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Yet another tire question...

xbnb1978x

xbnb1978x

New member
I have an 08 Grand Prix . I just bought a set of rims Size: 18x8 Offset: +40mm ... What is the best tire size that will fit on my rims so they wont rub the fender or sidewall? Im trying to get them as fat as they can go and as low to the ground without a problem. Thanks!
 


Help me out, im a newbie "idiot" when it comes to this stuff...

Rolling diameter?

Tire Size XXX/XXX/18 are you talking about the middle number when you say rolling diameter?

Would the first set of numbers XXX be the width or the height of the tire?

Would the second set of numbers XX be the width or height of the tire?

Im not to worried about my speedo changing I have a Nav system that tells me how fast im going. Thats should give me the correct MPH speed Im at...

but if thats going to mess it up that much. what would be a tire size you would recommend...?
thanks
 
Rolling diameter is if you measured the actual diameter of the tire. This distance translates to so many revolutions per mile. If you change that, you have just thrown off your speedometer. It's not represented by any number on the tire, so you have to do the math to figure it out.

Or you can use a handy tire calculator:

Tire size calculator

Input your old tire on the left, and new tire on the right.

245/40/18 will throw you speedo off by 3.4%. When you're traveling 60, it will read 57.9 and the difference will get bigger the faster you go. The tire is too short.

245/45/18 is almost exactly the same height as your current tires and the difference is so small you will never notice.
 


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