17 to 18 inch rims, speedometer off,how much??

[GeorgiaGT40]

How much would changing to 18 inchers from 17 mess up my MPH?

 

[Mustang5L5]

It won't if you keep the outside tire diameter the same.

 

[GeorgiaGT40]

I'd be going from a 245/45/ZR17 to a 265/35/ZR18..


had a typo, I meant 245/45

 

[Cobra Jay]

It won't if you keep the outside tire diameter the same.

Click on the link. Then click on calculators and figure out your tire height.
www.randysringandpinion.com

 

[Mustang5L5]

I'd be going from a 245/75/ZR17 to a 265/35/ZR18..

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

You would be off a bit.

I would suggest a 275/35/18 out back, It will keep your speedo close. it will only be off 0.4%

 

[GeorgiaGT40]

It says I will go from 31.468503937007874 to 25.30314960629921 in tire height....

 

[GeorgiaGT40]

...not too bad off

.9 mph off