Re: 304/290/200R4 - now V8 Fuel Mileage

["Jim Blair" <carnuck@xxxxxxxxxxx>]

A: If anyone wants to swap their Model 20 3.73 or 4.10 gears for the 3.31 
set I have, I'd be glad to do so! (Preferably if they are close to Seattle 
or possibly Nashville later this summer while I'm on vacation)


From: farna@xxxxxxx
Subject: Re: 304/290/200R4 - now V8 Fuel Mileage
To: mail@xxxxxxxxxxxx
Message-ID: <ADVANCES62z2Mb1s7nl0000054e@xxxxxxxxxxxxxxxxxxxxxxx>

A good site for gear/tire calculations: http://www.4lo.com/
That's why I don't have 60 or 65 series tires on my Classic. I think they 
would look better, but would knock me out of the cruising rpm range I want 
to be in. I could drop to 3.31 gears (instead of 3.55) and stay in the same 
range with a 60 series tire instead of a 70 series. That's one reason I 
wanted 3.31 gears -- could use the 65 seriess and gain a few mph at my 
target cruising rpm and look a bit better!

My tire size: 205/70, 15". Diameter (avg.) is 26.3"
              205/65 15 is 25.5" (avg.)

w/3.55 gears and 205/70 tires I'm running ~63 mph @ 2000 rpm.
Drop to 205/65 tires and speed drops to 61.1 mph @ 2000 rpm.
I'd need a 3.44 axle to maintain the same speed, or a 24.5" diameter tire 
w/3.31 gears (205/60-15 is ~24.7", and would be 63.5 mph @ 2000 rpm).

On the 4Lo site don't forget to enter 1 for the transfer case ratio (1:1) 
and enter your high gear ratio. I used 0.70 for the OD gear in the AW4. High 
gear in all three speed autos and most three/four speed manuals is of course 
1:1. You can figure speed in any gear if you know the ratio. I used 
"average" (avg.) and "approximate" (tilde [~] means approximately) for tire 
sizes as there is a little variation among manufacturers. Should be +/- 

about 0.125" though.