Robert Green

Hi All, thanks for the feedback on my earlier questions about upgrading my wheels/tires from standard. I am looking for suggestions on tire size.

At present I am running stock 14 x 6 wheels with 215/75R14 rubber. Checked against satnav, my speedo reads 72mph at a true 70.

I am planning on a set of 15 x 7 Vintique SS1 wheels. These come with a 4.375 inch backspace.

What size tires will work with these? 225/70R15 look like a pretty good match to overall diameter, so would 225/65R15, though a 65 aspect ratio is harder to fine, especially in whitewall or raised letter.

235/60R15 would be okay diameter wise probably, and would be a bit more aggressive. Would I get any clearance problems with these?

Any thoughts gratefully received!

Robert Green

joe_padavano

Do the math. Your 215/75-14s are 26.70" outside diameter, which is very close to that on the OEM tires. Your suggested 225/70-15s are nearly an inch larger in diameter at 27.40". If you plan to keep the same outside diameter, 245/60-15s are 26.57" OD.

Oldsguy

The previous owner of my '72 Vista Cruiser put 15X8 steel wheels with 215/70R15 tires mounted and they clear all around with no problems even on the front from full steering wheel lock right to left. The wheels have a 4 inch backspacing and 5 inch frontspacing. I know that 4+5 equals 9 but I measured from outer edge of the wheel, not the tire bead edge which is what I think where the wheel size comes from.

Robert Green

Thanks guys. Joe, as it happens - at least according to tire calculator.com - the 215/70R15 would compensate approximately for the slight over read on my speedo.

So the 245/60R15 wouldn't give a clearance problem on a 4.375 inch backspace wheel?

joe_padavano

I'm curious as to why they would make a 7" wheel with 4.375 backspace. 3.75" backspace would be about zero offset, which is what you want. I remain frustrated that wheel manufacturers list backspace and not offset, which is what matters. In any case, I ran 255/60-15s on OEM 15x7 SSII wheels on my 69 with very minor rubbing in front if I hit a bump at full lock. The 245 should be no issue.

OLDSter Ralph

Joe P. (and others) The "backspace dimension" does have some value. Generally "people" run tires that are wider than the "bead width" (measured wheel width) and backspace, so the backspace becomes a reference. Some wheel manufacturers list both offset and backspace. Tire width is what causes interference, more often than not.
"Backspace" dimension can include a thicker material and the curvature outward from the bead. You can more easily measure from the edge of a bare wheel to fenderwell for a general reference. Rear end differential width is an unknown until drum to drum width is verified. But, until you mount a "loaded" tire/wheel combination and run a bare hand/fingers around the tire sidewall to check, its kind of a guess.

I went through all the calculations with my "Drag car" (Resto-mod project). In the end, a 15 X 8 (zero offset) wheel and inflated 2.75/60R-15 tire was mounted and loaded (car sitting on the ground). Running my hand around the inside between the tire sidewall and wheel well told me I had no problem. Then, I mounted a 15 X 10 wheel with 3.25/50R-15 inflated and loaded tire got the hand check around the tire sidewall.

It seems to me that "0" offset wheels will likely work most of the time. The tire size is the huge variable.