TIres and speedometer problem

[marek]

I heard that when u get bigger or smaller tires than the speedometer either shows u going slower or faster, does anything mess with the tachometer, or does that stay the same and exact?

 

[GSRCRXsi]

yea it doesnt mess with the tach. but depending on how much smaller/bigger your tires are from stock your speedo will be off. for example, when i race at the track i run a 205/50/14 tire, thats significantly smaller so my speedo reads like 100 when im only going 90. also tire size changes your final gear ratio

 

[wanderinman]

Tire Size Calculator

... I'm going to start keeping track of how many times I post this thing, its been at least 10. And he's right, your tach feeds of an electrical signal from your ignition, not anything to do with your wheel speed.

 

[vansterdam]

Here's another good tire size calculator