I'll be getting my new Touring AT Z in a few days. My first Z. There's alot of posts I've been reading concerning tire size. Unfortunatley, the automatic touring only is available in 17's. If I want to put 18's on it like the manual touring, will it void the warranty in any way and is it a good idea at all. Does it make that much of a difference? Thanks in advance

 

No it will not void the warranty.

If you go from 235/50-17 to new 18" wheels with 245/45-18 tires your speedometer will read 1.6% too slow (which is acceptable). When your speedo reads 60 MPH you will actually be going 61 MPH.

Play with this calculator:

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

 

Thank you.....appreciate the help