Just curious if there were any formulas available that would be able to give torque loss with increasing tire diameter. There are so many great tires availalbe in 205-55-16, and not so many great ones in 205-50-16 (better size for the MINI). The average tire is 24" for the MINI, however, the former is 24.8", exceeding the plus or minus "3% rule". So, would I even be able to tell the difference in performance between the two?

 

well i'd be more worried about rubbing then torque loss. someone in the local club is running 205/55/16 because the tire shop sold him the wrong size. you can clearly see the rubbing on the shoulder of tire, suspension is standard cooper s.

 

I'm really surprised there would be rubbing with less than an inch difference in diameter between the two. Furthermore, it seems that quite a few are driving with the larger size tire. Are you sure it was this size?

 

Not surprising that they rub. When I had my tires rotated, I talked to them about possible alternate tires instead of the 16" runflats. The clearance between the tire and the strut is tight, it was hard to get a finger in there. He was worried about anything larger than the 195's.

 

??? OK, You're talking of 195. That's width, not diameter. We're talking about diameter.

 

You have to consider both the diameter and the width. A 205/55 is both taller and wider than a 195/55. A 205/50 is close to the same height, but wider, than the 195/55. If you look at the suspension, nothing is vertical, so where things bulge makes a difference. If you have a stock suspension, I do not think that the extra diameter would make cause a problem.

We have another car which came stock with 205/60-15 tires. We installed a lowering suspension and had no problems. We then added wider wheels, same offset, with the same tires, and now have a rubbing problem.

 

>>I'm really surprised there would be rubbing with less than an inch difference in diameter between the two. Furthermore, it seems that quite a few are driving with the larger size tire. Are you sure it was this size?

i'm positive on the size.

 

Thanks for replies. I guess I knew all that. I just wanted to know if there would be any noticeable torque loss with the 205-55-16. Then, minhi says there would be rubbing on standard suspension??

Intuitively, I would say that the torque loss experienced when playing around with wheel/tire diameters would be directly related to the change in % diameter. So, if going from a 24" to a 24.8" diameter wheel/tire, you would experience a loss of 3.3% since torque is a measurement of length x force. But, after thinking about this, (going back to simple machines), I belive this would be an example of a 3rd class machine in which the force is between the fulcrum (axle) and the load (perimeter of tire). So, the above "formula" may not apply.

In actuality, the amount of torque a car is able to generate is equal to the internal force applied to the axle MINUS the torque in the reverse direction at the perimeter of the wheel, a function of pure friction when the car is perfectly level. So, when you increase the diameter of the wheel, you increase the negative term of the equation, and an increase in diameter would NOT be directly related to a loss of torque (linear equation). So, can anyone say for sure which is the case?

 

I'm not sure about your formulas, but a change in diameter does affect the gearing. Smaller than stock causes SLIGHT lower gearing and taller = SLIGHT higher gearing. In normal day to day driving you'd probably be hard pressed to notice the difference.

In autocrossing the difference is more easily seen. A stock MCS can benefit from higher gearing because it 's so easy to spin the the front wheels and apply the power you have. A MCS with a Limited Slip installed benefits from lower diameter wheels/tires -- here you want the car geared lower because you can apply the power to the ground

On the street you more worried about rubbing and the speedometer reading high or low when go lower or higher in your diameter