forgive me if this question has been asked and answered previously but i have heard that the arger the rim you put on the more it throws the accuracy of your speedometer off. Myth or truth? i can see the mathematics behind it, but arent cars designed to take this type of **** into consideration as in having the speed sensor in a place where something like this wouldnt mater?

 

No.

Generally when you go up in wheel size, you get a smaller profile tire to keep the overall radius the same.

For example, OEM SE 16 tire size is 215/55R16. If you go up to a 17 and want to keep the same section width, you'd go for a 215/50R17 tire and it would be similar enough to the rolling radius of your old tire that you would not notice the difference. You could also go for a 235/45R17 or a 255/40R17 and the diameters would be similar enough that the difference would be negligible.

If you fail to do this to a certain extent your speedo and gearing will be off.

 

wow, i shalln't lie. OF all of the conversations i have had with people about this, not once did your explanation ever come up. That makes alot of sense. I am a dumbass. Very smart u r.

 

Gotta love physics.

This should come in handy for you.

Speedometer Calibration Calculator

 

Awesome meng thanx, what part of the valley u from mik3

 

Yeah, no problem. I'm a Glendale local.

 

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

done.

 

Most speedometers are calibrated to be 1-2 mph faster than the actual speed (eg shows 67 mph, your actual speed is 65). This is confirmed with GPS units.

There are times when you upgrade that the correct tire size is not available. Plus, some people that upgrade want a bit extra sidewall protection, so they'll purchase a size slightly larger than the original. Just keep it within 2% and you should be fine.