in past days i did some test drives with different rear camber setting, which is quite easy using smart struts
i suggest to persons using the smart struts to experiment this , but not because of camber variations : for rear toe variations

it seems to me that increasing rear camber , rear toe-in is increased too. so it's easier with smart struts instead than moving shims at trailing arms.

It's astonishing how little rear toe-in can affect oversteer.

my rear ride height is already setted so the 1/2 shaft are angled down (per VIP ).
i run a basic 3/8" rear toe-in which is just barely "enough"

i experimented with 1,2 deg neg rear camber and the oversteer was not scary but not negligible

then i moved to 1,8 deg neg ( and related increase of rear toe-in) and now the oversteer seems disapperead.

i have to recheck the rear toe but i suppose is slightly more than 3/8"

so my suggestion is : if your car is tail happy , apply a good amount of toe-in by using smart struts as test,if it works then readjust using trailing arms shims if necessary

 

That seems like a lot of toe and camber. If I'm not mistaken, Chevy calls for something like -7/8 degree camber, and 1/8" total rear toe in.
How are your tires wearing?

 

My car is not a DD . I drive it , fast ,for just 30-40 miles each ride when i have time. so tire's wear is not an issue. btw , after about 500 miles i still don't see uneven tire wear

of course my thoughts about camber and toe-in are intended for aggressive driving and lot of turns (i'm italian , no hiways here, just winding roads)

p.s. I use expensive Avon tires, but BFG are cheap : not a problem to replace rear tires more often , I think, if performances ( and safety) are the target

 

How do you explain this? Have you measure actual toe-in before and after?

 

At the shop we set the "Bump Steer" on highly adjustable suspensions like this Lola to "Zero thousands of an inch" for the full vertical travel of the wheel.

The racing Vettes or even mine. We disconnect the rear spring and then shim the trailing arm and change the inner radius rod mounting position and length to get "bump Steer as low as possible for the whole vertical travel of the rear wheel







I tore up the half shaft. So this is picture of getting it ready to set rear toe and bump steer Pic from 2002

 

Hello,

Maybe I can ask a couple of questions and relay what I have found.

When you say "oversteer", is that on corner entry, through the middle of the corner with "maintenance" throttle, or power on oversteer out of the corner - If I know anything about C3's is that you are probably referring to power on oversteer out of the corner. C3's are not tolerant of "trail braking" into a corner, it is a guaranteed oversteer no matter how you have the suspension set. The rear just jacks too much under braking and the front, consequently, has too much grip. The only solution for this is a C4 or guldstrand setup.

When you say that the halfshafts are pointing down, I understand what you mean, but I think the better way of looking at it is to set the vertical distance from the inner camber arm pivot to the outer camber arm pivot at the 1.00" to 1.25" suggested by the chevy power guide. This minimizes toe changes as the rear suspension moves. I think if the half shafts point down, you have roughly lowered the car to these values. (The smart struts have an adjustment on the inner camber bolt position, so this may not be the case. )

I can say from my experience is that "toe" settings are not the only cause of oversteer. It is the camber setting that seems to be the key. Note changing the static camber setting should not change your toe setting unless you have moved the inner camber rod attachment point to get the camber increase - you just used the adjustable rod ends - right? If so, the toe did not change when you reset the static camber.

What I have found seems to be that the relationship of the front to rear camber settings is the primary influence. My car will oversteer if the front has to much camber than compared to the rear. When the front has too much camber, it has more lateral grip, then when the power goes on, the front bites and the rear swings out. I had power on oversteer (snap response) for a long time and I thought, well I will reduce the rear camber to try to get the tire flat to the ground on acceleration. Wrong direction, made it worse. I added negative rear camber and the car began oversteering less and less. Now, the car is much more neutral, back all the way off and the car understeers a little, full throttle and a much gentler oversteer (drift). My camber settings are - 2.0/2.5 front, and -2.0 rear. When the car was set with -1.0 rear and less, the snap oversteer begins to happen. really scary on a wet track.

Setting the toe on a C3 can be very confusing also. 3/8" sounds like a lot, but it depends where the 3/8" was measured. If you have too much toe in, the tire is already running at a static slip angle - if 3/8" is measured at the front of the tire, this is about 2 degrees of static slip angle. When cornering, considering the outside tire, the turn slip angle adds to the static slip angle. With modern tires, they can only handle a small slip angle as compared to the old Bias tires (about 3-7 degrees for modern radials, 8-16 degrees for old Bias tires). Anything over 3-7 degrees of slip and there is no more lateral friction increase, and eventually a decrease in friction. So, I think too much toe-in causes a loss of cornering grip. I also found this out on a wet track. I had too much toe-in and the car was intolerant of any throttle increase exiting a corner.

Did this make any sense?

 

please explain to us all how exactly you "set" bump steer on the rear of your Corvette.....

 

You know without a 4 or 6 link it is more like limiting bump S. You change the toe and adjust the under the differrential Smart strut vertical mount point. You also adjust the static rear ride height and use enoungh spring to minimize change during the vertical travel of the wheel.

Please tell me how you minimized camber and toe changes on your race car?

We have used the adjustable trailing arm frame mount point bolt assembly to aid in quicker rear toe changes. The central cam adjust mount point of the radius rods really help also.

 

thanks for the interesting read.
no power oversteer out of the corner . I felt oversteer entering the corner at steady speed. I thought about a rear toe change because i felt the oversteer even if taking the turn not that fast , so i excluded a tire grip issue (camber affected). 245/60/15 Avon race tires
But your tests with different camber settings are enlightning.
my car is setted now with 1,5 deg front and 1,8deg rear neg camber.
i experimented also with little rear toe-in ( close to zero) and dangerously oversteered.so i went back to about 3/8" ( measured as difference between front and rear of tires )
Now the car is just fine .I tested a similar camber and toe setting at the racetrack too : actually i had 1,8 deg at left rear and 2,4 deg at right rear - the mismatch was not intentional but i left it anyway because i was curious to feel any dfference in left and right hand turns : not big difference indeed , my car just likes a lot or rear negative camber.

I think i will take the front camber to 1,8-2 deg neg and see what happens

at the racetrack i didn't had a tire pyrometer unfortunately....but sincerely i rely more on my driving sensations.

the last test i want to do is to have somebody taking a photo from front while hard cornering ( there's a new road close to my house where i can easily do it ) and see how tires look in respect to the ground. I've seen some photos like this and i believe that it's possible to learn a lot from them

 

Well, think about it for a moment. When you adjust the rear camber on a C2 or C3, you are moving the bottom of the wheel/tire in or out. This changes the wheel track, the center to center distance between the contact patches of the tires on the same axle.
For example, increasing negative camber increases the wheel track. Since the trailing arm's pivot point in the front hasn't moved, you would increase the rear toe in at the same time..

 

That's my idea too.
The point is that the toe measure is done at the same heigth of wheels center ( hub) so it will reveal no toe change when changing camber... but actually the toe change happens.Or am I wrong?
This would explain the dramatic handling change when adding negative camber: it's a geometrical change in the suspension , not a matter of more or less rubber on the ground ( camber) because oversteer effect is felt also at low speed