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forgive me WN9..some times do not remember if I discussed this point..let me write up the bench mark process and will post soon.
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
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WN9Y
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Maybe you did, I maybe overlooked it. But, thank you in advance. It's been a fun project, looking forward to your post.
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Rebel42
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thanks for getting back with me, and i hope you find your old notes on what parts are interchangable for the better. are track has made some new engine rules this year, and with making are class faster i know i need to make the chassis handle more speed. we use to run 10inch wheels and that really helped, but now the inspectors have made it clear that we can only run the 8inchers.
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Why change spindles? it' s all about tires. You want to maintain the most tire contact and controlling camber change is the solution. Shorter Spindles ( all else being the same) will lower the Roll Center and reduce camber change. See post 4 to 7 above and look at post 13 diagram. Please read the posts on why roll center height and location are so important in round track racing. The Impala spindles are the " hot set up " on a metric chassis. Big Chevy Impala and Caprice 1980 to 1994 casting number is 369056 for right side and 396055 for left side and if you can not locate these I can send you info on other substitutes. They are 6 pound lighter got 1 inch wide x 12 inch rotor and 5 x 5 bolt circle.
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One of the most frustrating things I found in racing was shear ignorance of some people who ought to know better. The monkey see monkey do phenomena is alive and well at the short tracks and its every where. for the young racer coming up the quicker you learn this and the faster you grasp the basics , the better off you will be..to include dealing with life's frustrations..Enough of this philosophy b.s.
We bench mark a race car to establish a measurable base line. Racing is a constant adjustment process. on any given day the track will change and you have to adjust for this condition. Add in competitive changes to improve performance and you are constantly working on the set up. Races are won buy the driver and crew that can negotiate the course the fastest and FINISH ahead of the rest. When you are adjusting many things ( only one adjustment at a time is the rule...right.. like that's going to happen) you have changes things from the base line. What happens if you get punted and hit the wall and have to swap out suspension parts? Back to base line and add in adjustments you made to the point you got wrecked.
We are going to bench mark the car to measure all settings and make are record so we can make logical adjustments that will give us better performance than the other guy.
Get some white poster boards from the drug store or Wal-Mart. You will have to tape a few sheets together so you have enough area cover both front tires and frame mount points when you drop a plumb bob from the upper and lower frame mount points in the front. We are not going too deep into the suspension and will not worry about the upper and lower A-arm rear mount points.
Start with the car fueled up, tires inflated, in full race trim and it helps if you can get the neighbor hood fat kid to sit in the drivers seat while you are measuring things. In my case I got some Massey Ferguson tractor weights that equaled the drivers weight..(and some said IQ but I digress). We need to establish a vehicle center line. I use the mid point of the track width ( mid point of the tread ) and mark this on the paper.
What we are going to do is measure and record the vehicle center line. We are going to measure the length of all A-Arms from the frame mount point to the center of ball joint AS VIEWED FROM THE FRONT OF THE CAR. This length may not necessarily be the length of the A-arm. In other words the distance between these two points as intersected by a plane parallel with the floor.
We are going to measure and record the height from the floor and distance from vehicle centerline of each ball joint center, spring pad center or coil over mount point center and A-arm frame mount center point. On strut cars we have to do the same for upper and lower strut height and location , lower BJ and upper and lower spring pads if applicable. When complete we will use the Circle Track Analyzer from Performance Trends to see where the Roll Center is and go from there..More later. out of beer..
Rebel and WN9 ...i am counting on you guys to send me the data once I finish this post so we can see where things are on both your cars..send me private message if you prefer not to post..
We bench mark a race car to establish a measurable base line. Racing is a constant adjustment process. on any given day the track will change and you have to adjust for this condition. Add in competitive changes to improve performance and you are constantly working on the set up. Races are won buy the driver and crew that can negotiate the course the fastest and FINISH ahead of the rest. When you are adjusting many things ( only one adjustment at a time is the rule...right.. like that's going to happen) you have changes things from the base line. What happens if you get punted and hit the wall and have to swap out suspension parts? Back to base line and add in adjustments you made to the point you got wrecked.
We are going to bench mark the car to measure all settings and make are record so we can make logical adjustments that will give us better performance than the other guy.
Get some white poster boards from the drug store or Wal-Mart. You will have to tape a few sheets together so you have enough area cover both front tires and frame mount points when you drop a plumb bob from the upper and lower frame mount points in the front. We are not going too deep into the suspension and will not worry about the upper and lower A-arm rear mount points.
Start with the car fueled up, tires inflated, in full race trim and it helps if you can get the neighbor hood fat kid to sit in the drivers seat while you are measuring things. In my case I got some Massey Ferguson tractor weights that equaled the drivers weight..(and some said IQ but I digress). We need to establish a vehicle center line. I use the mid point of the track width ( mid point of the tread ) and mark this on the paper.
What we are going to do is measure and record the vehicle center line. We are going to measure the length of all A-Arms from the frame mount point to the center of ball joint AS VIEWED FROM THE FRONT OF THE CAR. This length may not necessarily be the length of the A-arm. In other words the distance between these two points as intersected by a plane parallel with the floor.
We are going to measure and record the height from the floor and distance from vehicle centerline of each ball joint center, spring pad center or coil over mount point center and A-arm frame mount center point. On strut cars we have to do the same for upper and lower strut height and location , lower BJ and upper and lower spring pads if applicable. When complete we will use the Circle Track Analyzer from Performance Trends to see where the Roll Center is and go from there..More later. out of beer..
Rebel and WN9 ...i am counting on you guys to send me the data once I finish this post so we can see where things are on both your cars..send me private message if you prefer not to post..
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- #286
mender
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Is he racing in Australia?Ranger Mike said:
Another thing that helps with a strut FWD car is to put in lots of caster to make up for the limited camber adjustment on most of these cars. If the driver is comfortable with trailing throttle oversteer, keep increasing the rear roll resistance until the car is only a little pushy with throttle on. Biasing the front brakes can crutch the turn-in enough to get to mid-corner where the driver can switch to throttle. Left foot braking helps.
Do the mods in that order.
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excellent..This FWD racing not my strong suit..thanks Menfer
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WingedOver
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Nice post man! I've read all of the books you have mentioned throughout my younger years and they kind of helped push me more towards being a engineer. I'm in mechanical at la tech right now trying to balance the course load with racing a sprint car when my shop is 2 hours away! Not fun... ok maybe a little!
Anyway just wanted to commend you for the post, pretty interesting stuff here.
Anyway just wanted to commend you for the post, pretty interesting stuff here.
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Welcome and thank you. There are so many high quality people contributing...a world in fact..this whole Physics forum is like having every possible experts in the world available and all you have to do is ASK... best kept secret on the internet..
look forward to hearing about your car
rm
look forward to hearing about your car
rm
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- #291
rce4csh
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Mr. Mike, can you expand on the construction and use of your fabricated traverse bar? I. like many others, am looking to ease the whole set up procedure to effectively reduce the amount of time and effort spent on the mundane work so as to get to the "meat of the matter." Time spent messing with jackstands and strings, the neighbor's dog who came to visit adjusting your strings, back and forth on the caster/camber/turn plate deal, etc. is time that could better spent on the tiny details that make for lower lap times. More time to spend on the shock dyno, more efforts at the "what ifs" in software geometry analysis and so on.
In my mind and at my age, I am leaning toward a take down fixture with enough accuracy that it can easily be set up in the hotel parking lot, adjusted to accommodate pavement irregularities and will allow you to get the bulk of your critical squaring, caster camber, toe, bump, etc done with the suspension basically locked ( blocking, fixed links, add on fixtures. etc.) and the obstacles (tires) out of the way. Following this, the balance of scaling operations with the car reassembled. The specific details of procedure can be finalized when the details and use of traverse bar is refined.
On another note as to why this sort of thing is important; anyone here notice the drop off in interest in part time crew help? Seriously, I have noticed a strong trend in the last six years where race car help is becoming more difficult to obtain. The poor economy further fuels this problem as people who are likely to help, think twice about their out of pocket expenses in doing so. Also, the sheer number of diversions and intrusions on a person's time makes getting the appropriate amount of time spent on the race car harder to accomplish. That is why time spent here is so important. A good understanding of what to achieve coupled with refined and expedient ways to achieve them with less people power saves time for other activities needed to make things go fast...including beer, pork rhines...and the occasional romantic endeavor. The later done to maintain clear thinking and refine one's personal style!
In my mind and at my age, I am leaning toward a take down fixture with enough accuracy that it can easily be set up in the hotel parking lot, adjusted to accommodate pavement irregularities and will allow you to get the bulk of your critical squaring, caster camber, toe, bump, etc done with the suspension basically locked ( blocking, fixed links, add on fixtures. etc.) and the obstacles (tires) out of the way. Following this, the balance of scaling operations with the car reassembled. The specific details of procedure can be finalized when the details and use of traverse bar is refined.
On another note as to why this sort of thing is important; anyone here notice the drop off in interest in part time crew help? Seriously, I have noticed a strong trend in the last six years where race car help is becoming more difficult to obtain. The poor economy further fuels this problem as people who are likely to help, think twice about their out of pocket expenses in doing so. Also, the sheer number of diversions and intrusions on a person's time makes getting the appropriate amount of time spent on the race car harder to accomplish. That is why time spent here is so important. A good understanding of what to achieve coupled with refined and expedient ways to achieve them with less people power saves time for other activities needed to make things go fast...including beer, pork rhines...and the occasional romantic endeavor. The later done to maintain clear thinking and refine one's personal style!
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- #292
flashpuppy
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First post to the site. I have been going through this thread for about two weeks now, but I have a few questions. I'm building a little street rod and am having some trouble deciding on what to do for rear suspension. I am using a ton of circle track parts on this and wouldn't mind sticking with that style of rear suspension. The thing weighs around 1950lbs wet + 200 for me, SBC, TKO600 manual trans, Winters Quick-Change, front suspension is based off of a "Rayburn" car.
What would some of you guys be looking at and considering for this? I'm kinda leaning towards a torque-link setup right now or maybe a triangulated four-link? Thoughts? What else do you need from me?
Here's a quick pic for S&G's:
What would some of you guys be looking at and considering for this? I'm kinda leaning towards a torque-link setup right now or maybe a triangulated four-link? Thoughts? What else do you need from me?
Here's a quick pic for S&G's:
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rce4csh ..the whole point of the traverse gage was to provide a quick easy to use set up to measure any changes ( via sudden impact with the 3rd turn wall, other cars etc..)
problem is it was bulky, and only measured one side at a time. I sold industrial lasers at one time in my seedy and questionable career and played with the idea of using a couple of rifle bore scope lasers to replicate the string procedure. Note attached sketch..
we need to fabricate a reference datum made 1" x 1" mild steel tubing. We have to mount this inside the cockpit as mounting it underneath the car can be a problem due to headers and the like. the mount locations could be roll bar gussets drilled to mount the stand off bars that connect to the reference bar. The reference bar would have a plate welded on each end to accept the bore scope laser block.
Bore scope Laser block - This block can be rotated and locked into position through out 360 degrees rotation. It has 4 flat sides and a small spirit level can be placed on it to level to earth. Now we have a means of doing quick chassis checks anywhere.
The mounts and blocks should be as square as possible and marked for mounting.. i.e. once you mount this make sure each time the bar is mounted the same and that way the right side laser will be on the right side..etc.
How it works- You have to string the car as described in the previous post. Place the spirit level on the block and level it. This should spot the laser on the garage floor as perpendicular as possible. This is the right side bench mark. Place a piece of masking tape there and mark the dot with a felt tip marker. Now you can spot the laser dot at the ground in front of the right front wheel at the location you have marked after using the sting method to determine the proper location. You are simply recording the distance from the bench mark to this point so you ca repeat this in the future without having to string the car.
If you really want to save time you can fabricate a " square " for each wheel which is simply a 4" x 4" block of wood trued up to square that has a center line scribed on it and is the exact height of the spindle center line or axle center line. Instead of one laser dot at the wheel location you record two or three and scribe a line on the masking tape. Then you place the " square" on the masking tape and center the scribe line of the square to the spindle center line. Now you can record the distance from the bench mark and you have your set up for that wheel.
BUT.. you are at the mercy of an unknown garage floor surface and things get squirrley when you project " squareness " from a non true surface.don't forget the car should be in race trim and same ride height. It would help greatly if you used a set of wheels and tires ( we painted our red) that was used for this. That way we knew the stagger was the same and the wheels were not bent.
I am sure the active minds on this forum will skull this out and come up with other innovative solutions...
problem is it was bulky, and only measured one side at a time. I sold industrial lasers at one time in my seedy and questionable career and played with the idea of using a couple of rifle bore scope lasers to replicate the string procedure. Note attached sketch..
we need to fabricate a reference datum made 1" x 1" mild steel tubing. We have to mount this inside the cockpit as mounting it underneath the car can be a problem due to headers and the like. the mount locations could be roll bar gussets drilled to mount the stand off bars that connect to the reference bar. The reference bar would have a plate welded on each end to accept the bore scope laser block.
Bore scope Laser block - This block can be rotated and locked into position through out 360 degrees rotation. It has 4 flat sides and a small spirit level can be placed on it to level to earth. Now we have a means of doing quick chassis checks anywhere.
The mounts and blocks should be as square as possible and marked for mounting.. i.e. once you mount this make sure each time the bar is mounted the same and that way the right side laser will be on the right side..etc.
How it works- You have to string the car as described in the previous post. Place the spirit level on the block and level it. This should spot the laser on the garage floor as perpendicular as possible. This is the right side bench mark. Place a piece of masking tape there and mark the dot with a felt tip marker. Now you can spot the laser dot at the ground in front of the right front wheel at the location you have marked after using the sting method to determine the proper location. You are simply recording the distance from the bench mark to this point so you ca repeat this in the future without having to string the car.
If you really want to save time you can fabricate a " square " for each wheel which is simply a 4" x 4" block of wood trued up to square that has a center line scribed on it and is the exact height of the spindle center line or axle center line. Instead of one laser dot at the wheel location you record two or three and scribe a line on the masking tape. Then you place the " square" on the masking tape and center the scribe line of the square to the spindle center line. Now you can record the distance from the bench mark and you have your set up for that wheel.
BUT.. you are at the mercy of an unknown garage floor surface and things get squirrley when you project " squareness " from a non true surface.don't forget the car should be in race trim and same ride height. It would help greatly if you used a set of wheels and tires ( we painted our red) that was used for this. That way we knew the stagger was the same and the wheels were not bent.
I am sure the active minds on this forum will skull this out and come up with other innovative solutions...
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Flashpuppy..
welcome..
i assume you have some kind of limited slip differential in the quick change..right?
coming up..rear end mounting , trailing arms etc..
welcome..
i assume you have some kind of limited slip differential in the quick change..right?
coming up..rear end mounting , trailing arms etc..
- #295
rick7343
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Hmmm... I typed out a lengthy post here in this forum yesterday and it said it was sent, but I don't see it anywhere...
I was looking for more info on stock rear 4 link trailing arm angles...
With stock brackets on the rearend at a 6" ride height, the lower arm runs downward to the frame mount... Better to run a higher ride height to get a level or or slightly upward angle, or can a longer bracket on the rearend help?
Can the rear end bracket be too long?
Or is it just the relationship between the upper and lower rear arms?
Affect on roll center by changing angles?
Rear roll center or center of gravity more important?
Mid banked 1/4 miles asphalt car... 3200lbs, 55%left, 50% rear, 8" towel city retreads, 13.5" crank height, 69 chevelle type chassis... Frame mounts have to be in the stock location except front uppers, we can adapt a Ford 9" so we can play there a bit...
Thanx! this forum is AWESOME!
I was looking for more info on stock rear 4 link trailing arm angles...
With stock brackets on the rearend at a 6" ride height, the lower arm runs downward to the frame mount... Better to run a higher ride height to get a level or or slightly upward angle, or can a longer bracket on the rearend help?
Can the rear end bracket be too long?
Or is it just the relationship between the upper and lower rear arms?
Affect on roll center by changing angles?
Rear roll center or center of gravity more important?
Mid banked 1/4 miles asphalt car... 3200lbs, 55%left, 50% rear, 8" towel city retreads, 13.5" crank height, 69 chevelle type chassis... Frame mounts have to be in the stock location except front uppers, we can adapt a Ford 9" so we can play there a bit...
Thanx! this forum is AWESOME!
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Rick..no you are not going crazy..you sent it as private message to me..thanks..i am working on reply but need to dog into notes ..have not go chance to get er done..yet..but i will
welcome to the forum ..
rm
welcome to the forum ..
rm
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rick7343
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DId I send you 2?
Thought I posted one and sent you message as well...
Thx...
Thought I posted one and sent you message as well...
Thx...
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Rear mount points and other rear end issues
read post # 253 on page 16 in this thread. for the 3 link definition
read post 132 on page 9 for the 4 link definition
read post 116 page 8 for the rear steer definition
I do not have any dimensions on the stock rear end angles and will have to check out Krash's sportsman metric chassis next time I am over there.
in general, I am opposed to raising the ride height for any reason.
if you read the post above, the 4 link lower links run slightly down hill ( 5 degrees) to the frame as you are.
I need you to clarify the rear end bracket you are describing..is it the trailing arm from rear end to frame?
Regarding the relationship between the upper and lower rear arms and effect on roll center by changing angles..
since you are severely limited by the rules there is not a whole lot you can do..BUT...there is a definite advantage by using eccentrics to adjust rear roll steer which should be legal by the rules..you may want to check this out. Personally, I believe the Roll center height and position are more important to changing the chassis performance. Rules dictate how low and how far back the engine can be. You are pretty much stuck with the 9 inch Ford rear end and its effect on CG..and earlier post noted fuel cell location. If you have reached 55 % left side and 50 % rear you just about reached the Max. as I assume you have to scale and meet this specs.
You are racing on hard tires in a very structured class. Big Horsepower is a waste since you can not hook it up on the rines you have to run on..My suggestions...run a two barrel carb, .. find the camber curve on the front and rear tires, eliminate bump steer, add in ackerman if possible, measure and understand the rear end eccentric that can crank in roll steer and use it.
note the eccentric from speedway motors..has 1/4 inch offset so...ifin you use one omn each arm you can crank in as much as 1/2 inch rear steer..don't know but if possible i would run 4..just thinking out loud.. if i could crank in an inch and really hook up..maybe a checker
read post # 253 on page 16 in this thread. for the 3 link definition
read post 132 on page 9 for the 4 link definition
read post 116 page 8 for the rear steer definition
I do not have any dimensions on the stock rear end angles and will have to check out Krash's sportsman metric chassis next time I am over there.
in general, I am opposed to raising the ride height for any reason.
if you read the post above, the 4 link lower links run slightly down hill ( 5 degrees) to the frame as you are.
I need you to clarify the rear end bracket you are describing..is it the trailing arm from rear end to frame?
Regarding the relationship between the upper and lower rear arms and effect on roll center by changing angles..
since you are severely limited by the rules there is not a whole lot you can do..BUT...there is a definite advantage by using eccentrics to adjust rear roll steer which should be legal by the rules..you may want to check this out. Personally, I believe the Roll center height and position are more important to changing the chassis performance. Rules dictate how low and how far back the engine can be. You are pretty much stuck with the 9 inch Ford rear end and its effect on CG..and earlier post noted fuel cell location. If you have reached 55 % left side and 50 % rear you just about reached the Max. as I assume you have to scale and meet this specs.
You are racing on hard tires in a very structured class. Big Horsepower is a waste since you can not hook it up on the rines you have to run on..My suggestions...run a two barrel carb, .. find the camber curve on the front and rear tires, eliminate bump steer, add in ackerman if possible, measure and understand the rear end eccentric that can crank in roll steer and use it.
note the eccentric from speedway motors..has 1/4 inch offset so...ifin you use one omn each arm you can crank in as much as 1/2 inch rear steer..don't know but if possible i would run 4..just thinking out loud.. if i could crank in an inch and really hook up..maybe a checker
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- #299
rick7343
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I assumed the relation fo the rear arms affected weight transfer and traction when on the throttle and brakes. What seems better for forward bite raises the rear roll center which would want to make the car loose in the corner (?). I can change these angles somewhat since I am using a 9" Ford rear and have to install mounts on it anyway...
On stock rear four links and all the 3 links at the track, the upper bar(s) are angled down toward the front of the car with lowers being close to level... Some with stock four links are running with the right rear wheel pulled ahead to combat loose conditions... seems like a bandaid...(?)
Just wondered if there were optimum angles to provide good traction and how it affect rear roll center, or would it change the rear roll center since it is high compared to the front anyway...
So the current thinking is that we want the rear of car to steer out when the body rolls in the turn?
On stock rear four links and all the 3 links at the track, the upper bar(s) are angled down toward the front of the car with lowers being close to level... Some with stock four links are running with the right rear wheel pulled ahead to combat loose conditions... seems like a bandaid...(?)
Just wondered if there were optimum angles to provide good traction and how it affect rear roll center, or would it change the rear roll center since it is high compared to the front anyway...
So the current thinking is that we want the rear of car to steer out when the body rolls in the turn?
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- #300
sierra76
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Having my first go at building a 3 link for dirt track racing.
Wheel base is 101 inches .
Because of tyre rules (Control Tyre) most cars find it difficult to get power down on hard slick tracks
Is there a ideal length of bottom and third links.?
should we run a third link solid or rubber/spring loaded.?
Height and position of 3 link on axle housing?
Angles of links?
Position of coil overs?
I was thinking of running rear mounted panhard mounted RHS of chassis.
Sorry for all the questions but it seems a good idea to start right fiorst time
Thanks
Wheel base is 101 inches .
Because of tyre rules (Control Tyre) most cars find it difficult to get power down on hard slick tracks
Is there a ideal length of bottom and third links.?
should we run a third link solid or rubber/spring loaded.?
Height and position of 3 link on axle housing?
Angles of links?
Position of coil overs?
I was thinking of running rear mounted panhard mounted RHS of chassis.
Sorry for all the questions but it seems a good idea to start right fiorst time
Thanks
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Rick and Sierra, both have questions about rear end set up..
see post # 132 page 9 for 4 link info, post 116 page 8 for rear steer, post 81 page 6 for top link info, post 253 page 16 for 3rd link info and post 261 page 17 for 3rd link spring rate
now about the questions from Rick..we want the angles of the stock 4 link to form an Instant Center (IC) as far forward as possible. this longer lever cushions the acceleration when the tires hook up. Too short an IC distance means we have a lot of angle change on both sides and the car will be real darty when you nail it. Longer is better and gives the driver more control because you don't have a lot of angle change as the shorter IC has. I like your thinking about the rear steer since you are on asphalt and do not have a lot of body roll. You and tune with lower RC but we do not need bandaids..we need a set up to handle the weight transfer and kick enuff weight rearwards on turn exit to hook up. Have you calculated the total weight transfer to the front?
Sierra,,welcome ..please look up the posts and let us discuss your set up once you have looked them over..i am working on post for rear coikl over mounts..but have to make beer run first
RM
see post # 132 page 9 for 4 link info, post 116 page 8 for rear steer, post 81 page 6 for top link info, post 253 page 16 for 3rd link info and post 261 page 17 for 3rd link spring rate
now about the questions from Rick..we want the angles of the stock 4 link to form an Instant Center (IC) as far forward as possible. this longer lever cushions the acceleration when the tires hook up. Too short an IC distance means we have a lot of angle change on both sides and the car will be real darty when you nail it. Longer is better and gives the driver more control because you don't have a lot of angle change as the shorter IC has. I like your thinking about the rear steer since you are on asphalt and do not have a lot of body roll. You and tune with lower RC but we do not need bandaids..we need a set up to handle the weight transfer and kick enuff weight rearwards on turn exit to hook up. Have you calculated the total weight transfer to the front?
Sierra,,welcome ..please look up the posts and let us discuss your set up once you have looked them over..i am working on post for rear coikl over mounts..but have to make beer run first
RM
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- #302
rick7343
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I was reading some info on other sites regarding rear anti squat percentages..
Looks like front anti dive also plays a factor...(?)
Things were so much simpler before I found all these things...lol
Should I post what seems relevant?
Looks like front anti dive also plays a factor...(?)
Things were so much simpler before I found all these things...lol
Should I post what seems relevant?
- #303
smokin butts
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Hey Ranger
Looking at rear instant center height and location ?
where is a good starting point for height and location ie. transmission ,engine or between the front tires.
thanks smokin
Looking at rear instant center height and location ?
where is a good starting point for height and location ie. transmission ,engine or between the front tires.
thanks smokin
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coil over location
Rear coil-overs should be mounted at angle between 13 and 20 degrees. If you can measure the max body roll, mount the shock so they are pushing straight up and down at this point. I did not realize it but coil-overs can effect weight transfer if not mounted properly. I the top of the coil-overs ( this applies to shocks as well) are mounted too high on the chassis they will hinder weight transfer. The top of the coil-overs should be mounted as close as possible or below the Center of Gravity Height. ( Rear CGH ball park 10 to 12 ") Most common is 9 inch stroke shock and what we do not want is to run out of travel. Try to mount the bottom of the coil-overs as low as possible under the axle center line. I think 7 inch is about the lowest you can go before you start to spark the asphalt. Don't forget if you cut a tire you don't want to screw up mounts and chance losing the mount for that race. This bottom mount location helps forward bite during acceleration. When you nail it off the turn, the weight is thrown from front to rear and is resisted by the coil-overs top mount. If you have the top mount higher than the Center of Gravity Height, the weight transfer loads the suspension links and not the coil-overs where it can assist forward bite. Same applies to shocks and coil springs.
Rear coil-overs should be mounted at angle between 13 and 20 degrees. If you can measure the max body roll, mount the shock so they are pushing straight up and down at this point. I did not realize it but coil-overs can effect weight transfer if not mounted properly. I the top of the coil-overs ( this applies to shocks as well) are mounted too high on the chassis they will hinder weight transfer. The top of the coil-overs should be mounted as close as possible or below the Center of Gravity Height. ( Rear CGH ball park 10 to 12 ") Most common is 9 inch stroke shock and what we do not want is to run out of travel. Try to mount the bottom of the coil-overs as low as possible under the axle center line. I think 7 inch is about the lowest you can go before you start to spark the asphalt. Don't forget if you cut a tire you don't want to screw up mounts and chance losing the mount for that race. This bottom mount location helps forward bite during acceleration. When you nail it off the turn, the weight is thrown from front to rear and is resisted by the coil-overs top mount. If you have the top mount higher than the Center of Gravity Height, the weight transfer loads the suspension links and not the coil-overs where it can assist forward bite. Same applies to shocks and coil springs.
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rick7343 said:
Rick..thank you..it has been a long time since this came up,..pls post what you think would help
Smoking...longer is better as long as you don't run into interference from hitting the chassis. We had a super late model , i think it was a port city chassis, has a third link that ran from the top of the quick change to a front mount just behind the transmission.
- #306
rick7343
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http://www.racetec.cc/shope/
Mainly for drag racers, but tons of info and interactive programs...
Tells me how to get the results, if only I knew what results I wanted!
Mainly for drag racers, but tons of info and interactive programs...
Tells me how to get the results, if only I knew what results I wanted!
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sierra76
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Thanks have had a good read on the 3 link posts.
Seems like a sensible approach before we head to a 4 bar
I notice Ranger Mike you like 20 inch bottom arms were as a GRT have approx approx 15 inch arms
What would the difference in length do in terms of handling.
Would the shorter arm allow the LR to climb under the chassis more and more drive but would it also make for incinsistant handling.
On a 3 link should i mount the coil over in front of axle LR and on top on RR.
Any other pointers like angles etc
THanks for the advice
Seems like a sensible approach before we head to a 4 bar
I notice Ranger Mike you like 20 inch bottom arms were as a GRT have approx approx 15 inch arms
What would the difference in length do in terms of handling.
Would the shorter arm allow the LR to climb under the chassis more and more drive but would it also make for incinsistant handling.
On a 3 link should i mount the coil over in front of axle LR and on top on RR.
Any other pointers like angles etc
THanks for the advice
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Sierra..
Longer is better because it produces less angle change as one side moves to bump and the other goes into rebound. Shorter is twitchy if you know what I mean. 4 link suspensions use 15 inch lower links. But if the chassis will not permit longer..go with what you can and follow the instant center rule regarding angles.
The coil over mounting was discussed on post # 304..It would help a little with the coil overs mounts in front on the LR and in back on the Rt. rear..Detroit did this in the muscle car era. Not sure it is worth it when you have to crawl under the cat to change springs at the track...keep it simple
per attached ..just for your information
Rear suspension motion rate - MR = A/B
in this case A = 22 inch B = 32 inch
MR = .688Wheel rate = WR
Motion Rate = MR
Spring Rate = SR
WR = (MR)² x SR x (cos)²example if you run 250 # spring and 20 degree angle
WR= (.688)² x 250 x (.94)² or WR = 105 lbs..
Longer is better because it produces less angle change as one side moves to bump and the other goes into rebound. Shorter is twitchy if you know what I mean. 4 link suspensions use 15 inch lower links. But if the chassis will not permit longer..go with what you can and follow the instant center rule regarding angles.
The coil over mounting was discussed on post # 304..It would help a little with the coil overs mounts in front on the LR and in back on the Rt. rear..Detroit did this in the muscle car era. Not sure it is worth it when you have to crawl under the cat to change springs at the track...keep it simple
per attached ..just for your information
Rear suspension motion rate - MR = A/B
in this case A = 22 inch B = 32 inch
MR = .688Wheel rate = WR
Motion Rate = MR
Spring Rate = SR
WR = (MR)² x SR x (cos)²example if you run 250 # spring and 20 degree angle
WR= (.688)² x 250 x (.94)² or WR = 105 lbs..
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Here is info on Street Stock class round track car
3100 pounds, full size 76 Impala front and rear
50% rear weight, 60% left side with 58% cross weight
82.5" LFT rear tire, 85" rt. rear tire
A-Arm and coil spring frt. 64.7 inch track, 1.5 degree camber over 3 inch
Lf ft 900# rt ft 1000# springs
rear has panhard bar 61" track width
Lf rear 200# rt rear 175# spring
Ft RC is about right height but we have not offset it to plant more weight on Rt ft to help steer thru the turn
Performance Trends is software..nice packageif we raise the right top ball joint to 20.9" the RC moves 3.0 to the right but is now 3.3 Inch height
If we lower the left top BJ to 2.8 Height the RC is now 3.3 inch to the right and 2.8 inch height and we improve chamber ( less gain)
3100 pounds, full size 76 Impala front and rear
50% rear weight, 60% left side with 58% cross weight
82.5" LFT rear tire, 85" rt. rear tire
A-Arm and coil spring frt. 64.7 inch track, 1.5 degree camber over 3 inch
Lf ft 900# rt ft 1000# springs
rear has panhard bar 61" track width
Lf rear 200# rt rear 175# spring
Ft RC is about right height but we have not offset it to plant more weight on Rt ft to help steer thru the turn
Performance Trends is software..nice packageif we raise the right top ball joint to 20.9" the RC moves 3.0 to the right but is now 3.3 Inch height
If we lower the left top BJ to 2.8 Height the RC is now 3.3 inch to the right and 2.8 inch height and we improve chamber ( less gain)
Attachments
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- #310
rick7343
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I was just playing with the same software...lol
Seems Iwill have to raise the upper ball joints and inner moumts to get what I want... (Or what I think I want...lol)
How do you feel about upper control arm angles? Better to keep the shafts perpendicular to the centerline of the chassis or match their angle to the pivot angles of the lowers?
Seems Iwill have to raise the upper ball joints and inner moumts to get what I want... (Or what I think I want...lol)
How do you feel about upper control arm angles? Better to keep the shafts perpendicular to the centerline of the chassis or match their angle to the pivot angles of the lowers?
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Rick
When you have parallel upper and lower A-arms you have an Instant Center way out there in space and very little camber build ( gain). Most round track cars are happy with 1.5 degree camber gain per inch travel since the front end lay out won't permit anything less. When you have a lot of upper link angle you have a radical camber build which could work depending upon all other factors. It is all about tire contact patch..
When you have parallel upper and lower A-arms you have an Instant Center way out there in space and very little camber build ( gain). Most round track cars are happy with 1.5 degree camber gain per inch travel since the front end lay out won't permit anything less. When you have a lot of upper link angle you have a radical camber build which could work depending upon all other factors. It is all about tire contact patch..
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if you can do it, try to make the upper and lower links / control arms/ A-arms equal length and parallel. The hot set up is the camber gain we have here..a little over 1.7 degree for 3 inch travel. Make sure you have zeroed out any bump steer and add as much ACKERMAN as possible. If you can do this on your door flapper racing on Saturday night you can run the outside groove and and lap the field pretty much at will. Its all about tires!
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- #313
rick7343
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I better go back to school and learn how to communicate...lol
I meant from a top view... lower arm pivots are angled ahead (front pivot point closer to the chassis center than the rear) but the upper arm pivots are almost perpendicular to the frame centerline... Is this to change caster as the front dives?
What about antidive?
I meant from a top view... lower arm pivots are angled ahead (front pivot point closer to the chassis center than the rear) but the upper arm pivots are almost perpendicular to the frame centerline... Is this to change caster as the front dives?
What about antidive?
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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. t 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 can not 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).
Leaning wishbones back to arrive at a antidive characteristics was common in formula 1 a while back. Indy cars several teams experimented with hydraulic devices to keep the attitude (rake) of the car constant to get a stable aero platform (was something of a antidive /anti squat system).
With modern (shock) damping technologies you should be able to get on top of most of these problems and not get lost with introducing new variables to combat short comings of your particular car. Why would you introduce a setup that will run out of travel and go into spring/coil bind or use pump stops to handle any weight transfer.
Anti-dive is a suspension parameter that affects the amount of suspension deflection when the brakes are applied. When a car is decelerating due to braking there is a load transfer off the rear wheels and onto the front wheels proportional to the center of gravity height, the deceleration rate and inversely proportional to the wheelbase. If there is no anti-dive present, the vehicle suspension will deflect purely as a function of the wheel rate. This means only the spring rate is controlling this motion. As anti-dive is added, a portion of the load transfer is resisted by the suspension arms. The spring and the suspension arms are sharing the load in some proportion. If a point is reached called 100-percent anti-dive, all of the load transfer is resisted by the suspension arms and none is carried through the springs. When this happens there is no suspension deflection due to braking and no visible brake dive. There is still load transfer onto the wheels, but the chassis does not pitch nose down.
The method to achieve anti-dive is controlled by the upper and lower control-arm pivot points on the chassis. In all suspensions there is a factor called the side view swing arm. This is a theoretical point of intersection of the arm planes projected into the fore-aft vertical plane through the wheel center. If this point is behind the wheel and above the ground, it will produce anti-dive. It will also provide anti-dive if it is below ground and ahead of the wheel. The other possible locations for this instant center are ahead and above ground as well as behind and below the ground. With these locations we have pro-dive. This means as the brakes are applied the suspension travels more than it would without any anti- features. The magnitude of the anti-feature, either pro or anti, is a function of how far the instant center is away from the ground. If it is on the ground, there is zero-percent anti-feature.
On passenger cars, anti-dive is added to make the pitch motions under braking more tolerable for the occupants because of the typical soft spring rates. The anti-dive is made the same for both sides of the car because most people brake in a straight line, and there is no directional preference on the street or in road racing for that matter. In circle-track racing it is common for racers to take any parameter to and beyond its limit. In the evolution of the circle-track chassis, they have come to a solution that provides pro-dive on the left-front and anti-dive on the right-front suspension. The reasons for this are varied. For one thing, as the brakes are applied the car will deflect more on the left front than on the right. This will give a feeling of the front leading into the corner and not rolling out right away. This combination also provides for more of the load transfer to the front to be carried by the right-front wheel than the left front. The total transfer is the same; just the distribution is affected by the anti-feature in the geometry. More load transfer to the left front on corner entry is like taking wedge out of the car with the brakes. Why? When we turn left with a positive caster, the lft ft tire rises and is the result of jacking weight into that corner and taking wedge out of the car. The more positive caster used on the lft ft, the greater the steering axis angle change, the greater the loss of cross weight as we turn left.
Anti-dive has an effect when there is a torque trying to rotate the spindle relative to the chassis. The typical case for this is under braking, but there is another case that can alter the loads and deflections of the wheels. This is the drag component of cornering load. When the wheels are turned and the tires are cornering hard there is a longitudinal load relative to the chassis centerline trying to rotate the spindle. To visualize this, think of the wheel turned 90 degrees!
Just like anti-dive in the front suspension, there can be anti-lift in the rear suspension that reduces rebound travel under braking. There is also anti-squat in the rear suspension under acceleration for rear-wheel-drive cars.
next up Caster...and effect on handling..need beer run
Leaning wishbones back to arrive at a antidive characteristics was common in formula 1 a while back. Indy cars several teams experimented with hydraulic devices to keep the attitude (rake) of the car constant to get a stable aero platform (was something of a antidive /anti squat system).
With modern (shock) damping technologies you should be able to get on top of most of these problems and not get lost with introducing new variables to combat short comings of your particular car. Why would you introduce a setup that will run out of travel and go into spring/coil bind or use pump stops to handle any weight transfer.
Anti-dive is a suspension parameter that affects the amount of suspension deflection when the brakes are applied. When a car is decelerating due to braking there is a load transfer off the rear wheels and onto the front wheels proportional to the center of gravity height, the deceleration rate and inversely proportional to the wheelbase. If there is no anti-dive present, the vehicle suspension will deflect purely as a function of the wheel rate. This means only the spring rate is controlling this motion. As anti-dive is added, a portion of the load transfer is resisted by the suspension arms. The spring and the suspension arms are sharing the load in some proportion. If a point is reached called 100-percent anti-dive, all of the load transfer is resisted by the suspension arms and none is carried through the springs. When this happens there is no suspension deflection due to braking and no visible brake dive. There is still load transfer onto the wheels, but the chassis does not pitch nose down.
The method to achieve anti-dive is controlled by the upper and lower control-arm pivot points on the chassis. In all suspensions there is a factor called the side view swing arm. This is a theoretical point of intersection of the arm planes projected into the fore-aft vertical plane through the wheel center. If this point is behind the wheel and above the ground, it will produce anti-dive. It will also provide anti-dive if it is below ground and ahead of the wheel. The other possible locations for this instant center are ahead and above ground as well as behind and below the ground. With these locations we have pro-dive. This means as the brakes are applied the suspension travels more than it would without any anti- features. The magnitude of the anti-feature, either pro or anti, is a function of how far the instant center is away from the ground. If it is on the ground, there is zero-percent anti-feature.
On passenger cars, anti-dive is added to make the pitch motions under braking more tolerable for the occupants because of the typical soft spring rates. The anti-dive is made the same for both sides of the car because most people brake in a straight line, and there is no directional preference on the street or in road racing for that matter. In circle-track racing it is common for racers to take any parameter to and beyond its limit. In the evolution of the circle-track chassis, they have come to a solution that provides pro-dive on the left-front and anti-dive on the right-front suspension. The reasons for this are varied. For one thing, as the brakes are applied the car will deflect more on the left front than on the right. This will give a feeling of the front leading into the corner and not rolling out right away. This combination also provides for more of the load transfer to the front to be carried by the right-front wheel than the left front. The total transfer is the same; just the distribution is affected by the anti-feature in the geometry. More load transfer to the left front on corner entry is like taking wedge out of the car with the brakes. Why? When we turn left with a positive caster, the lft ft tire rises and is the result of jacking weight into that corner and taking wedge out of the car. The more positive caster used on the lft ft, the greater the steering axis angle change, the greater the loss of cross weight as we turn left.
Anti-dive has an effect when there is a torque trying to rotate the spindle relative to the chassis. The typical case for this is under braking, but there is another case that can alter the loads and deflections of the wheels. This is the drag component of cornering load. When the wheels are turned and the tires are cornering hard there is a longitudinal load relative to the chassis centerline trying to rotate the spindle. To visualize this, think of the wheel turned 90 degrees!
Just like anti-dive in the front suspension, there can be anti-lift in the rear suspension that reduces rebound travel under braking. There is also anti-squat in the rear suspension under acceleration for rear-wheel-drive cars.
next up Caster...and effect on handling..need beer run
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- #315
flashpuppy
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Ranger Mike said:
Yessir. Winter's is whipping together a nice little LSD unit for me.
I am having a bit of diffuculty figuring out a functional rear suspension due to my extremely short wheelbase. If my math figures out correctly, my four-link bars (if I was running them) would need to be mounted about in my abdominal region. I know I'm running into all sorts of problems because of the low ride height/tall tire combination and extremely light weight. I was thinking that a torque link setup would be nice as I could run the third link into the trans tunnel and give myself the type of length needed.
I am looking forward to seeing what you have to say about rear-end mounting.
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