C2 7.75x15 tire Outside Diameter

[David D.]

What is the proper outside diameter for the 7.75x15? Is the Coker Firestone Deluxe Champion at 27.36 inches about right? I need a spare for my driver 66 now that I have a good rim.

[Michael J.]

Re: C2 7.75x15 tire Outside Diameter

I use the Goodyear Power Cushions here:

http://www.kelseytire.com/pages/preformancetires2.html

And they are 26.27", so yes about right I think, but the Cokers seem a little tall..

[Loren L.]

Re: C2 7.75x15 tire Outside Diameter

Dave, the notes I have on the never-on-the-ground Firestone Deluxe Champion spare out of '65 #21083 indicate that it was just a touch over 27" - of course the DA doing the measuring never managed to check the air pressure......

[Duke W.]

Re: C2 7.75x15 tire Outside Diameter

From my library of vintage tires catalogs, the nominal inflated OD of the 7.75-15 is 27.0" and the loaded revs per mile spec is 775. There is some slight variation depending on manufacturer and model, but dimensions for all tire sizes are specified by the Tire and Rim Association, an industry trade organization, to be within a very narrow range.

Modern reproductions of vintage sizes tend to have greater OD, which also means that the revs per mile figure is probably a little lower. I recall that John Hinckley has stated that this is because modern manufacturing standards require the tire to be inflated shortly after it comes out of the mold while it is still hot, which was not the case back in the sixties.

This causes the tire to stretch - up to about an inch of OD - so if the tire is vulcanized in an original mold, it will be larger than when the size was originally manufactured for original equipment.

Duke

[Harry S.]

Re: C2 7.75x15 tire Outside Diameter

I just went down stairs and measured a 7.75 x 15 non-dot General Jet mounted on a rim with 25 pounds of pressure and it's 27.25 inches.

I don't know what it is suppose to be but that is what I get.

Cheers

[David L.]

Re: C2 7.75x15 tire Outside Diameter

I have a NOS Goodyear "ALL WEATHER IV" nylon cord 4 Ply tubeless tire with a DOT stamping of "CCNHJYK9". This tire was NOT original equipment on a 1966 Corvette but I use it for my spare. The circumference measures 85 5/8". The diameter would calculate to 27 1/4".

Dave