romandian

please enlighten me on (the new to me) corvette 2000 suspension geometry.

camber. if car is jacked up i have 0.65° front camber and 0.90° rear camber (thats already weird). when measured as driven into garage front is 0.5° and rear is 0.5°. so does this thing loose camber in the corners? (very weird.)

the car is very unstable under hard braking. i found out why. it has toe-out in front. can anybody explain this? so far i thought, toe in is needed in front to make car track properly, when wheels get pulled back. so far increasing toe-in on all my cars has improved braking stability. why the toe-out?

also the rear seems to have toe-in. again this is weird. as you apply power, toe-in gets larger and car reacts to bumps. i have read (on here), that larger toe-in inceases stearing in response. how can that be? when steering in you want the car to oversteer. it should have toe-out in the rear.

does anyone have reliable data on the camber and toe changes during bump and rebound?

does anywone have the castor formula?

thanks.

Solofast

You NEVER NEVER NEVER want toe out in the rear. That will cause roll oversteer and will make the car unstable and handle terribly.

If you are tracking or autocrossing the car you may want a bit of toe out in the front at the event, but driving a car with toe out in the front on the street will keep you awake. It will "nibble" and "tramline" over bumps and can be unstable when going straight, depending on the tires you have. Tires with softer sidewalls will make the car more unstable than stiffer sidewalls.. Toe out in the front will also eat your front tires faster than anything else you can do with your alignment.

Properly set up (correct ride height) these cars will have some camber gain as the car rolls, but it does not totally compensate for the roll effect. For that reason folks serious about getting the best handling put negative camber in the car all around to increase grip. The factory spec for the base suspension does not have as much negative camber as the Z06 spec, and serious folks will run as much as - 2 degrees of camber in the front and -1.5 in the back. That does tend to wear the insides of the tires but that's the price of optimum handling.

Lastly these cars can lose alignment when the adjusters slip. This is a common occurrence. Most racers mark their alignment eccentrics with a stripe of paint or nail polish and that way they can tell if the adjusters have slipped (and they don't have to go back to the alignment shop to put it right if it does slip). If your car is lowered excessively that can cause the adjusters to slip when the car bottoms out. What happens in this case is that the bottoming of the shock puts a "wedging" force on the lower control arm and this pulls the adjuster out of position. You want to make sure the adjusters are tight and are marked so you can tell if they slip.

argonaut

It's very common for a C5 to be unstable under braking, the rear end will dance around noticeably in a brake zone. This can be tamed in a number of ways. I know one guy who put a 8 inch spoiler on the tail and said totally tamed the wiggle. But what worked for me was a switch to some good coilovers (LG G2 Bilstiens). Made a huge difference. The car also has an agressive track focused alignment.

Two weeks ago at VIR I was following my buddy around nose to tail. His car is a C5 Z06 with stock suspension - not sure about his alignment. Following him into turn 1 and turn 11 I was amazed at how much his car wiggled...while the rear end of my car was firmly planted.

Nowanker

Working from memory... stock suspension increases toe in with compression (bump) F and R. Baer and probably others sell bump steer kits to eliminate it, works on either end of the car.

yakisoba

toe out in front can help you turn in, but can dart a bit under hard brakes. Toe in in the rear can help if your springs are really soft, as the car gains toe out under hard acceleration as the suspension squats. On coilovers and the right springs, you don't have to worry as much about the rear, or the front for that matter. Also, poly bushings or sphericals really help these cars. In fact, I don't know if you need much more than the stock camber maximums if you are able to put sphericals in. On stock bushings, which deform quite a lot, you need all you can cheat out of the thing.

63Corvette

I agree with this! Note a good place to start with your suspension alignment specs is the Pfadt alignment specs still listed on this Forum

romandian

pfadt specifies 1/16" toe in in front and back for street and 1/16, 1/8 for performance.

well, i found another sheet, where toe is always zero. while camber goes up to -2.5/-1.9 for track, the recommended caster is 3-6° in that case. why would that be?

Solofast

As the front wheels steer, because of the kingpin angle you lose negative camber. That is, higher steering angles lose more camber than lower steering angles. For that reason in lower speed events, like autocross, you want more caster because you are pulling high g's at high steering angles (lower speed). At higher speed you aren't running at high steering angles, so high caster is less important.

Zero toe is a street setting, or a compromise for someone who doesn't want to mess with toe settings at the track. If you want turn in on the track or in autocross you use toe out in the front. But since toe out eats street tires like crazy some folks will run zero toe as a compromise.

You always want some toe-in in the rear since that provides stability (roll understeer) and also prevents the rear from stepping out under power.

romandian

"You always want some toe-in in the rear since that provides stability (roll understeer) and also prevents the rear from stepping out under power"

this i understand.

"If you want turn in on the track or in autocross you use toe out in the front."

that i dont. will toe out not make car understeer?

"As the front wheels steer, because of the kingpin angle you lose negative camber"

this is a mystery. isnt kingpin angle castor? how can you loose camber with 7-8° castor. or what makes you loose camber when turning in?

Sportsman2003

Hey, can you supply a link? I have been searching and haven't been able to find the setup sheet. I am having my Z aligned dec 1st.

383

http://www.pfadtracing.com/blog/wp-c...-9.12.2011.pdf

Solofast

King pin angle is the angle of the spindle axis when viewed from the front of the car. Caster axis is the same axis as viewed from the side.. Cars like our Corvette, in order to get zero scrub radius have a larger kingpin angle. As the spindle rotates, this results in more positive camber on the outside tire the more you turn the steering wheel. Increasing caster does the opposite and counteracts the effects of the kingpin angle. Remember that the wheel bearing axis is horizontal in the straight ahead position (or slightly cambered for a performance application) but it shifts as a result of the kingpin and caster angles. As the car steers the bottom line is that you get changes in camber as a result of those angles.

While the effect of roll onto a toe'd out front tire is to increase understeer, the initial turn in happens when both front tires are nearly equally loaded, and that's where toe out works its magic. Once the outside tire is heavily loaded there isn't any load on the inside tire so what you have for toe at that point is moot.

romandian

thanks for explaining kingpin. will have op think about it.

but: "that's where toe out works its magic" i still dont get. if you want better turn in and both tires are loaded equally, how does toe out help?

Solofast

Plenty of theories, but one that seems to me to be most credible is that toe out increases transient understeer. Now you would think that increasing transient understeer would make the car turn in slower, but it was explained to me this way by a vehicle dynamics expert...

A car that has more oversteer has to develop yaw angle before it can generate lateral G force. That is in order to develop any lateral force you have to get the car to rotate first. This takes time. A car that has transient understeer will develop lateral G's as soon as the front wheels are turned. For that reason increasing transient understeer allows the car to generate lateral g's immediately and that is what initial turn it is all about.

There are other theories that I've seen but none seem to make as much sense as this, but stiffening the front shocks has the same effect, it makes for transient understeer, but the car responds faster.

383

Great explanation