I keep hearing suggestions for negative camber for autocrossing, but that seems backwards to me. Negative camber means the top of the wheel leans inboard right? Wouldn't it be better to have a slightly positive camber setup so that it turns into neutral camber, or barely negative in a corner? This way would compromise some straightline traction, but maximize grip in a corner. This is how I understand typical suspension geometry works when compressed, so please correct me if Corvette geometry is different and introduces positive camber with compression.

Eugene

 

Actually, you've got it backwards. When the suspension compresses, it induces positive camber, leaning the top of the tire outwards. This is true of all double wish bone, or control arm, suspensions. Race cars are generally set up with a fair amount of negative camber to compensate for this and get the tire as flat as possible while cornering.

 

Suspension compression gives you more negative camber, not the other way around. I am fairly certain, could someone confirm that?

On hard cornering, you don't want the wheel to be vertical. The tire is pulled to the side and deformed on cornering, and negative camber helps keeping a good tire contact patch without destroying the outer edges of the tires.

Till

 

You definitely want a slight negative camber.

When you go into a turn the balance of the car will put extra weight on the outside front wheel. For control and steering, you want as much tire / road contact as possible on that wheel.

The force of the turn will tend to shift / flex / deform the loaded tire inward. With negative camber this will put the loaded tire almost flat on the road.

If you had positive camber, the inside of the loaded tire would be off the ground.

Any questions on which camber to use, just turn on the speed channel and watch any race. All the cars have negative camber.

Note: This is my morning pre-cup of coffee explanation.

 

Check out the Autocrossing and Roadracing section. There is lots of info there.

 

I usually only see alignment recommendations there, but not explanations on how the geometry was affected. I've learned quite a bit from this thread, but I believe there's still more to learn....

So the positive camber is setup during alignment because even though the geometry of the control arms are designed to maintain perfect camber during compression, the control arms bushing deform and introduce negative camber. To offset the move towards negative camber caused by the bushings ideally results in zero camber in a corner. Does that sound about right?

If I'm on the right track, then stiffer control arm bushings, particularly in the lower control arms, would permit the camber settings to be set closer to 0 degrees. So far the only aftermarket control arm bushings I know of for sure are polyurethane bushings. I've heard a little talk about LGM metal spherical bushings, and nothing of delrin/aluminum.


Eugene

 

Looks like we have two opinions, suspension compression produces neg. camber and suspension produces pos. camber, and where did you get that defromed bushings generate neg. camber? I didn't see where anyone said anything about that.
Anyway, generally speaking, production cars generate more positive camber as the suspension is compressed. High performance race cars, such as the NASCAR hand crafted frames do just the opposite. They generate more negative camber as the suspension compresses. It just depends on where the components are attached to the frame in relation to the center lines of the ball joints on the spindles.
Best autocross performance requires neg. camber on all wheels for right and left turns. Best oval track performance requires neg. camber on front and back right side and pos. camber front and back on left side like NASCAR runs for left turns only.

 

Johnny S, I'm not sure I agree, at least when looking at a picture of the rear suspension.



Those upper control arms look to be shorter than the lower control arms, with the lower control arm being mounted further inboard, and they both appear to be parallel to the ground. This would cause negative camber during compression since the longer lower control arms will require more vertical movement than the upper control arms to move as far horizontally, so essentially the upper control arms will be pulling the top of the wheel towards the middle of the car.


-- StockCarRacing.com

In any suspension with upper and lower control arms, the lower control arm is going to take most of the weight transfer. This would explain why the GM T1 kit includes an upgraded front lower control arm, but leaves the upper control arm alone. Anyway, when compression occurs in a corner with zero body roll, the control arm bushings, being rubber, will deform, and the control arm bushings closer to the ground and on the outside of the corner, will take the brunt of the force and deform the most, thus increasing camber.


I had it backwards, sorry if I confused anyone. I meant...
Except the rear suspension doesn't maintain perfect camber, it creates negative camber during compression with no body roll.

The bushings might possibly be able to absorb a tenth or two of negative camber, which I would see as a good thing...at least until body roll is considered. Body roll would introduce positive camber. Here's a table to simplify the details.

Rubber lower control arm bushings=Positive camber
Polyurethane lower control arm bushings=Positive camber, but less than rubber
Delrin lower control arm bushings=Positive camber, but less than polyurethane
Compression without body roll=Negative camber
Body roll=Positive camber

It looks like compression and body roll are setup to combat each other, hmm... This makes picking suspension components upgrades tricky. About the only thing I'm pretty firm on is using stiffer bushings to reduce toe-in/out changes. Is this frustrating or confusing anyone else other than me??

 

The negative camber gain in the front and rear suspensions do neet keep up with the positive camber induced by body roll - body rolls 3 degrees, suspension gains 2 degrees of negative camber as it compresses, you are left with 1 degree of positive camber at the tire/road interface. This is what the static camber settings try to overcome, so that you net out to 0 or slightly negative when the suspension is rolled and compressed.

The front suspension gains camber better than the rear, the loaded rear almost always goes positive, as you can only set a limited amount of static negative camber into it.