1967 GTO wheel and tire size question....mainly rear backspacing for large tire.
 

To run a 245/60 -15 or a 255/60-15 rear tire on a 1967 GTO on a 8 inch wide rim what would be the correct backspacing to make it so tire will not rub on wheel opening? I know we tried a 8 inch rim with 4.25 backspacing and tire will rub. These are Cragar SS Mags and I would thing around 5 inch or so backspacing would work but I believe 4.25 is max with Cragars? The car does have rear disk brakes, and maybe the disc conversion widened it out some?

PS there is a lot of room between tire and frame..around 2 inches. American Racing VN405 Custom Torq-Thrust II Chrome with Polished Barrel Wheels C405586147 has a 15x8 with 4.75 backspacing...link is here https://www.summitracing.com/parts/are-c405586147 I would think this would work great with a 245/60-15 with no clearance issues???

On my 66 Tempest, I'm running 275/40r19's on 19x9.5 wheels that have +35 offset in the back and a 10mm spacer. An online calculator says that's 6.25" of backspacing. I have 1.125" of room at the lip but the wheelwell gets narrower as it goes up, so it's closer than it sounds. Ballparking here, let's say there's 6.5" of backspace room and 4" of frontspace room-- 'ish.

Those 4.75" BS wheels would give you 3.25" of frontspace-- same as mine. Mine are a little snug and there's some play in the rear end on hard cornering, despite having aftermarket suspension. I have rubbed the back tires but most of the time it works well.

I worry that you're going to have sidewall bulge on a 15" rim that I don't have on my modern setup. That might rub, but you're probably fine. If you can find a rim with more backspacing, that would allow you to run spacers as-needed. Either that or find somewhere/someone that'll let you 'try on' the 4.75 BS wheels+tires.

I know the modern look isnt for everyone but classic tires have ****ty traction under braking compared to normal BMWs and stuff now. That's why I went with them. They're only available for bigger wheels. Those wheels are designed for BMWs in our bolt pattern, so I acknowledged that I would need to run spacers. -- all that to say the spacers I needed weren't what I had measured out. I wound up needing less than anticipated to give me more backspacing. I'm really glad I was able to buy different spacers instead of all new wheels.

Just my 2c.

On my 67 GTO with the original rearend (60 3/4” flange to flange) I had to go to 5” BS to fit a 15x8 wheel. It was centered but I did (very) slightly clearance the insides of the quarter panel pinch welds. At the time I was running Pro Trac tires (275-series equivalent, not sure if they even make them anymore as I think they have changed since as that was in 2002). Hope this helps.

67 GTO 17x8 wheel 5.5 backspace 255/45 17 26.1" tall, no rubbing......245/60 15 is 26.5 tall so that should give you an idea of what you will need

4.75" or 5" backspace will work best on an 8" wide rim.

Depends also if you have, or plan to add, rear disc brakes as that could increase track width - and then 5.25" or so backspace is typically needed.

I run that tire size as well.
My rear rims are 4.5" BS. They clear - almost.
If I have a big guy in the rear, the passenger side will rub the tire a little.

4.5" was the only option I had on my rims. A little more would be perfect. My car the passenger side and the drivers side has a difference.