<VV> Results of Tire Size Request

[Bryan Blackwell]

Bruce,

I matched them by revs/mile.  If you think about it, static diameter  
doesn't really matter to the gearing, revs/mile does.  So, from the  
BFG web site, Traction T/A:

195/60-15 is 860 revs/mile
205/60-15 is 842.

Now, the late speedos are calibrated for 825 revs/mile and the Chevy  
tire spec was 833.  Tire spec for 6.50-13 was 853 revs/mile.  Problem  
is, a bias-ply and a radial don't flex the same, so you don't end up  
with exactly the same diameter tire.  A 205/65-15 would be close in  
diameter at 25.5, but on those wheels I'd be worried they'll hit the  
fenders, and the revs/mile spec is 817.  You could use a 195/65-15 at  
832, which is right on the spec, but it's not an easy to find size  
last I looked, and they are short in diameter as well at 25" even.

Thus, I stand by the 205/60-15 as the best fit for a Corvair with  
7.00-13s and 195/60-15 for cars with 6.50-13s.  The only significant  
difference is visual (especially once you've moved the contact patch  
out an inch), and I don't think most of our calibrated eyeballs are  
good to 1/4" of ride height.  It's not misleading, beyond the fact is  
that the tires today don't measure the same as the ones in the 60's.

--Bryan

On Sep 21, 2009, at 9:11 PM, Bruce Schug wrote:

> I don't think the 195/60-15 and 205/60-15 "correspond" to 6.50-13  
> and 7.00-13's. They may be used instead of them, but the 205/60-15  
> is actually a bit closer in diameter to the 6.50-13 than the  
> 195/60-15 is.
>
> As I tell people, I think the 205/60-15 is a good size tire to run  
> on a 15" wheel, but it is somewhat smaller in diameter.
>
> I think guys can run anything they wish, but I do think it's  
> important to understand how their tires compare to the original  
> sizes as it affects ride height and speedometer/odometer readings.