tyre size advice for a 60-66 C-10 truck needed please.

[disasterbus]

Hi all,

Can anyone tell me the standard tyre size for a '64 C-10?
I'm trying to find out the overall tyre height on a standard truck (when it left the factory). I appreciate it would have had cross-ply tyres on then, not modern radials but I want to get the tyre height (and therefore the rolling circumference) about right so the gearing is as it should be.

I think it would have had 30" tall tyres - is that right?

My truck has aftermarket 15" wheels with 275/60x15 tyres on the back and 235/70 x 15 tyres on the front.





I think that originally the tyres were about 30" tall on the stock rims.

My rear tyres are only about 27.5" tall and the fronts are about 27.75" tall, so the gearing is way out, it revs higher than it should at higher speed, and I guess the speedo is not accurate either as the circumference of the rear tyre is currently 86.35", whereas a standard 30" tall tyre would have a circumference of 94.2".

The current tyre is therefore only 91.67% the size of the original - does that make sense?

I was going to fit some 16" wheels I recently bought (which came off a 1961 C-10) but think I can keep my wheels instead and fit narrower, but taller tyres.
I'm thinking 245/ 70 or 75 x 15 on the back,
and 235/ 80 x 15 on the front. - both should give an overall tyre height of around 30" according to my calculations

Just need confirmation that the originals were about 30" tall - can anyone confirm?

Thanks!!

[1963c-10]

Factory tire chart for 65/66 (closest I had to 1964).

I run a 235/75R15 all the way around and really like the height/stance of the truck.

A 205/75R15 or 215/70R15 would be the closest to a factory tire that you'll find in a radial.

[jayoldschool]

Yes, the tires back then were really small. The tires you are running out back now are taller than stock, so you are actually revving less than when it was new. We're just used to low revs/overdrive transmissions.

I also run 235 75 15s on my 65.

[1976gmc20]

Our family bought a C-10 new in 1966.

I don't remember the exact tire size, but they were 4 ply passenger car tires and a 2 ply spare, probably G78/15 or H78/15 (I don't remember if they used the letter sizes then or the even older number sizes like 8.25x15 which don't relate to any modern measurement that I know of).

We had a heavy shell camper on the pickup and after numerous tire problems my mom bought new 7.00x15 Firestone "Transport 110" 6 ply truck tires for it which worked great (the 7.00 means 7" width at sidewall, and the aspect ratio back then approached 100% so that makes them almost 29" tall)

LT235/75R15 would be the modern day equivalent but of course they are quite a bit wider than the 7.00x15. At least that is the size that was recommended when I first replaced bias ply tires with radials on a 1977 C-10 and is what I've used on half-ton 15" wheels ever since.

Sadly, the 1966 C-10 got wrecked by a drunk driver in 1968 and even though the insurance fixed it, my mom traded it off for a new 1969 C-10. But I always liked and missed that pickup. It was long wide bed, white with the chrome strip, 250 straight six and three on the tree. We made a couple summer camping vacations to Colorado in it.