<VV> Re:Tirez

Bruce Schug bwschug at charter.net
Thu Oct 20 16:19:08 EDT 2005

On Oct 20, 2005, at 1:56 PM, Padgett wrote:

> Figure Corky Coker's web site is probably going to be pretty accurate. 
> He lists the 6.50x13 as 24.58" diameter

Corky's information, of course is correct, for those particular 6.50-13 
tires. Other 6.50-13's that I have information on range from 
24.1-24.6". The Tire and Rim Assn actually speced the tire at 24.7 - 
but that is just a spec - there's no reason to believe any 6.50's were 
actually that big - but they probably were. Taking everything into 
account I have come up with a "par" figure of 24.5". As you can see, 
actual tires were produced larger and smaller than that, but I feel 
that's a good figure to use as a guideline.

> and a 7.00x13 (actually extrapolating from 7.00x14) 25.80".

Your reasoning is good, but your results are not accurate. The 7.00-14 
is a strange bird. It does not follow the logic of the 6.50 and 
7.00-13's in actual dimensions. Again, after studying the different 
actual diameters of 7.00-13's, which ranged from 25.1 - 25.4 for the 
four tires I have figures for, I have concluded a par figure of 25.3" 
in diameter for the 7.00-13. If you'd rather use fractions, use 25 1/4. 
Again, the Tire and Rim Assn figure for the 7.00-13 is 25.2".

> Am really dredging now but there were a bunch of oddball sizes that 
> had some indication of the profile. Think .00 meant a full profile,  
> .50 or .70 (e.g. 6.70x15 Corvette) meant a low profile (90 ?) and a 
> .x5 (e.g. 7.35x14) meant 80.
> This would explain why a 7.00x13 would have been more than an inch 
> taller than a 6.50x13. Would someone who knows for sure please speak 
> up. I used to have a "Tire Guide" from about 1978 that explained it 
> all but have not seen for a few years.

I'm not sure what you're looking for here. I don't know what the ".70" 
in 6.70 meant. I thought it was section width. I don't think it is the 
aspect ratio, which I think you're calling profile. I can tell you that 
the Tire and Rim Assn specs the 6.50-13 as having an aspect ratio of 
87, the 7.00-13 of 86, and the 7.00-14 of 90. The dimensions I have for 
actual tires does not list the aspect ratio.

Here's a little exercise for you, though. You can compute the actual 
aspect ratio of the actual tires. The section widths and diameters for 
6.50-13's were:
6.72 - 24.4
6.92 - 24.6
6.49 - 24.3
6.63 - 24.4
7.24 - 24.1
6.78 - 24.5
6.96 - 24.4
6.99 - 24.6

For actual 7.00-13's the figures are:
6.99 - 25.1
7.26 - 25.4
7.27 - 25.3
7.20 - 25.1

For actual 7.0-14's the figures are:
6.87 - 25.9
7.05 - 26.2
7.08 - 26.3

Quite a lot of variance, huh? To make matters worse the rim width for 
all of these was 5.0"!!!

Here's another figure of interest, especially to Bill who is trying to 
figure hub to wheel opening figures. The static loaded radius for the 
6.50-13's ranged from 11.1 - 11.5. For 7.00-13's; 11.5 - 11.9 and for 
7.00-14's 12.1 - 12.2.

Another interesting tidbit you may have noticed is that the largest 
6.50-13's (6.99 section width and 11.5 loaded radius) were as large as 
the smallest 7.00-13's (6.99 and 11.5) !!! I will point out, however 
that those figures weren't all on the same tires. But you can see there 
was quite a bit of variance.

And the 7.00-14? As mentioned above Corky's repro is 26.8". The tires I 
have information on were 25.9, 26.2, and 26.3 diameter. The Tire and 
Rim Assn spec was 26.8". Still haven't figured that one out although we 
think it may have something to do with the ply ratings.

> Some charts can be found at http://www.tireguides.com/tip6.html . Keep 
> in mind that a 175x13 is taller than a P175/80R13.

Regarding these kind of "guides", I feel they are almost useless. They 
seem to use load ratings to equate sizes. If you study their 
"recommendations" you will find there is no equality in actual tire 

> You really need a scorecard, it is confusing.

Yup! Study it for years, like I have, and you'll understand it a little 


Bruce W. Schug
CORSA South Carolina
Greenville, SC
bwschug at charter.net

CORSA member since 1981

'67 Monza. "67AC140"

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