Race car suspension Class

missile07

I am afraid that the amount of rear steer caused by the left rear going forward is breaking the tires loose when picking up the throttle.

Also we run a limiting chain on the left rear to keep the rearend from dropping so far...could this be pulling the left rear off the ground? it seems like playing with the car on the jack stands that when you jack up on the left side frame and the left rear tire begins to come forward, the weight moves to the right side and the left begins to come off the ground. in race conditions (dry slick) this would seem like there is no weight left on the left rear with all the steer and weight transfer to drive off of the left rear.

Sorry if that was confusing. If you get a chance look at our cars on www.cherrymotorsports.net and how they are responding in photos. This may help

Ranger Mike

this is just my opinion but i think you turned the suspension into a three legged milk stool when you chain stop a corner...this makes a big go cart out of a flexy 4 link suspension..a few of the photos look like the car is NOT transferring equal load to the front tires. tell me about the front set up..what are the spring rates? you using metric a-arms or straight axle?? front sway bar??

to me if the tires spin coming out of the corner you have to adjust the torque link to cushion the shock of matting the gas pedal...thats what its for..
unless the car came with the chain tie..it is a bandaid and i think we have to look at the front springs to make the 4 link work the way it was designed to..

missile07

The chain is part of the chassis builders recommendations. Without the chain the left rear would continue to drop to the point of the shock topping out. We have ran without a chain before and pulled the shaft out of the shock body.

both of our cars are GRT chassis and run the same setup. Chevelle front end with 600 lb springs on both sides as suggested by GRT. we run a stock lower a-arm with a tubular uppers that have been moved from the orignal stock location by GRT. they are adjustable for caster & camber.

I think the general idea of the LR chain is to allow the left rear bars to gain angle and rear steer but stop it from going to far. I was told once before to think of the chassis as a seesaw. If the right front goes down then the left rear comes up and opposite. So i would think instead of going to a lower right front spring we would want a heavier spring to add weight to the left rear?

Ranger Mike

I am with you on stiffer right front spring.
I would stick a 750 lb. spring in right front... i like making one huge change until the car dramatically changes then backing off until you get what you want.

from my set up notes 750 rt ft..700 left ft
200 rt rear, 225 lft rear. 2300 lb car


Is there any way to get some good tire pyrometer readings on a dry track?
alternative is tire wear gage,,.

we need to get all four tires working to carry as much equal load as possible. ..

missile07

I can get tire readings this weekend. Both rear tires were hot and glazed over after the last feature race. I think they were just sliding and spinning.

mender

Then you either need a shock with more travel or you need to limit the travel via spring rate changes. Using a chain won't cure the problem, just keeps the shock in one piece.

As soon as any part of the suspension binds or locks or hits the end of a stop, the spring rate on the wheel effectively goes sky-high and that tire loses traction. If it is a solid axle like yours, it also changes the spring rate on the other wheel the same way, again causing a loss of traction.

By using a chain or a short shock on the left rear, you're making the right rear act like it has a soft spring when that car is flat and a hard spring when it hits the stop as it roll. This can change the handling rather abruptly with only a small change in roll angle and make the car a handful.

Get the chassis movement/roll under control like Mike is suggesting.

missile07

I wish I could attach a photo of the suspension on here for you to see.

The shock on the left rear does not currently top out. When the left rear drops it will continue to drop until something binds, whether that be the shock or the driveline(driveshaft into transmission). The chain is mounted from the top frame rail to the top of the axle tubing. When the rearend drops to 18 inches below the top frame rail the chain grabs.

I agree that this going solid effect would mess with wheel weights. What some people have done is make a rubber bushing limiter that when the chain is about to go tight it begin pulling on the rubber bushing. I guess this is sort of a cushion.

Again I understand the logic behind removing the chain but we have done this before and have ruined several shocks & bent drive shafts.

You talk about limiting travel with spring rate changes....how would I do that? Heavier RR springs?

Ranger Mike

i think that the 600 lbs springs are bottoming too much, upping the frt spring rate should help control the weight transfer to the point you will not run into chain bind. Right now, the weight is coming off the left rear and hammering the right front tire to the point it is skidding..not sticking.. stiffer rt frt spring will compress and then rebound and throw some of the weight back on the left rear where it can help drive out of the turn. right now , like you said,,you got a tetter totter going on..its lifting of the lft rear and sticking and staying up front,,
make sense??

missile07

I agree that maybe too much weight is staying on the RF instead of transferring back to the rear but the LR is always going to hit the chain, top out the shock, or bottom out the drive shaft through the motion of the 4 link suspension.

missile07

Here is an example of the chain and suspension I am talking about. This is not my car but one very similar. The chain is red and you can see it between the spring and front shock.

Attached Thumbnails

 

HowlerMonkey

There is no single process that works with all race car suspension.

The car's class determines ultimate suspension development.

An evil "anti-chapman" once said......"any suspension will work...if you don't let it" so it really depends on your very specific application and rules more than suspension theory.


That said, this thread is full of great discussion and advice for a variety of very different applications.

Ranger Mike

Thanks Howler,,glad to see another wry cynical racer has joined the fray..

I got a PM..from a racer who wishes to remain anonymous..

He drives his own dirt late model car. He is finding that the farther the roll center moves right during cornering while still staying above ground the better his car performs. He asks for input regarding this...

Secondly he finds that the left wheel camber going negative while turning left does not effect performance. How far right can the roll center move before it stops helping performance?

Ranger Mike

I got a PM..from a racer who wishes to remain anonymous..

He drives his own dirt late model car. He is finding that the farther the roll center moves right during cornering while still staying above ground the better his car performs. He asks for input regarding this...


OK... if you read post 5 and 6 above it is a good review of RC height, location and Weight Jacking..
On dirt we use a very hard tire compound which requires a lower roll center to create more down force and bite. Lower Rc means more body roll and thus more side bite.

On dirt the RC is located to the Right side of the cars center line. See the diagram of weight jacking in post 6 above.

Secondly he finds that the left wheel camber going negative while turning left does not effect performance.
It may not if you are lifting the left front...need more info on this point,,

How far right can the roll center move before it stops helping performance.....
We locate the RC to the right by 3 inches to create enough leverage ( using body roll) to plant the right front tire so it sticks on corner entry. This lets the rt front tire steer and turn properly going into and at mid turn. IF we place the RC too far to the right we have too long a lever... thus lifting the left front tire as the body rolls. This will load the rt. rear tire too much under acceleration.
If we locate the RC to the LEFT of center, the car will not turn well..not enuff force to plant the rt. front tire..car will push going in and be loose coming off the turns..

HowlerMonkey

I typed a long post and it disappeared.......am not typing it again as I will be busy downloading data and reducing it from our testing at the space shuttle landing facility runway......maybe later.

I didn't have any counterpoint in that post to what was written by others in this thread.

This forum seems to be governed by logic and scientific method which puts it above most any other forum I have yet seen.

Ranger Mike

Thank you and I hope you will have time to review our efforts from time to time...very glad to have you notice our efforts here..
RM

Fahlin Racing

I haven't read the book you are using here, but I have read Herb Adams', and he states that when Vertical Load gets too high (for whatever design is being used) is not good, in turn reduces cornering efficiency of the vehicle.

Good stuff Mike, albeit, thought I would add that into here to add more to the visualization on VL.

Ranger Mike

thanks Fahlin....good advice..
that is a classic "Push" developed by over loading the tire CF...thats what gets beginners confused when the front end pushes..is it the rear tires hooking up too much or are the front springs too soft????

When i first started " round tracking" I watched all the old timers hot lap and they would always get out of the car and walk around to the right front tire and put their hand on it to see if it was "hotter" than the right rear tire..tire pyrometers were way too expensive back then..they wanted to " make her loose and then tighten her up"...
it was all guess work back then...we had something like 7 cars racing from one small town of 10,000 people..
these were "Hobby Stocks"..big V8 in 1955-1957 Chevy, Fords were popular...we ran a 1964 Ford Fairlane. too much nostalgia..sorry..

racing is a compromise ..the chassis only really works with one set up at one particular time on one particular track for one unique set of tires at one ambient temperature...constant tuning is required to WIN...