Running Gears
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Freshman User
Joined: Feb 2004
Posts: 42
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From: Connell Wa
Running Gears
I have a 92 F-250 with 5.8L and a 5 speed. I just put on 35s and it has 4.10 gears....they arent enough. I need to gear it down and i dont knwo how low to go. I dont want to go 55 down the freeway but i dont liek being underpowered. Does anyone have any sugestions? 4.56, 4.89, 5.23s? i cant decided.
Laughing Gas
Joined: Jul 2003
Posts: 893
Likes: 8
From: Lincoln, Nebraska
i would think your 4.10 would be enough but i wouldnt go lower then 4.56 if you want to run 70 or faster down the freeway know if you are going 65 you will be running 2021 rpms in 5th gear if you are running 75 2332 rpms in 5th. if you go with 4.56 2350 rpm at 65 and 2600 rpm and 75. yea you will have more power but think about milage and your engine if you do a lot of freeway driving and at $2/gallon gas i would definately stay with the 4.10 you should still have good power with that 351.
Senior User
Joined: Jun 2004
Posts: 291
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What size tires did you have before. If you divide the old diameter by the new diameter and divide your current gear ratio by the product of the tire difference ratio you'll get close.
For example:
If you had 29" tires
divide 29/35 = 0.82857.... say .83
now divide 4.10/.83 and you get about 4.94
I don't know enough about axles and gears to know if you can get that exact ratio but I'd pick the next lowest available ratio for that little extra torque to turn the oversize tires over. You should'nt lose too much of your top speed.
If this is wrong anybody feel free to correct me as that's how I plan on figuring new gears in mine. I've got 33" with 3.55 gears. It's sluggish but not a total dog. I'm more interested in taking some strain off the drivetrain. 4.11 should do ok for me. A little low geared w/ 33's and if I decide to put some 35's on, a little tall geared.
For example:
If you had 29" tires
divide 29/35 = 0.82857.... say .83
now divide 4.10/.83 and you get about 4.94
I don't know enough about axles and gears to know if you can get that exact ratio but I'd pick the next lowest available ratio for that little extra torque to turn the oversize tires over. You should'nt lose too much of your top speed.
If this is wrong anybody feel free to correct me as that's how I plan on figuring new gears in mine. I've got 33" with 3.55 gears. It's sluggish but not a total dog. I'm more interested in taking some strain off the drivetrain. 4.11 should do ok for me. A little low geared w/ 33's and if I decide to put some 35's on, a little tall geared.
Last edited by Lumpy87; Oct 7, 2004 at 05:40 PM.
Laughing Gas
Joined: Jul 2003
Posts: 893
Likes: 8
From: Lincoln, Nebraska
a guy on here gave this site that will figure everything for you http://www.4lo.com/4LoCalc.htm
Laughing Gas
Joined: Jul 2003
Posts: 893
Likes: 8
From: Lincoln, Nebraska
you will have to search the web for your transmission ratio but i think yours is going to by .79 in 5th that is what i found and the trans case ratio is 1 it will always be 1 in a stock vehicle in 2hi or 4hi 4lo you will have to find what transfer case you have
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Senior User
Joined: Jun 2004
Posts: 291
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Looks like I was in the ballpark. I like the speedo conversion. I'm not near as far off as I thought.
57 mph = about 65mph for me.
57 mph = about 65mph for me.
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