Will 245 work on a 17x7 +38 wheel?
 

It'll be for the rear for my FC. Just to let u know, I'd like to do this because I wanted to make my rear look wider. Any ideas?

No, 245-mm widths require at least an 8-inch wide rim. Do the math--245-mm converts to 9.64 inches:

245 mm x 1 inch/25.4 mm

multiply across, mm dimension cancels, and you're left with 9.6457 inches!

OK, now you try it...

How many inches would a 255-mm width tire be?

Hmmm... you can't just directly do the math on tire fitting. How would you explain a 225mm tire on a 7" wheel?

To maintain stock wheel+tire diameter, you would need to run a 245/40 17 tire. The minimum width for this size is 8". If you went with a 245/45 17, you would be taller than stock and would still require a 7.5" wheel. Note these are the MINIMUM recommended widths, not ideal.

Ideal width is about 90% of tire width.

Go to www.tirerack.com and look at potential tire purchases. Under the spec section for each tire, it will list the recommended rim widths. You will find that 225/50 is about as wide as you really want to go.

Yeah, what rynberg posted:)