I'm going to an 18" wheel on the rear of my Z, but I don't want to have to any computer editing. What would equal in diameter to a 275/40/17? If I went to a 285/35/18 would I be ok. What would be the height difference?

Thanks

 

a 275-35-18. That'll do it for ya.

 

..thank you, that's all I need to know...but if I did go to a 285 it wouldn't hurt, would it?

 

No it wouldnt hurt considering the difference in the sidewall for the 275 vs the 285 is barely anything. THey may rub on the front though. Just look out for that.

 

..it would be just out the back, but thanks for your replies and input...

 

I just bought some 245/45/18 all around for my 99 3.8L, and was told they'd fit fine.

I believe you can go up to 285's in the back, or even 295's without rubbing. As far as height goes, I was told by a number of people that going over 18 can be risky (some guy said 20's would fit).

 

...Nice

 

To answer you question....

The stock tire size (245/50-16 or 275/40-17) works out to about 25.65" diameter.

A 275/35-18 is 25.58" diameter..... causing the speedo to read 2/10 mph high at 60mph.

A 285/35-18 is 25.85" diameter..... causing the speedo to read 1/2 mph low at 60mph.

Niether of these speed errors is worth "reprogramming" unless you just happen to have a HPP or LT1_Edit handy..... .

All of the dimensions are "theoretical", to the extent that there is a little variation from manufacturer to manufacturer, and even within different tire lines from the same manufacturer.

 

...that's exactly what I was looking for, I do however have a HPP3 for my A4 issue, is there a setting on the HPP3 for 18" wheels? on the rear ofcourse.

Thanks