Will 255 40 18's in the rear and 225 40 18"s in the front be the best approach?

 

255/35-18

 

Yes, what RT wrote!
I'm running that same setup....225/40-18 in front and 255/35-18 rear.

 

ok im trying to settle on a size myself, a friend of mine who races told me to stick to 215 on front? Any opinion on that I was gonna go 215 40 front, and 245 35 rear....but I might go with 225 40 front..255 35 rear.
One other q...another "car" guy told me to stick with a 40 series all around and not 40/35. I do not understand why either way...why go with 40/35 over 40/40 and vice versa..

thx in advance for your inputs

 

No reason not to go 225 in front.

You really need to use tire diameter to determine your aspect ratio. If I remember, the stock sizes are 24.8" front and rear (although don't quote me on this memory.) You'll want to keep this diameter on both ends. Mathmatically a 255/30-18 is 24.02" and a 35 aspect tire is 25.02. But you really need to check the tire specs provided by the manufacturer as the math varies quite considerably from the manufacturing.

Try to keep the fronts and rears within say .5" in diameter, the closer the better for ABS. If you need to decide, a smaller overall diameter is quicker (it changes the effective gearing) at the expense of mileage and top speed.

Oh, and here's the formula:
tire width in mm x aspect ratio decimal [.40 for 40 series] / 25.4 [inch conversion] x 2 [tire height twice] + wheel diameter [in inches] (ie. 255mm*.35/25.4*2+18"=25.02")