It's getting harder to find quality tyres for older cars. There was a time (not too long ago) when 14" and 15" diameter wheels were common, I remember thinking that having 15" wheels was cool. Now those sizes are almost gone, even entry-level modern cars use 16" wheels, and 18" and larger sizes are the norm. As a result, tyre companies just aren't making the older sizes any more, the market for those tyre sizes is too small.
Most Corvette owners running 15" rims (like the Kelsey Hayes knock-offs on the Red Rocket) are fitting taller tyres for a period-correct look — typically 70 or 75 profile radials. From the factory the Kelsey Hayes wheels would have been fitted with 7.75x15 bias-ply tyres (we call them cross-plies or 'razor blades' in Australia). These tyres look skinny by modern standards, and their sidewall height is equivalent to about an 83 profile — much taller than 70 or 75 profile radial tyres.
There are some specialist tyre makers (like Coker) making reproductions of vintage tyres, but they're hard to find in Australia, and extremely expensive to import. If your Corvette is a 'driver' you're going to want a tyre that's rated for high speed, and offers decent performance (braking, handling etc…), these reproduction tyres offer questionable performance, they're really more 'show than go'.
Do a quick online search for 70 or 75 profile 15" tyres, and you'll find almost nothing but light-truck tyres. These are the sort of tyres you might use on a trailer, not a sports car! In Australia, only 3 companies offer a white sidewall 15"; Sumitomo (Japan), Maxxis (Taiwan) and Mastercraft (USA). The Sumitomo and Maxxis are hard to find, and COVID-related supply-chain problems seem to have made it even harder. That leaves owners of older American cars who want white sidewalls with only one choice — Mastercraft. Mastercraft are an American company (owned by Cooper), but all their 'old-school' tyres are made in Mexico now (possibly in the same factory that make tyres for Coker?).
When I bought the Corvette it had Mastercraft white sidewall tyres on it already — 215/70R15 on the front and 225/70R15 on the rear. These tyres looked quite 'fat', particularly the rear ones — the owner who fitted these tyres had been running 15x7" wheels (pictured below), so he'd fitted wider tyres. They were old too — the rears were over 10 years old. With the car off the road in 2021, I decided to take the wheels off, clean them up and fit new tyres.
When I started looking I found that Mastercraft don't make the 70 profile any more, 75 profile was my only option. The relationship between tread width and sidewall height means that a 215/75 tyre will be taller (i.e. have a larger diameter) than a 215/70. To maintain the same tyre height, I would need to get slightly narrower tyres.
I was able to find Mastercraft 205/75R15s for the front and 215/75R15s for the rear. I actually prefer the look of these tyres, they're a bit skinnier, they fit the Kelsey Hayes wheels better and I think they look more 'period-correct'. I also like having a slightly wider tyre on the rear, the difference is very subtle but it looks good on the C2.
I've had the new Mastercraft white sidewall tyres on the car for more than 6 months now. I purchased the tyres in 2 batches from different suppliers — the fronts first and then the rears. The production date on the tyres showed that the 'new' fronts were actually a year older than the rears (2020 production versus 2021).
When I washed off the blue protective coating I noticed that the white band on the fronts was already showing some discolouration (a slight yellowing on the outer edge of the white band) while the rears were perfectly white.
I wondered at the time if this was due to the age difference, and sure enough, after 6 months of use the rears have also developed the same discolouration. Do all white walls do this, or is is just the Mastercraft tyres? I'm inclined to think this is due to inferior materials or manufacturing, it seems I'm going to have to learn to live with it.