Negative Camber Gain, one size fits all?

[68Formula]

Different manufacturers quote values for camber gain with the idea that more is better. Isn't the desired amount dependent on spring rate?

The idea of camber gain as I understand it, is to maintain a flat contact path as the side-loading of the tire increases. If the gain was ideal for a car with 600lb springs, then you replace with 400lb springs, the lean would increase and therefore more camber gain for the same entry speed would result. It seems too much camber gain would over-compensate for the tire loading, therefore reducing the contact patch to the pavement.

Am I off-base here or is there something else going on?

Sorry in advance if this is not technical enough for the forum. I really wanted to get some experienced answers.

[chicane67]

Different manufacturers quote values for camber gain with the idea that more is better. Isn't the desired amount dependent on spring rate?

Yes... and your example explains the theory as best as it could be.

[David Pozzi]

You got it, but add a couple of other variables.
Taller profile tires like a Nextel Cup tire flex a lot more and more neg camber gain is needed to keep them flat compared to a low profile radial tire. so you really need a tire performance curve to design a camber gain rate.

Rather than relate to spring rates, it's probably better to relate to roll rates in degrees per "G" Then figure the car will corner at 1 to 1.2 G's for any sustained period of time if it has DOT race rubber, somewhere around 1G for super high perf street tires.

A low center of gravity car will roll less and can get away with lower spring rates and roll rates and still corner pretty flat. So the opposite is our old muscle cars with higher CG and front weight bias.

The danger of too much camber gain is too high a roll center and front end bobbing on flat or off camber corners due to jacking effects.

Lots of positive caster can substitute for neg camber gain, it tilts the top of the tire in when you turn the wheels.

David

[68sixspeed]

yes, you are on the mark in theory. The amount of body roll also play into it. (which is also affected by the spring rate, roll center, and sway bar) It's sometimes hard to get your mind to picture the dynamics correctly, but remember that the tire/wheel is not moving up and down in the corner unless you hit a bump-- the chassis is doing the change in height and roll. If the gain is off too much then the tire does not maintain contact across it's width.

In actual practice sometimes an even contact patch is not the fastest on the stop watch. A bit more inside tire temp and pressure seems to lap faster over the long run. (i.e. more static camber or a camber curve that increases camber at a higher rate) If the outside edge temps are higher, it may lap fast for a while but it will usually fall off sooner and wear the tires badly. There are downsides to too much camber gain though. (edit- Dave and I were posting/typing at the same time, no sense repeated what he said better!)

[68Formula]

Good stuff! I was thinking I should be talking roll rates, but I was using springs to simplify. Tire deflection due to contruction and stiffness? That should also be high on the list.
Thanks folks. If you have anything else please let me know.

[David Pozzi]

Avon Tire used to have some tire performance charts on their web page, but I see they no longer have them.
Charts like that are not very available from the Manufacturers.
David