Negative wheel travel

[Yorl]

Hi everyone!
I've been given a project to fix (race car), and the first thing I've noticed is the ride is crap...
Having a look at the suspension, front shocks have a total of 6 inches of stroke, but just 2 when the car is with the wheels on the ground. Same thing happens in the rear, 1 out of 3 inches.
I don't know much about suspension, I'm more into engines and engine management but, my idea is, on a race car you want as little neg travel to keep the wheel movement to the minimum, right?? Should I order shorter (as in body length) shocks?? Or am I being paranoid??

 

[patprimmer]

What do you think will happen to the inside wheel as the car rolls in a corner and the shock bottoms out?

Regards
Pat
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[Yorl]

66% front and rear negative travel??

 

[imcjoek]

I've been given a project to fix (race car), and the first thing I've noticed is the ride is crap...

Race car == crap ride. Sounds about right to me.

on a race car you want as little neg travel to keep the wheel movement to the minimum, right??

Artificially limiting wheel travel, negative or positive, is generally bad juju. If you're on the bump stops often, things have gone south. If you're wheel is dangling off the ground, you're obviously not getting any benefit from even having it. Race cars (that can mean many different conflicting things, so you need to be more specific) can tend towards short suspension travel as a means to reach other goals (low CG, etc). It is not the end goal in itself.

 

[Yorl]

By crap ride, I don't mean it's stiff or anything like that. When we get back on power it squats A LOT, the front wheels have an awful lot of travel and we lose control over the front end. Basically the shell is moving WAY too much. It's a 944 track car, 800lbs springs and we got a set of Ohlins coilovers. Problem is, when they ordered the shocks they sent the stock Bilsteins and asked for a copy, but with Ohlins valving. Car runs very low, that's why I think shocks are way too long, OEM length!

 

[Yorl]

If you see the car powering out of a corner, it totally looks like a baja truck...

 

[patprimmer]

Well if it's got plenty of reserve travel it will never lift off the ground, HOWEVER if you limit the travel it may very well come off the ground. Never coming off the ground is never a problem. sometimes coming off the ground is a proble.

% travel means nothing. If it has1/4" travel, then 100 % extra is still SFA.

If it has 25" of travel then 20% is still quite a bit.

Yes, some race cars have 25" of travel and still have wheels come off the ground.

Regards
Pat
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[GregLocock]

I suggest you read around a bit about what suspensions actually do before you touch a thing.

Alternatively throw changes at it, spend money, and continue to lose races. Your call.



Cheers

Greg Locock


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[AeroFC]

Stiffer spring rates in the rear and of you can adjust the dampening front and rear

 

[homologator]

Is anyone still watching this thread?

The suspension travel is related to the spring rate - do the springs rattle at full droop?

An 800lb/in spring is unlikely to defect much between full droop and ride height.

The actual deflection depends on the weight carried by the wheel and the mechanical advantage of the linkage.

The 6" full travel looks like the factory standard amount; the stiffer springs won't move as much.

Your suspension travel is the wrong way around - you will need a small amount between full droop and ride height and the rest above that. this is a very common problem on amateur modified cars.

You need to read as much as you can - carrol smiths "Tune to win" or Fred Puhns "How to Make Your car handle".

Be careful with this car - if there is insufficient travel the driver may loose control over bumps.

 

[140Airpower]

Yori, lots of race cars corner with one wheel off the ground. Look at front wheel drive racing sedans with the inside rear lifting and Formula one cars with the inside front lifting. This can be the result of a hard limiter like the shock stroke or a suspension strap or it can result from roll stiffness. When there is a hard limiter the handling characteristics will usually experience an abrupt change when the limit is reached -not good. But, when lifting is the result of roll stiffness, the driver shouldn't feel it.

Lifting from roll stiffness is a consequence of disproportionate roll stiffness at that end of the car compared to the weight being supported and is always seen at the non-driven end. It should be the front of a rear drive car and the rear of a front drive. Cornering on three wheels is not necessarily bad, but it does indicate that the car setup has reached or is reaching the limit of setup adjustment.