Tire Profile design

[92 white 0650]

Trivia question: I know 99.99% of you don’t care about this because low profile tires just look fast and sexy and that's all that needs to be said, :wink: but what controls tire profile/sidewall height in the design of the tire/car combination? Why do sports cars on the track (ALMS or DP) have large diameter wheels and low profile tires but formula cars have small diameter wheels and tall sidewalls? Don’t both types have similar performance and chassis/suspension design with sports cars carrying a little more sprung weight? If there’s an unsprung weight advantage to the formula combo, why wouldn’t sports cars follow suit? What’s the theory?

 

[docjohn]

afaik with formula cars,the tire is a more important component of the suspension than in sports cars.The tall tires of formula cars acts as an additional spring,allowing for stiffer shorter springs and thus reducing the need for excessive shock travel

 

[jcjcf1]

I follow Formula 1, and I'm not absolutely sure of this, but I think the F1 regulations require the tire configurations that are used and the teams cannot therefore run lower aspect ratios. ALMS, I believe, allows the teams some latitude in tire choice.

 

[Shumdit]

I follow Formula 1, and I'm not absolutely sure of this, but I think the F1 regulations require the tire configurations that are used and the teams cannot therefore run lower aspect ratios..

I think this is correct also

 

[92 white 0650]

with formula cars,the tire is a more important component of the suspension than in sports cars.

I think you're on the right track Doc. Is that part of what's called wheel rate? Someone else used an anology of a tall pencil eraser; it will flex but still stick and drag tires are tall and flexible for max grip. I can see an obvious difference in formula car suspension and traditional sports car suspension, but I thought the ALMS types were pretty close to formula car layout. Maybe that's not right.

The statement of rules is correct; F-1 is very tight on wheel and tire diameter, but since high aspect ratio in formula cars is traditional, I don't think the rule is aimed at limiting performance, it's just a standardization thing.

Anyway, I thought this would be a quick exchange, but no one's put it all together in a nice easy "one beer" answer.

 

[Gansan]

I think you're on the right track Doc. Is that part of what's called wheel rate? Someone else used an anology of a tall pencil eraser; it will flex but still stick and drag tires are tall and flexible for max grip. I can see an obvious difference in formula car suspension and traditional sports car suspension, but I thought the ALMS types were pretty close to formula car layout. Maybe that's not right.

The statement of rules is correct; F-1 is very tight on wheel and tire diameter, but since high aspect ratio in formula cars is traditional, I don't think the rule is aimed at limiting performance, it's just a standardization thing.

Anyway, I thought this would be a quick exchange, but no one's put it all together in a nice easy "one beer" answer.

Wheel rate refers to the spring rate as measured at the wheels. This takes into account all the various linkages and leverage that you get acting on the springs, depending on how everything is mounted.