Wheel & Tire Size Relation to Torque/Power

Would having a big wheel like say 25" and up affect your torque/power in your car to actually lose torque? I think I would find it pretty obvious if a monster truck with a huge amount of clearance had 80" Tires I think it would loose some torque at the tires and wheels. Although it would cover more ground...

Would the same be for the opposite? If you would have 10" tires would you have to use more power to cover more road? Would that also mean losing power?

Anyway how does a tire's size affect torque? Would would be the best size for best performace in a car?

I think what you are getting at is will a larger tire cause you to lose power...Yes it will..a larger tire causes more drag on the car, requiring more power to push the car..a tire that is too large will also slow the car down in turns. You may have a larger contact patch but the the weight of the larger tire acts with the centrifigual force to push the car out.. As far a gearing a larger diameter tire will make a taller ratio..taking velocity away but giving you a higher speed per rpm..a 10" tire will give shorter ratios..you will get up to sped quicker but you will not have a good top end.. In my experience I have always kept the same diameter tire as stock..just moved up in width to get some more traction...changing the diameter too much on the front end changes the steering and suspension geometry and may cause the car to handle worse than it was stock.

Increasing your O.D. will have the same effect as changing your gear ratio on the back end of things. It will tend to make the car feel very sluggish on the bottom end (off the line and around town in stop-and-go traffic). With most newer cars you don't want to go more than about 3/10" larger or it will affect the ABS, fuel mixture, and even shift points on the tranny for automatic cars. You can sometimes go wider to gain better stability but I would stick with the stock O.D. or within 3/10". The increased weight of many wheels/tires in the larger diameters will also make for more stress on the tranny and brakes. For most cars, 17" or 18" make the most sense for true performance upgrades. Anything bigger is just eye candy.

So say i have a stock 14" or 15" rim i could go up to a 17" with out any change in performance of my car? Does the actual diameter change or is it just the rim have a larger diameter and the tire is shorter so it comes out to the same diameter of the whole package of the stock?

When you plus size correctly, the O.D. will remain the same. Typically you will end up with a slightly wider tire and a shorter sidewall. The wider contact patch and limited sidewall flex will give you better handling, steering response, and stability. The trade offs are that you will have more road feel and a little more noise.

will this also stiffen the cars ride since there is a stiffer wheel and tire?