I'm looking at some wheel/tire combinations for auto racing, and trying to decide which combination would out-accelerate or have more grip cornering. combo 1: 225/45r15 tire on 15"x8" wheel; 34.2 lbs total weight; diameter 23.0" combo 2: 195/50r15 tire on 15"x7" wheel; 28.4 lbs total weight; diameter 22.7" Because it's a wheel, I don't think an actual moment of inertia could be calculated without some serious CAD drawings, etc. -- just theory here Other things to consider: - combo 1 has an 8.3" tread width; combo 2 has a 7.2" treadwidth. With 1.1" greater treadwidth, you'd think combo 1 would have more contact area, and more grip. However, the footprint on each may be different, since each "may" use different optimal tire pressure due to sidewall stiffness (225x0.45=101.25" sidewall on #1 vs. 195x0.5= 97.5" sidewall on #2). Or is the footprint really different -- ie: would 30 psi inflated tire pressure cause the same amount of tire surface to make the same contact surface area on both tires? eg: If parked on a glass plate and looking at the shape of the contact patch, will x psi cause a different contact patch shape on combo 1 vs. 2? - better cornering is also up for question because of the sidewall deflection, again, a function of tire pressure and also of the actual sidewall height. - overall circumference of tire is smaller on #2, so "gearing" will be lower = faster acceleration - the wheels are 3.3 lbs difference; tires are 2.5 lbs diff. Since most of the weight is towards the outer circumference (the rim of the wheel and the tire itself), combo 1 will have a significant disadvantage to use the car's power. What other info would be needed? Ideas?