Speeds and ratios can be figured here
http://www.onlineconversion.com/bigger_tires.htm
0.85 OD ratio is better than none, and in many cases better than faster ones if the rest of the system works out to give you the road speed you like. Having a mild OD like that makes for an easy and often used shift between direct and OD when hills approach, and you can then keep the same road speed but bump the engine RPM up to crest the hill.

Also check parts and prices with Randal at Central Truck and Trailer in Hagerstown 301-797-1995.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-