<VV> Re: Tirez

Padgett pp2 at 6007.us
Thu Oct 20 10:30:16 EDT 2005

>I can say with confidence that a typical, properly sized
>and manufactured 185/80-13 tire is very close to the diameter of an
>original Corvair 6.50-13 tire.

Interesting and do not doubt it is true just my notion that "low profile" 
meant an 80 ratio was incorrect and it is more like a 90. So in modern 
tirespeak an 6.50x13 would be a  165/90B13 and a 7.00x13 would be a 178/90B13.

There have been many changes in tire sizes since the '60s. Then the 
Michelin "X" was expressed in metric sizes such as 185x13 which is quite 
different from P185/80R13. Profiles began with the sporty 70 series around 
1966 and with them we got the letter series ranging from "A" (about a 165) 
to L (about a 235). I always thought it odd that the 1967 Mustang used a 
F70x14 while the Z-28 received an E70/15.

Letter sizes lasted until the '80s when they were replaced by the current 
P-metrics (which in general are slightly smaller than a '60s metric size). 
"Replaced" is probably the wrong term because it was not sudden, both size 
types existed size by side for many years. Nowadays I use tirerack.com a 
lot because they list all of the tire specifications which includes 
diameter and revs per mile (which is not quite the same thing and related 
to loaded wheel diameter). Tirerack is also good in indicating the 
recommended rim width for a tire (and I prefer the wider rims).

So there are a lot of potential answers though I agree with Bruce, over a 
half inch difference in diameter between tires of the same size would be 
unusual. Back when "wide boots" were the rage I used to see a lot of 
difference in tread width but not diameter.


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