how much do gears affect economy?
Thread Starter
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Fleet Mechanic
Joined: Dec 2004
Posts: 1,365
Likes: 6
From: Ketchikan, AK.
how much do gears affect economy?
hi, i have a 99 f250 sd with the 5.4L. i want to lift it up, but i also want to change the gears. now i have the stock 3.73, and want to go to either 4.56 or 4.88. well, i live in alaska, so i will have about a 1,000 mile trip to get to seattle washington. (anyone know a good shop to have the gears switched there??). so, my question is...... how bad do you think my gas mileage will drop on the return 1,000 mile trip with the stock tires and new gears? the average speed of the trip will be 60-70 mph. i am going to do the lift myself once back home, and don't want to put that many miles on a fresh set of tires that fast. i have the stock tires of 265 75 16. also, since i want to go to 37" tires with the lift, which ratio would keep my speedometer closest, and fuel economy the closest? it is an every day driver in a small town average speed of 30 with lots of short but steep hills. thanks in advance !!!
Postmaster
Joined: Nov 2001
Posts: 4,742
Likes: 8
From: OK
If my math is correct, 4.30 gears would put you back nearest the 3.73 ratio once you get the new tires on. I'd probably go with the 4.56 though.
Before heading back to AK after the gear swap, ask the shop about the break-in procedure for the gears... then plan your trip accordingly. Often, a full cool-down is required after the first 25 miles and a gear oil change is required after 500 miles.
Before heading back to AK after the gear swap, ask the shop about the break-in procedure for the gears... then plan your trip accordingly. Often, a full cool-down is required after the first 25 miles and a gear oil change is required after 500 miles.
Post Fiend
Joined: Dec 2002
Posts: 6,245
Likes: 1
From: IL, USA
I agree with NoMo about 4.30s and 37s being about the same effective ratio as stock tires with 3.73s, and to be sure to follow the break in procedure they give you. And that being a gasser most people like going to a lower (numerically higher) gear and would opt for 4.56s or 4.88s.
As far as your speedometer, gears will not effect the reading on the speedometer.....only tire size will. So when you put bigger tires on you'll need to recalibrate your speedometer. I used the Superlift Truspeed module on my SD to recalibrate the speedo.....and I think I remember reading some (if not all) of the gassers can be recalibrate with the use of certain programmers.
And as far as a shop in WA, I know Randy's Ring and Pinion is located in WA....they sell a lot of gears, limited slip, lockers, etc.. Their site is www.ringpinion.com
As far as your speedometer, gears will not effect the reading on the speedometer.....only tire size will. So when you put bigger tires on you'll need to recalibrate your speedometer. I used the Superlift Truspeed module on my SD to recalibrate the speedo.....and I think I remember reading some (if not all) of the gassers can be recalibrate with the use of certain programmers.
And as far as a shop in WA, I know Randy's Ring and Pinion is located in WA....they sell a lot of gears, limited slip, lockers, etc.. Their site is www.ringpinion.com
Thread Starter
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Fleet Mechanic
Joined: Dec 2004
Posts: 1,365
Likes: 6
From: Ketchikan, AK.
wow, thanks a ton for the information NOMO and DC !!! i was not aware about the break-in procedure. i will be sure to ask. I will also look around for a scanner to re-calibrate the speedo. THANK YOU !!!!
