'04 G35 Coup w/ Sport Pkg. I want to increase the width of my rear tires when I replace them. My local tire dealer told me I could upsize from 245x45-18 to 275x40-18 on my stock rear rims with no problem and that the diameter would change very little from stock. The Miata tire calculator seems to support this..but I haven't found a thread that supports this. I still have 225x45-18 fronts which do not need replacing anytime soon. Any advice?
BTW, I spent about two hours searching threads. If I have missed one that address this please let me know.

 

You'll be fine. The lower sidewall rating with the wider tire will make sure your VDC doesn't go crazy

 

I don't think that sounds right for an 8" rim since I'm running 275s on a 10" rim and it's like perfect. I wouldn't go any larger than 255/40ZR18, there's no real advantage of going that wide on your rims. Looks, I doubt when installed you could tell the difference between the two except with the 275s you might have tire buldge....not good! When you need to replace the fronts you could easily go with 245/40ZR18s for far better control. I dislike Nissan's idea of using that small a tire on the front end where 52% of the weight is....my .02cents.
Gary

 

Thanks for the advice. This really gets confusing for a tire novice like me. Anyone running the steup I'm talking about? I'm just looking for a wider rear tire without problems.

 

I would run 255 on the rear, anything higher than that is just not worth doing...

 

275 will help avoid curb rash. My .02 cents.

 

I wouldn't run a 275 tire on an 8" wide wheel. Too much center bulge could lead to accelerated center wear and possible poor handling or VDC problems. Recommended rim width for a 275 tire is 9-11"

 

I have 295 with an 11"
works for me....