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!!