FIA Rims and Tire sizes, Resurrected Topic

[Buddy Rawls]

FIA cars used 6.5 and 8.5 wheels, with 6.70x15 and 8.20x15 GY Speedway Special tires. When I research those sizes for old 'racing' tires, they come out narrower than 235-60 and 295-50 typical go-to sizing. They came out closer to a 215-70 and 255-60. I know the 6.00x15 and 7.00x15 GY Vintage Sports Car tires shows much wider, but there is no way those could fit properly on a 6.5/8.5 set-up. However, they do fit well on the 7.5"/9.5" set-up. What's the real story? does anyone have an early 60's race tire catalog?

Is 6.70 designation the tread width? meaning sidewall is around 8.5-9 in wide bias designs, perfect for 6.5" wheel.
Likewise, the 8.20 tread would have a sidewall around 10-11 in wide, perfect for an 8.5" wheel.

Just throwing it out there for continued discussion.

The point of this, is determining where to go on my Unique FIA. It has very old 245/60's and 275/50's on it. The unavailability of the 275-50's in a true matching DOT rated tire is the problem. The wheels are 8" and 8.5". A 295/50 is not going to fit well on the 8.5", and I cant go any further inboard because the wheel tire flange is right at the hub 'knuckle', about 1/2" away. The tire area has plenty of clearance inboard but the tire flange doesnt. So, the rear wheel size and position are set. A 255/60 is where I am, leaving a 235/60 up front. But I want a proper stance. So, the front needs to be a 6.5"-7" wheel. The tire choices there, for a proper fit is a 215/70 or 225/70 (too tall).
Both of these seem quite similar to the original FIA front 6.70x15 on a 6.5" wheel. I have seen some of the cars on here with 215/70 and 255/60, how do they handle and how do they look?