<VV> Tires for Greenbrier

[Bruce Schug]

On Oct 14, 2004, at 11:07 PM, Dale Dewald wrote:

> Hello Mike,
>
> It is interesting to note that most modern minivans are OEM'ed with 
> ordinary P-metric non-speed rated passenger car tires.  LT tires are 
> reinforced to withstand higher inflation pressures in order to carry 
> higher loads--but I don't think they have much advantage with regard 
> to stability.  I would suggest looking for a high speed (H, V, W) 
> rated tire which is specifically designed for enhanced stability at 
> highway (and above) speeds.  Often these are reinforced and rated for 
> higher inflation pressures in the interest of stability enhancement 
> rather than load carrying capacity.
>
> Case in point:
>
> On our '65 Greenbrier I have Pirelli P-4000 V-rated P215/65R15 tires 
> mounted on Corvette 15X6 rally wheels (3-1/2" backspacing).  These are 
> the same rev/mile (799) as a P205/75R14 (close to stock 7.00-14 = 
> 185/80D14).  These V-rated tires have a maximum inflation pressure of 
> 51psi.  I usually run 47 front/50 rear.
>
> Dale Dewald
> Hancock, (UP) MI
>

Good grief, Dale, 47/50 psi??? Are you running this all the time or 
just for economy runs? :) Seriously, doesn't it ride like a truck? 
(humor).

The other thing that caught my eye was your reference to tire 
diameters. First, let me say, I don't have an FC. I have no experience 
in fitting wheels and/or tires on FC's. But I do have information 
regarding the original tire sizes of all Corvairs.

Long time VirtualVair readers will remember the "discussions" we've had 
in here on original tire diameters for the 13" Corvair sizes. After, 
literally years of "discussion" even my staunchest adversary has agreed 
that original 7.00-13's were about 25.3" in diameter. This does not 
mean that if you buy a modern radial that is that diameter you'll have 
an accurate speedometer. This has nothing to do with accurate 
speedometers. Corvair speedometers and odometers weren't accurate from 
the factory; they still won't be accurate. If you want speedometer 
accuracy, that's another issue. What I want to address is simply the 
overall diameter of the tires.

6.50-13's that I have a record of were 24.1" to 24.6" in diameter. The 
Coker Classic and US Royal 6.50-13 is 24.58" diameter. These seem to be 
on the large side of 6.50-13's although the Tire and Rim Association 
lists 6.50-13's as 24.7". So we might conclude that 6.50-13's were 
about 24.6" for sort of a "par" value.

So, what about the larger 7.00-14's? Well, if 7.00-13's were 25.3", the 
7.00-14 would logically be 26.3". But Coker's BFG Silvertown 7.00-14 is 
listed as being 26.80" in diameter, a half-inch larger. 
Bridgestone/Firestone reported three different 7.00-14's that were 
25.9", 26.2", and 26.3" in diameter, supporting the theory that the 
7.00-14 ought to be 26.3" But the Tire and Rim Association lists them 
as 26.8". How can they list such a large diameter? Because they show 
the 7.00-13 as being an 86 aspect ratio tire (remember all the talk 
about the Corvair tire being a "low-profile" tire) while the 7.00-14 
has an aspect ratio of 90.

There seems to be an even larger variance in diameters with the 
7.00-14's than with the 13" sizes, making the determination of a "par" 
size even harder. If you believe the 7.00-14 was the same "low-profile" 
tire as the 7.00-13, then the 26.3" diameter makes sense and is 
supported by the Bridgestone/Firestone tires' diameters. If you feel 
that the 7.00-14 was more of a "truck" tire with a higher aspect ratio, 
then the 26.8" dimension is probably a good "design" diameter.

In reality, there were tires that seemed to follow both formats. I tend 
to think that the standard for 7.00-14's was 26.8", as supported by the 
Tire and Rim Assn and the Coker tire. But it looks to me like there 
were tires made of a lower profile that were sort of "Corvair tires" 
that were more like 26.3", as shown in the three Bridgestone/Firestone 
tires.

So, what should be used for a "design" or "par" figure for the 7.00-14 
diameter? I'm open to suggestions.

P.S.

Dale, note that the mathematical diameters of a 205/75-14 and a 
185/80-14 are 26.11" and 25.65" respectively. A 195/80-14 would be 
26.28".

Bruce

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

CORSA member since 1981

'67 Monza. "67AC140"