I bought new wheels for my 05 GT 19x8.5 int the front and 19x10 in the rear. My question is is there a formula for figuring out tire sizes or does anyone know of some tire sizes the will work well. My car alson has eibach springs. Thanks for any help.

 

Tirerack.com is your friend.

 

It depends. Do you want to keep stock tire height so you don't need to recal your speedo? If so I suggest 255/40 in the front, and 285/35 in the rear.

 

Here's 2 spreadsheets. Save them and rename to .xls
RPM v Speed has the tire size tab in the spreadsheet.

 

You may wish to add a small correction factor to the formulas. The effective rolling radius of a tire lies somewhere between the unloaded and loaded radius. A pretty close factoris 3.5% more revs for any speed calculated based on unloaded tire OD (or speed = 0.966 * speed based on unloaded OD). The reason is that the tire treadcompresses ever so slightly in the circumferential tread direction as it passes through the contact patch - not as the direct consequence of and as a linear function of loaded radius as is sometimes believed.

The difference is not a huge deal, but it might mean something to anybody looking for a specific true speed at (say) engine redline or attempting to correlate speedometer and tach readings.


Norm