Gear Ratio

walkdawg · Apr 29, 2004

I am new to the 4wheeling world I have a 89 Bronco with 31" tires. I am about to put on 33" tires. I dont really want to lose my current gas mileage. I here if i change my gear patio it will help is this true? I also was wanting to know just how to tell my current gear ratio.

4xfan78 · Apr 29, 2004

Not real sure on an 89 but most ford rearends have an ID tag near the pumpkin it will have the axle size,gear ratio,and if its a limited slip or open differential. If you have a gear ratio of 3.50 or close to it you should be ok with 33's. It wont have the launch that you would get wit 4.11 but 3.50 will help get better gas milage, and help it run cooler(engine will turn less RMP).

walkdawg · Apr 29, 2004

Thanks I will look and see what I have.

Justshootme84 · Apr 30, 2004

Right, look for a metal ID tag on either axle pumpkin. If you don't know what the numbers mean, just post them and someone will decode them. The 89 Bronco commonly has a 3.55:1 gear ratio ,so going from 31" to 33" tall tires will not make much difference. If you know what the transmission and transfer case are, you can compute the final drive ratio for any size tire. You should have a E4OD tranny and B-W 1356 t-case. Your mileage may even increase with 33"'s, but you may have some minimal power loss. Changing tire height just changes the engine's peak power band, and a gear swap corrects that. It's usually only neeeded when a drastic change is made in tire height, like going from 31''s to 38"'s.

mansquirt86 · Apr 30, 2004

i myself have an 88 bronco. When i first got it, it had the stock 31's on it still and i later went up to the 33's. After doing so you definately notice its not as "fast" (in bronco terms) as it used to be. As for mileage, i didnt really notice too much of a change. The place you notice the difference is off road, that extra rubber sure does help.

Justshootme84 · Apr 30, 2004

Good point, your 1/4 mile time may go from 19 seconds to 20 seconds. Bronco terms!!!

walkdawg · Apr 30, 2004

Thank you all. I will take a look at the ID plate and see what i have.

walkdawg · Apr 30, 2004

I got a chance to get a good look at everything. It looks as if I have 3.55 rear and 3.51 front. after getting the codes and going to www.broncodata.com that is what I have come up with. Thank to you all for your help.

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Seabronc · May 23, 2004

You can find a real neat power vs milage chart, for selecting gears and tires, at the Bronco Graveyard site. Look for the 80 and above parts catalog. the chart is near the end of the catalog. also don't forget you will need to change the speedo gear to get acurate speed and milage indications on your odometer.

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walkdawg · May 23, 2004

Thanks I have put the tires on been running them a week now and the gas mileage has not changed at all it seems and I really need a tune up and I am getting from 11to 13 mpg matters if I get on it or not. I posted pics in my gallery. Here is a pic.