Race Tire Dynamics 101, Help me understand camber for slicks... Options

[nine14cats]

We've had these type of threads a few times...so here is a recap from our collective personal experiences:

Driver Make Fr/RR Camber
------- ------- -----------------
John Rogers Goodyear ~0/0.25
Racer Chris Hoosier ~0.7-0.9
Brad Goodyear ~0/0.25
Roger Kraus Goodyear ~1.0/1.5
Bill Pickering Hoosier ~1.5/2.0

I tire tested this year both Hoosiers and Goodyears doing auto-x's, TT's and open test days. What I found was that with my driving style, the car was faster with a more camber using Hoosier slicks and the Goodyear slicks licked a little less.

Is this due to tire construction? i.e. the sidewall is stiffer in a Goodyear than a Hoosier?

The reason I ask is that I'm looking at different combinations for next year. I like my 15x7 rim / 23x9.5x15 cantilever slick setup for Auto-X. Combined with my 901 that has been re-geared, I have a very competitive setup.

For Track Events I have a few choices. I can run the same tire/wheel combo as auto-x's or I can run Dot-R's any size. However the camber issues switching between the 2 types of tires makes it a pain.

I was talking to Roger Kraus and he also carries Dunlop slicks in 18" sizes and there are Pirelli slicks in 18" sizes as well. I have a spare set of 18" rims that came off of my 911 I just sold, so I could do more tire testing. The taller tires (~25.2" versus 23") would help on the big tracks I believe. What is interesting about the 18" slicks is that they like between 1.5 and 3 degrees of camber.

That's why I'm interested in understanding the dynamics of the camber settings....I've got alot of options and I plan on tire testing this winter to prepare for next season.

Anyone's comments or experience would be appreciated!

Thanks,

Bill

[john rogers]

The construction of the Goodyears is different than the Hoosier slicks and they do require more negative camber. The Goodyears are bias ply tires with stiffer sidewalls than the Hoosiers which I think are radials (could be wrong there?) Additionally if you run larger sizes such as 17 or 18 inch Goodyears they need much more negative camber. As always, the best way to teat then is to do an alignment and then do some runs then chenge the alignment and do some more runs to see what tire temps are doing. But having said that, if you are happy, stay with the setup you have. Good luck.

[MJHanna]

The Goodyears are bias ply tires with stiffer sidewalls than the Hoosiers which I think are radials (could be wrong there?)

Both Goodyear and Hoosier make bias ply and radial “slicks” both use a different set up. If you have set it up for Bias and switch to a radial your car will not handle the same. (IMG:style_emoticons/default/ohmy.gif)

[nine14cats]

Both the Goodyears and Hoosier slicks I'm running are bias plys. Goodyear factory reps say 0.5 camber, Hoosier factory guys say 1 to 1.5.

For Hoosier Radials (RSO3's), the factory says 1.5 to 3.0 degrees camber depending on the weight of the car. More weight, more camber.

Bill

[KenH]

Are you looking for that second Rich beat you by at Marina?????????????

Ken 180

[nine14cats]

You bet!

I'm actually right in the middle of upgrading the car. First and foremost is weight reduction. The car as it sits is probably heavier than stock with all the metal still on it and a full cage in it.

I've got f/g everything ordered and it will be going on the car. (IMG:style_emoticons/default/laugh.gif)

I'm just looking for more knowledge on tire dynamics in this thread as I want to be quicker on the track next year...it's a balancing act in setups and cost... (IMG:style_emoticons/default/barf.gif)

Bill

[Blake]

The "correct" camber only partially depends on the particular tire; mostly it depends on the particulars of the suspension.

Obviously, the tires deform relative to cornering force. Perhaps not as obvious is the fact that the best grip is obtained at zero camber. Because the tires deform, some negative camber is always required to achieve zero camber under cornering force. If you want to read more about this, pick up the latest issue of Driving Sports magazine and read my tech article on the subject. (IMG:style_emoticons/default/smile.gif)

However, the main factor in determining what camber is right for any particular car is most dependant on the car setup. This is because the geometry of the suspension changes throughout its range, cars roll, pitch and yaw, and suspension components and bushings deflect under load. Okay, let's start with deflection....do you have rubber, nylon (or whatever plasticky alternative), or metallic bushings? Cornering forces will cause rubber and plastic bushings to deflect in the favor of positive camber, obviously affecting rubber bushings more. Metallic bushings (or rod ends) will not deflect. Are all the suspension somponents stiff enough? If not, they too will deflect and change suspension geometry. What about the roll stiffness of your car? If it rolls at all, the suspention geometry rolls with it, affecting the camber at the tire/road interface. And, a real biggie is the actual geometry of the suspension....does it gain or lose camber throughout its range of motion? How much and when?

What I am trying to get at is that comparing camber requirements between cars is a frivolous activity at best, unless the setups are exactly the same. Same car model and tires are not enough; you must be running the same springs, sway bars, bushings, tire pressures. And, it definitely helps if you have similar driving styles and are running on similar surfaces.

In the final analysis, the best camber at ther road is zero and you are trying to realize that as much as possible when it counts (e.g. cornering). This also goes for the unloaded tires! How you tell what works best is to actually go out to the track and take tire temps. When the tire temps are even across the tread and very similar tire to tire, that is a very good starting point from which you then fine tune things to minimize lap times. There is just no other way to be confident in the setup.

Just my $0.02....

[J P Stein]

Keep it coming, guys. This subject is right up there in my future tire choice quandry.

Obiviously, there is a hell of a difference between 0 camber and -2. On our 914s, it isn't just a matter of turning a few hiem joints to make these adjustments.

A base line set-up must be made (which is a considerable amount of work) just to get close to optimal.

Presently I'm running Hoosier R spec tires that like negative camber (as do Kumhos). Were I to switch to Goodyear cantilevers, which like 0, I would need to make some major adjustments.

Slicks and Rspec tires that like similar camber settings
would be ideal for my situation. Running slicks all the time would turn my car into a trailer queen thus opening up a real can of worms.