Just digging around online and came across this site that does tire size comparisons:

https://tire-calc.com/comparison/225...5-60-r15-inch/

You all know more than me, I’m just wondering if I can trust their calls. Do they look reasonable to you all?

Thanks
Chris

 

Yes it's probably correct, I use the one on Discount tire. There may be a small difference between tire manufacturers.

 

I wrote my own in Excel. I find that these calculators are frequently all over the map. Also keep in mind that sidewall flex changes the effective rolling radius. Radial tire sidewalls flex more than those on bias ply tires, so even if the theoretical diameter is the same, the radial will have a smaller effective rolling radius. Also note that tires with shorter sidewalls have less sidewall flex, so even though (as an example), 275/60-15 and 275/50-17 have nearly the same theoretical diameter, but the shorter sidewalls on the 17" tire (5.4" vs 6.5") will result in a slightly larger effective rolling radius than for the 15".

 

I was surprised when I put a yard stick against my tire and saw it was quite a bit shorter than what the manufacturer's spec showed.