[re-rx7]

Originally Posted by kn7671 Wrong. Wheels have absolutely no relation to gear ratio. Tire diameter effects gear ratio, but you can choose tires for larger wheels that have an equal tire diameter as stock 17, 18, or 19's in 20" sizes without affecting gear ratio. That being said, if you choose tires with different diameter than stock, say approx. 3/4" shorter or taller, the effect on gear ratio is minimal, about 3% on average. At 70mph you'r speedometer would be about +2mph with smaller tires or -2mph with larger tires. You don't lose power if the overall weight of your 20" wheels/tires are the same overall weight as the stock 18" or 19" wheels/tires, which isn't too hard since the factory wheels are usually on the heavier side.

At that point you will sacrifice ride quality. Thats why if the car is lowered 18's seem to work fine.