Gear Change

mansquirt86 · Jun 4, 2004

Ive got an 88 bronco with a 302 and an AOD trans. I want to change from 3.55 gear ratio to most likely 4.10's. My question is what will that do to my gas mileage, improve it or make it the beast even more thirsty? If it helps, i have 33's stuffed on there.
thanks guys,
steve

freak · Jun 4, 2004

It shouldn't really be that bad since you have overdrive.

4xfan78 · Jun 4, 2004

It will not improve it, it may make it worse ( slight difference) because you will be running higher rpm's even with overdrive.

sweepersrgr8 · Jun 4, 2004

BIG BRONCO.COM has a chart, but I couldn't find it. Most 4x4 shops will be able to tell you what gear will keep you in the desired RPM range, with the tires you are running.

Broncoholics · Jun 4, 2004

Stock gears will help gas milage on the freeway but will be reduced in town as it takes alot of juice to get the truck going.
With gears on the freeway you will loose gas as the RPM's are high. In town the gas should improve as its easier to get going and up to speed. :wacko:

mansquirt86 · Jun 4, 2004

alright, thats not too bad i suppose. When i change the gears in the rear, i have to change the front as well correct? Pretty sure that you have to, but i just woke up so the brain hasnt really been warmed up yet.

sweepersrgr8 · Jun 4, 2004

YEP...Front and rear.

freak · Jun 4, 2004

I went from 3.55 and P265's to 4.56 to 35's in my 98F-150 and the gas consumption isn't as bad as I thought it would be.

STLKIKN · Jun 5, 2004

At worst, I think you will find that with the 33's and 4.10s, the truck will behave more like it did stock with 3.55s and ~28" tall tires...
check this chart for comparisons....

(edit) please note that this chart uses a 1:1 trans ratio, multiply the rpm by ~.80 to get an OD ratio... that would put 4.11/33 at 2720 rpm x .80 od= 2176 rpm, that would also put 3.55s at ~ 1800 rpm in od)

Tire size gear comparison...

Seabronc · Jun 5, 2004

There is also a chart in the 80 and above Broncos catalog on Jeff's Bronco Graveyard showing tire size vs gear ratio to select the RPM range you want your engine to run at. According to their chart, at 65 with 4.10 you would be running in the higher end where power is better. Also, according to their chart at 65 you would be running in the best milage range of RPM with 3.55's. So the result according to Jeff's chart is that at 65 you would be better off with your existing gear ratio. Best gas milage being around 2100 RPM.

Good luck,

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