Quote Originally Posted by DennyW
...As you can see, the larger tires reduce your final drive ratio to 3.30—a measurable difference. You can also do this to determine the effect of smaller tires on the final drive ratio...
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I am too tired to crunch numbers today but I believe, and correct me if I am wrong, that changing tire size does not actually change your drive ratio or gear ratio (if you are using those terms synonymously). If you change tire size, and hence the circumference, it has the "effect" (performance wise) of changing your gear ratio.

It's an easy way to change the performance of your ride (for people like me who have never tore into a rear end ... ) as long as is doesnt negatively impact the appearance of your ride.