Figuring out what gear
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Elder User
Joined: Nov 2003
Posts: 522
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From: Harrisburg, OR
Figuring out what gear
I've got a 292 f100 w/3manual and 295/50/15 tires. I would like to get the right gears. I've looked at alot of different places in the forum and on the net with no luck. The closest thing I came to was a graph that showed the tire size to the gear ratio to the RPMS at 65, but It didn't go down to a 26 inch tire. Can anyone help 
Postmaster
Joined: Dec 2002
Posts: 3,959
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From: USA
26" is a fairly small tire, I would think 3.08 gears would be plenty of gearing with that tire size. You could probably get away with as high as 2.75 and be fine. My '69 Bronco came with 3.50 gears and I think the stock tire size was somewhere around 27" but don't know for sure since all I've ever had on it are 31" tires. Using the formula: RPM = (MPH X GearRatio X 336) / TireSize..., 3.50 gears with a manual trans would give you 2940 rpms @ 65mph, 3.08 gears would give you 2587 rpms @ 65mph and 2.75 gears woud give 2310 rpms @ 65mph.
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Elder User
Joined: Nov 2003
Posts: 522
Likes: 1
From: Harrisburg, OR
Thanks for the formula. I found a third member at a wrecking yard with 3.2 something I don't remember the last digit for $125.oo... It sounds like that will get me in the ball park. Right now I have around 2.55 gears. It's a little slow off the line, like I'm in third gear. I'm going to go with a little bigger tire in the future. I just got the truck and the tires are in great shape. Thats the size all the way around. I'm going to put narrower ones on the front and keep the old ones for spares on the back
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hivoltj
1973 - 1979 F-100 & Larger F-Series Trucks
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Jan 19, 2014 11:14 AM
