Gear ratio help needed!!!
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New User
Joined: Jan 2003
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From: Colorado U.S.A
Gear ratio help needed!!!
I need help figuring out what’s the best gear ratio to go with in my truck. I have a 1999 Ford F350 PSD with a 14” lift and 44” tires. I currently have 3.73 gears in the front and rear differential. Since I am running 44” tires, it takes allot to turn those big meats, the truck does run a little sluggish! What is the best gear ratio to go with in the front and rear differentials (4.56 or 4.88)? The truck is a daily driver and I do travel the highway frequently. I’ve had one shop here in Colorado tell me that I can only put 4.56 in the front differential and not 4.88’s. Then I had another shop tell me that I can run 4.88s in the front, so now I’m confused
Posting Guru
Joined: Oct 2001
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From: Oxnard, CA
Gear ratio help needed!!!
acording to randy's ring and pinion:
5.38s will put you about 60 RPM higher than stock.
you can also check what is available there (some other companies may have different ratios avaliable tho and that is prob why one place tells you one thing and another something else).
i assume you have a dana 60 in front and a sterling 10.25 in the rear.
5.38s will put you about 60 RPM higher than stock.
you can also check what is available there (some other companies may have different ratios avaliable tho and that is prob why one place tells you one thing and another something else).
i assume you have a dana 60 in front and a sterling 10.25 in the rear.
Last edited by abendx; Jan 27, 2003 at 09:09 PM.
Post Fiend
Joined: Dec 2002
Posts: 6,245
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From: IL, USA
Gear ratio help needed!!!
abendx, your link didn't work, it appears you mispelled pinion.
So try this link to Randy's
Edit: '99 had the Dana 50 front and Sterling (Ford) 10.5" rear.
FWIW, I think the 10.25" and 10.5" use the same carrier, only difference is size of ring gear. Could be wrong.
So try this link to Randy's
Edit: '99 had the Dana 50 front and Sterling (Ford) 10.5" rear.
FWIW, I think the 10.25" and 10.5" use the same carrier, only difference is size of ring gear. Could be wrong.
Last edited by DCSpecial; Jan 27, 2003 at 09:50 PM.
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From: Colorado U.S.A
Gear ratio help needed!!!
DCSpecial you're right, I have the Dana 50 up front and Sterling (Ford) 10.5" in the rear, but then again it might be the 10.25 not too sure either? I've heard that if the rpm's are too high that can cause problems with the engine, is this true? If so, what area should the rpm's be at?
Post Fiend
Joined: Dec 2002
Posts: 6,245
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From: IL, USA
Gear ratio help needed!!!
You don't want the RPM's too high, but as abendx pointed out you'll only push 60 more RPMs than a stock truck. So, your RPMs will be well within the range that is safe for the PSD.
FWIW, I plan to go with 4.56 gears when I upgrade to 38" tires on my PSD.
For work, I drive a F450 ZF-6 with 4.88 gears and the stock tires that are approx. 31-32" tall. Now that is some low gearing to have, especially with the ZF-6. Great power for towing but I push 3000 RPMs around 70 mph in 6th gear.
So with your 44" tires, 5.38 gears will give you only a slight increase (60 RPM) over a stock truck with 31.8" tires and 3.73 gears.
The newer SDs like yours have the 10.5" rear.
Hope this helps.
FWIW, I plan to go with 4.56 gears when I upgrade to 38" tires on my PSD.
For work, I drive a F450 ZF-6 with 4.88 gears and the stock tires that are approx. 31-32" tall. Now that is some low gearing to have, especially with the ZF-6. Great power for towing but I push 3000 RPMs around 70 mph in 6th gear.
So with your 44" tires, 5.38 gears will give you only a slight increase (60 RPM) over a stock truck with 31.8" tires and 3.73 gears.
The newer SDs like yours have the 10.5" rear.
Hope this helps.
Posting Guru
Joined: Oct 2001
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From: Oxnard, CA
Gear ratio help needed!!!
thanks for the link fix DC!
as for the
also, the psd comes witha 4.10 option stock also... so this ratio with the 5.38s is way below that of the stoker running the 4.10s.
as for the
also, the psd comes witha 4.10 option stock also... so this ratio with the 5.38s is way below that of the stoker running the 4.10s.
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From: Colorado U.S.A
Gear ratio help needed!!!
Thanks DC & abendx. It looks like I'll be going with the 5.38's. I looked at the link you posted and ended up talking with the guys over at randy's ring and pinion today and that's what they recommended as well. Thanks for the advice: I'll let you know how it goes.
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Freshman User
Joined: Jan 2004
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From: Ellicott city, MD.
You guys are forgeting an important aspect in this decison. A high ring gear ratio in the back is fine and dandy but that dana 50 up front is not nearly as big. As your ratio gets bigger teeth get smaller. A friend of mine with a toyota pickup with 38" and the stock rear with a set of gears in the lower 5 range all he kept doing was snapping teeth of left and right. He went through three sets before some one told him that those size of tires would shear those little teeth on that ring right off. Thats with a four cylinder toyota. So keep off the gas if thats your route
Freshman User
Joined: Jan 2004
Posts: 32
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From: Ellicott city, MD.
If you really want to be able to use that set up with those high gears I would advise a dana 50 swap to the 2001 SD Dana 60 or the dually fronts. Get one from a salvage yard and save yourself some money since your changing the gears any way.
