Hi guys. I am buying some new rims for my 8. Here are the options I am considering

18x8.5 all the way around with 245/40/18 nitto 555

or

18x7.5 front nitto555 225/45/18
18x8.5 rear nitto 555 245/40/18

Does anyone know where the speedometer gets its speed? Front or rear? Because going with the 245/40/18 will put me about a half inch shorter, and I don't want the spedometer to be off too much.

Thanks for the imput guys... let me know what you think.

Slavearm

 

Okay - Nitto 555 are crap tires. Your original RE-040 tires will handle better, have better grip, and ride better too. Also, staggering the tire sizes (especially going to different diameters) will screw up the handling, throwing off the balance designed into the car and introducing more understeer. Unless you're re-engineering the suspension (spring rates, anti-roll bars, and shocks) to compensate for that...

Regards,
Gordon

 

This Tool deserves an Award. :D

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

 

Yes that is a good tool, but one note in case anyone is doing any kind of speed, power, RPM calcs; the radius, diameter, circumfrence, and revolutions per mile are not entirely accurate. They are based on a tire that is not on a car, i.e. without any weight on it.
Actual dimension are about 4% less which is not a big deal but for instance the revolutions per mile it says the stock 225/45 R18 tire is 777 rev/mile when the actual load rev/mile from the manufacturer is 804 rev/mile. Radius on web site is 13", actual static load radius is 12.1" Probably useless information for most but FWIW here it is.

-WN