JustinL

I'm not sure if this was answered in there or not, but what would have a higher moment of inertia: given equal rolling radius, a 15 inch wheel with tall tires or an 18 inch wheel with low profile tires. I always assumed it was the large wheels/low pro tires that were worse in this category. It seems there are conflicting opinions in this thread.

Justin

Jeff F

Inertia is the principle where an object in motion stays in motion. More weight would equal more inertia in this case. The example would be flywheels. You need to have one, but how heavy?

With unsprung weight, lighter is usually better for practical applications.

Weight would be the easiest variable to look at and control, obviously. That usually points to a weight advantage for larger tires, smaller wheels. Beyond that, it gets complicated. You have factors such as tire pressure and rolling resistance based on weight, contact patch area, and others.

Other factors come into account as well, such as sidewall flex and energy lost due to that. Also remember, top speed cars use the narrowest tires they can get away with due to the exponential increase in wind resistance as speed increases. There is also some tire growth at high rotational speeds in some conditions (dragsters, but the principle applies), especially as tires get larger. This affects gearing and traction.

Justin is basically right if I recall my physics correctly.

There is a ton of stuff to take into account when choosing wheels and tires. Even brake clearance options, and endless others. It is personal choice, and practical choice based on what the goal and the tradoffs are.

Jeff

'86 951 2.8. Lots of extra stuff
'87 928 S4. Some extra stuff
'92 968 Cab. Mostly stock, and staying that way