Drivetrain Math Help

[BrockSamson]

OK, for the most part when people put bigger wheels on their cars, they don't consider the fact that it makes you slower. I know it doesn't make you really, really slow but I would like to go the speed I see on my speedo. One way is to get a new set of gears, but in order to get the correct set, there's a formula that involves the size of your new wheel size. Does anyone know what it's called and what numbers go where?

[180fan]

http://www.miata.net/garage/tirecalc.html

[corn322]

when a lot of people get bigger wheels, they get tires with a shorter sidewall, so the overall diameter is the same, and the speedo is correct.