gear ratios
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New User
Joined: Jul 2003
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gear ratios
hi folks. i have a 97 f350 psd srw. don't tow much with it. work truck as well as personal vehicle. wondering if i have the right gear ratio for my needs... it does about 55 at 1800 rpm in overdrive. i'd like to see it go faster at this engine speed. any thoughts? thanks
Senior User
Joined: Apr 2003
Posts: 424
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From: Northern IL
gear ratios
There were only 2 axle ratios offered in 97, 3.70,4.11. From what I have found out there is maybe a max 2mpg dif in the city between the two. Do you have the stock size tires? This will make a difference on rpm at a given speed. I don't drive 55 much but I have 265/85-16 tires (stock size) and I run about 2200 rpm @ 70 mph.
Post Fiend
Joined: Aug 2002
Posts: 5,324
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From: Denton,TX
gear ratios
Originally posted by SHartman
Not true, my 97 has a 3.55 ratio.
Not true, my 97 has a 3.55 ratio.
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New User
Joined: Jul 2003
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gear ratios
thanks for the info. my tire size is 255/85-16. i have to run 2200 ish to do 70. be nice to do 70 down around 1800. seems like a good engine speed for the highway. is there anything i can do?
Postmaster
Joined: Feb 2002
Posts: 2,773
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From: Bonney Lake, WA
gear ratios
It sounds like you've got 4.10's. To drop your rpms significantly, you'd need to get taller tires. Much taller tires. I've got 35's on my truck, which also has 4.10's, and I'm turning 2000rpms @ 69mph. To get down to 1800rpms, you'd have to go to 38's, which probably wouldn't be practical. All of your options are a litlle pricey. You could get an overdrive/underdrive unit, install taller gears in the differential(s), or go to taller tires, with a lift kit, etc. You'd likely never save enough money on fuel to recoup the expense of the mods.
Just try to be content in the fact that you're in a good spot in the powerband for torque, and you can tow a house.
Just try to be content in the fact that you're in a good spot in the powerband for torque, and you can tow a house.
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gear ratios
i hear you quadzilla. so would installing different gears in the differentials be the thing to do?
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Postmaster
Joined: Apr 2001
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From: Baileyton, TN
gear ratios
I need to get taller tires 
Today I checked very carefully and I am getting a hair over 75 at 2000 rpm. That is with 4.10:1 gears, and the aux in high. If I got taller tires the truck would look good, and I would probably get over 19 mpg.. How tall a tire will fit without lifting anything - I can't do any more serious mods to the truck for a while - I just spent a bundle on it, and my wife is only so understanding.
Theo
Today I checked very carefully and I am getting a hair over 75 at 2000 rpm. That is with 4.10:1 gears, and the aux in high. If I got taller tires the truck would look good, and I would probably get over 19 mpg.. How tall a tire will fit without lifting anything - I can't do any more serious mods to the truck for a while - I just spent a bundle on it, and my wife is only so understanding. Theo
Postmaster
Joined: Apr 2001
Posts: 3,628
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From: Baileyton, TN
gear ratios
I have a US Gear overdrive unit - It makes an amazing difference - today I was at 2100 rpm, travelling at 80 mph. with the stock ratio I would up near 3000 rpm at that speed. I do not use the low side of the aux except for really fast take offs (380 hp makes for spinning tires with 4.10 gears.) or for towing in the mountains.
Theo
Theo
