So your goal is what figure out tire specs for your wheels to get .... If you are low a taller tire will rub .... Post a picture of your car and tell us if you have a drop , if so how high is the fender to the floor ??? I'm assuming you want hide some wheel gaps as well ...

 

I run 255 michelin pilots on the back of mine and it looks good, no probs at all.

 

Pics^^^

https://g35driver.com/forums/media-s...s-g-sedan.html
Here are pics of my car..

Front has a little wheel Gap. Rear really doesnt have any.. and taller of a tire and I think I would def rub..

 

Bump for more input..

 

It is important to keep the overall diameter of the stock tire when changing tire sizes. For instance, if the overall diameter is 2" + 18" + 2" = 22", then you want to be within 3% of 22" with any tire change. The higher percentage of change, the worse it is for your transmission and various computers attached to your power-train, including your speedometer's accuracy.

Some math...
Say you choose a tire that makes your overall diameter lessen from 22" to 21". To figure out the % the tire is different, do the following:
(21/22)*100=95.45% . 100-95.45=4.55% off.


So, how do you determine the overall diameter of a new tire? Using the section width (i.e. 245) and the aspect ratio (i.e. 40). The section width is the width of the tire in millimeters. The aspect ratio is the percentage of side of the tire compared to the width. So an aspect ratio of 40 on a 245 tire is 245*.40=98mm.

Stock size is 235/45/18. Overall diameter is 18" + ((235*.45)*2) = 18" + 211.5mm = 668.7mm.

245/45/18 = 220.5 +457.2 = 677.7mm . 677.7/668.7*100 - 100 = 1.3% greater than stock

245/40/18 = 196 + 457.2 = 653.2mm. =97.7-100 = 2.3% less than stock.

So 245/45/18 would be a better choice. You will have more sidewall (about 1 cm more) than stock with this one, and than with the 245/40.

Before buying tires based on this calculation search for tire size calculator to verify I set up my equations right and did my math right. I did not double check it.

 

PS, read up on plus sizing (including +0 which is what you are doing) and other tire information at www.tirerack.com and www.discountiredirect.com

 

Are you sure 45 wouldn't rub tho because of how low i am..

Edit. So I used the calculator and came up with 40 is 5 percent different.. While 45 will make it 9 percent different than the stock tire.. Wouldn't 5 percent be a better choice.. I just don't wanna buy a tire that will have to big of a sidewall and hit my fender..

 

Good info here.

My stock size was 235 40 18 (I think)

I ran 245 45 18 on stock rims and it put my speedo off by about 1.5 mph.

Now I run 19" rims but my tires are 245 40 19's and my speedo is perfect. The 235 40 18 and 245 40 19 have the exact same diameter so though I have bigger wheels and tires, I still have a stock rolling diameter and my speedo is correct.