My stock '56 Chevy's tire size is P215/70R15. I found some P225/70R15 tires in the cl***ifieds. Could I use the 225s without a problem? Here's a cross reference tire chart: http://widewhitewalltire.com/CrossChart.asp
The 225's will be less than 1/2" wider and just over 1/2" taller. If you mount them on the same rims the 215's are on, that's less than 1/4" extra width both inside and outside the wheel wells and just over 1/4" extra static radius to the tires. You won't have a problem. Steve
I'm running 225/70R15's on my '56 with American torq thrust originals.(tto's)15x7,and have had no problems.I think it cross references to a G-70 wide oval we use to run in the late 60's early 70's.Fills up the wheel wells with no rubbing.
Your Chevy originally came with 670-15s, and the closest radial size to that is actually 205/75R15. Still, I think the 225/70s will fit and look fine.