. The jacking effect carried the left front tire thru the turns like the old Modifieds did with the straight axle. Super cool to watch but not the " hot setup".
Driver is working on benchmarking the car and correcting the roll centers.
Driver is working on benchmarking the car and correcting the roll centers.
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Driver went and rechecked his work. found the Front roll center was really 3.5 inch height. This is a wet sump engine with iron heads so 2.5" is about the max height. We have spec slicks on 12° track so we need vertical downforce not shear force. A lower RC will give us this. BBSS means we do not have a lot of body roll but, the body will provide some downforce by downloading on the right front tire ( momentum in the turn). Where else will the momentum go? From the COG thru the RC and to the right front tire and sideways in shear. The trick is to use the downforce to plant the Rt ft tire with proper ARB (sway bar) and springs.
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Steve Smith in his great book Paved Track Big Bar Soft Sprig Setups outlined the whole thing. Buy the book.
He states you need Anti-dive which is 3 1/2 to 4 ° on right front and 1 1/2 to 2 ° on left front. I can almost guarantee you that you are running an after market chassis like Howe or Port City, the lower A-arm mounts are parallel to the track (same height front and back).
You need the right front upper A-arm mount point on the front 1/2" higher than the rear (HEIGHT FROM THE GROUND)
you need the left upper A-arm mounts so that the front mount is 1/4" higher than the rear
The left has less anti-dive than the right so forward load transfer compresses the left front corner easier than the right and it does it quicker, helps place weight on the left front tire at corner entry. Shock rebound at left front and stiffer right rear spring help hold down the left front. If we use a right front compression shock it holds cross weight and we have a push. Note in photo the lever distance of IC to COG.
My opinion is that a mechanical means to handle momentum (aka weight transfer) is far better than high dollar shocks and labor intensive spring swaps. This is why we need to tackle this first then fix the roll center location.
He states you need Anti-dive which is 3 1/2 to 4 ° on right front and 1 1/2 to 2 ° on left front. I can almost guarantee you that you are running an after market chassis like Howe or Port City, the lower A-arm mounts are parallel to the track (same height front and back).
You need the right front upper A-arm mount point on the front 1/2" higher than the rear (HEIGHT FROM THE GROUND)
you need the left upper A-arm mounts so that the front mount is 1/4" higher than the rear
The left has less anti-dive than the right so forward load transfer compresses the left front corner easier than the right and it does it quicker, helps place weight on the left front tire at corner entry. Shock rebound at left front and stiffer right rear spring help hold down the left front. If we use a right front compression shock it holds cross weight and we have a push. Note in photo the lever distance of IC to COG.
My opinion is that a mechanical means to handle momentum (aka weight transfer) is far better than high dollar shocks and labor intensive spring swaps. This is why we need to tackle this first then fix the roll center location.
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Measured the Port City chassis. As found the front top A-Arm mounts were taller in the rear than the front (mount points relative to ground) exactly what we do not want for anti-dive. Fixed these and roll center now off big time as expected. Front roll center now 2.1" height and offset 14.2" to the left of centerline.
After playing with the Circle Track Analyzer the new Roll Center is 2.4" height and 2.9" offset to the right and looks pretty good in 2" dive, 1/2° roll. Got this by adding height to the ball joints.
After playing with the Circle Track Analyzer the new Roll Center is 2.4" height and 2.9" offset to the right and looks pretty good in 2" dive, 1/2° roll. Got this by adding height to the ball joints.
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Why we need rear roll over steer
Note the left figure below is standard Port city set up with rear end square to the car centerline.
The right figure is a rear steer car and note the turning radius is a lot shorter axis.
Roll over steer allows the car to roll around a corner without breaking traction. Breaking traction occurs when forward grip stops and the tire goes into shear sliding sideways. This is one reason you use Stagger and it helps to a point. But at some point all locked rear ends lose traction and you have to hit the brakes or spin out. With no rear roll steer the tire has to break traction to turn. When you have roll over steer the rear end steers the car and no side slip is required. Forward traction is maintained and the rear end is steered.
When I see two famous car book authors Steve Smith ( his illustrations and my sketched up mess) and Herb Adams ( his scan of page in Chassis Engineering) say in print that this works, I have to believe it. Even more than that, just look at a dirt late model race. You can see the wheelbase shrink on the drivers side with body roll.
My sketched up illustrations are very simplified. I should draw in the 26° axle angle of the right side wheel but you get the idea. Shorter turn radius and pivot turn point a lot closer to the COG means better turning relative to the competition.
Note the left figure below is standard Port city set up with rear end square to the car centerline.
The right figure is a rear steer car and note the turning radius is a lot shorter axis.
Roll over steer allows the car to roll around a corner without breaking traction. Breaking traction occurs when forward grip stops and the tire goes into shear sliding sideways. This is one reason you use Stagger and it helps to a point. But at some point all locked rear ends lose traction and you have to hit the brakes or spin out. With no rear roll steer the tire has to break traction to turn. When you have roll over steer the rear end steers the car and no side slip is required. Forward traction is maintained and the rear end is steered.
When I see two famous car book authors Steve Smith ( his illustrations and my sketched up mess) and Herb Adams ( his scan of page in Chassis Engineering) say in print that this works, I have to believe it. Even more than that, just look at a dirt late model race. You can see the wheelbase shrink on the drivers side with body roll.
My sketched up illustrations are very simplified. I should draw in the 26° axle angle of the right side wheel but you get the idea. Shorter turn radius and pivot turn point a lot closer to the COG means better turning relative to the competition.
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We found out the top link mounting point on the rear end was same setting as from the Port City factory. We are running 58% left side weight so the distance from right rear tire centerline to tip link mount was off 6". since we can only use solid links , no springer top link or spring trailing arms, the mount location is vital to good tire hook up. As found distance from rt rear CL was 32" on 66" rear track width. So 58% left side weight means the mount point is 66 x .58 = 38.25" and changing it means both rear tires are loading the same.
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UFO
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Hi RM I think with the top link or pull bar setup, it acts similar to a torque arm. On a TA rear, if you have live birdcages, the balanced load setup would have the front mount point of the TA on a line starting at a point where a line projected back from the CG, square to the rear, meets the front to back center of the rear. The other point defining the line is a point on a transverse line from the CG, to the right with the distance from that point to the CG being equal to the distance from the CG to center of the rear, times the gear ratio of the rear. Any mount point on that line should load the tires proportionally to the left side percentage. The difference with the pull bar is the upward vector at the front would not be the same and would vary with the angle and the vertical distance between the pull bar mount point on the rear, to the lower trailing arm mount points. I think a drawing would explain this better, but I don't have time right now.
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not replying (see previous page).
nuff said!
nuff said!
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UFO
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Sorry, there is a mistake in the previous post. The transverse or lateral distance should be the distance from the CG to the axle centerline, times 1 over the gear ratio. lateral distance = CG to rear / gear ratio
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drobbie
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Ranger Mike,
I was reading through your posts on rear steer and can say I am with you on it having a positive effect on cornering. We experimented with it late last season and found good results. What I am now curious about is when making the adjustments for rear steer is it better to make the adjustments at the rear end or at the chassis. In other words does raising the front of the trailing arms (chassis mounts) have a different effect than raising or lowering the rear of the trailing arms (rear mounts)
Thanks
I was reading through your posts on rear steer and can say I am with you on it having a positive effect on cornering. We experimented with it late last season and found good results. What I am now curious about is when making the adjustments for rear steer is it better to make the adjustments at the rear end or at the chassis. In other words does raising the front of the trailing arms (chassis mounts) have a different effect than raising or lowering the rear of the trailing arms (rear mounts)
Thanks
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i have not studied the benefit/drawback to adjusting on front chassis mount vs rear end mounts. If the rules let you adjust in rear roll steer then go with the easiest accessible adjustment. Now if the rules are more stringent, and not clearly telling you that you can do this, (Smokey Yunick) then you have to be a little bit clandestine in dialing in this advantage. You can buy offset bushings. You can grind in a slot to give this adjustment and the large washer should cover it up. Depends. But having the ability to have a wheelbase change is a definite winner!
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cearnold23
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Mike,
I am working with a suspension that has a modified watts link to located the rear axle in the car longitudinally (sprint car) and no one in the business can tell me how to locate the instant center. As i understand it with this style of suspension the IC move drastically as the suspension travels. I have looked for programs to find it but have come up empty. Any insight on have to find the IC would be greatly appreciated
Thanks
I am working with a suspension that has a modified watts link to located the rear axle in the car longitudinally (sprint car) and no one in the business can tell me how to locate the instant center. As i understand it with this style of suspension the IC move drastically as the suspension travels. I have looked for programs to find it but have come up empty. Any insight on have to find the IC would be greatly appreciated
Thanks
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Why you worried about the IC ?? Look at the rear roll center!
The part about the IC moving drastically , to me, does not matter. The RC will be more stable than the Panhard bar setup.
The Roll Center of the Watts linkage is the center point mount of the Center Link. This set up eliminates the slight lateral movement that the panhard bar has. The watts is a better deal for straight line control from a design standpoint. James Watt invented this when he made the first practical steam engine.
It is a more complex set up (and heavier) because the main pivot point is the roll center height and is not easily changed.
Pic is from Circle Track Suspension by Forbes Aird , i got a copy at Jegs or go on line Motorbooks International, Powerpro Series
The part about the IC moving drastically , to me, does not matter. The RC will be more stable than the Panhard bar setup.
The Roll Center of the Watts linkage is the center point mount of the Center Link. This set up eliminates the slight lateral movement that the panhard bar has. The watts is a better deal for straight line control from a design standpoint. James Watt invented this when he made the first practical steam engine.
It is a more complex set up (and heavier) because the main pivot point is the roll center height and is not easily changed.
Pic is from Circle Track Suspension by Forbes Aird , i got a copy at Jegs or go on line Motorbooks International, Powerpro Series
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cearnold23
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I need to know the IC bc we are using the watts link in place of a 4 link.
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http://performancetrends.com/SuspAnzr.htm
this may be your best tool. call Kevin at performance trends
this may be your best tool. call Kevin at performance trends
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UFO
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cearnold23,
On a true watts link, with equal length rods, there is no IC because the center pivot is a straight line motion that is perpendicular to the rods when they are positioned parallel to each other.
On a true watts link, with equal length rods, there is no IC because the center pivot is a straight line motion that is perpendicular to the rods when they are positioned parallel to each other.
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cearnold23
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Unfortunately this is not equal length rods.
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that is NOT a Watts linkage. It is a swing arm suspension. Sometimes called a Z link. As far as this photo shows me. I can not see all the workings of it but appears to be a variation of the swing arm with torsion bar.
I suggest you buy I.M.C.A. Modified Racing Technology from Steve Smith Autosports. he has good intial settings outlined in it.
I suggest you buy I.M.C.A. Modified Racing Technology from Steve Smith Autosports. he has good intial settings outlined in it.
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Hiredgun161
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this is quite similar to the setup i run in my 04 port city, exception by track rules the front springs have to be a minimum of 325 to get a hundred pound weight break.Ranger Mike said:
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