<VV> Tire Conversion

Bruce Schug bwschug@charter.net
Thu, 27 May 2004 21:00:55 -0400

These tire size converters or calculators are pretty cool. This one and 
the one Bill Hubble posted. A couple of things to be aware of. They are 
figuring the dimensions mathematically. This is great, but remember to 
check the actual dimensions of the tires you're looking at in the 
manufacturer's literature (or the TireRack web site). They will 
probably be a little different.

Secondly, the revs per mile displayed by these converters appears to 
assume the tires keep their diameter when loaded and turning. Obviously 
this is not true. This is where the "loaded diameter" (twice the loaded 
radius) comes in. For instance, this calculator shows a 225/50-16 to be 
the correct diameter, 24.9". But it shows the rpm to be 811 revs per 
mile. My Goodyear specs shows this tire to have 840 rpm - quite a 
difference. What this means is that you can't use these rpm figures for 
anything, like trying to get tires that match your Corvair's 
speedometer calibration. The calculators are great for diameters and 
comparisons, but just forget the rpm figures except for comparisons to 
other tires. Since these figures are directly proportional to the 
diameters, I'd simply use the diameters for comparisons.


On May 27, 2004, at 4:48 PM, Jim McLott wrote:

> Check out http://www.powerdog.com/tiresize.cgi
> Over the years, I've culled a number of useful web sites from the 
> postings of this list, so I'm happy to have the opportunity to share 
> this one.  I got it a couple of years ago and wish I could remember 
> who first poted it so I could give credit where credit is due.
> hth,
> Jim McLott & Christine, the 1966 Monza convertible she-devil
> Member: CORSA, Corvair Atlanta and Group Red

Bruce W, Schug
CORSA South Carolina
Greenville, SC

CORSA member since 1981

'67 Monza. "67AC140"