And if you go out and measure the circumference of your tyre you'll find it's slightly different to what it calculates to.thanks for the answer, i forgot about tire circumference!! I know when i use that gearing calculator they do ask for the tire size when making calculations.. :thumb:
17" wheel is nominally 432mm diameter (strangely, I've never actually measured one).
190/50 calculates at 1953mm.
180/55 calculates at 1979mm.
I measured new Supercorsa 3's last year.
180/55-17 is 2010mm at 40psi cold.
190/50-17 is 1970mm at 40psi cold.
Worn or underinflated tyres would be smaller still.
I wear one-sixth of the rear tyre mass away from new - that's a kg of rubber.