It is not the loaded radius that will give the revs/mile, but the tire
circumference. Measure with a tape measure. As a tire wears, the
circumference will change slightly increasing the revs/mile as the
thread is reduced.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Shawn Wright
Sent: Monday, March 21, 2005 11:32 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Tire trivia

An interesting bit of trivia for this tired of the usual "tire" thread:

I swapped my BFG A/T KOs from my '88 to '82 Westies in preparation for
possible snow on our trip this week. I decided to measure the loaded
radius of each of the tires I have on the ground:

Michelin XC LT4 195/7R14: 11.75" = 858 revs/mile
Yoko Y370 195/7R14: 11.75" = 858 revs/mile
BFG AT KO 27x8.5R14 = 12.625" = 799 revs/mile

The two spares I have in 185R14 OEM size are somewhere in between the
above, but are not on the van.

Since the speedo spec says 805 revs/mile (or 500 revs/km metric), this
means the BFGs are actually much closer to this figure that the
195/75R14
size, contrary to popular wisdom. Interesting trivia perhaps, or maybe
I've
just made an error somewhere?

In any case, this might yield me 4mph at the same revs in my '82 Diesel
:-)
...or it could mean more time spent in 3rd :-(

Road trip time! Back in a week or so... :-)Shawn Wright
http://zuiko.sls.bc.ca/~swright
'85 Jetta TD (retired)
'85 Jetta D
'88 Westy 2.1L
'82 Diesel Westy