I have gotten alot of different answers on this question, so I figured I'd ask you guys.

I just put a 6" Pro-Comp Stage 2 on my 87 Bronco. I'm going with 36x12.50 Swampers and want to know what gear ratio i should put in.

Any help would be great. Thanks for reading.

 

3.73 is the highest ratio you want
4:10 would be the better.

 

(3.55 * 36") / 29" = 4.406

so 4.56 or 4.10, or 4.30 if you can get those gears for both front & rear. It also depends on if you drive a lot on freeways, or tow instead.

 

You can afford to go a little taller and not sacrifice as much mileage IF you have an OD transmission in there. So, 4.56's would give you a bit more low end "umph" but would KILL you on the highways UNLESS you have an OD tranny.

 

man your smoken crack. you would be wasting money putting those gear ratios with that size tire.


if you have an od i would strongly suggest 4.88's it would put you around 2500rpms on the hwy at 70 which is a good running rpm. offroad it would be even better. 4.56 if you dont have od which you would be running probably 2800rpms at that same spead

 

you think that 36s should have a higher ratio than 3.73? because thats what I said. Do you even understand how gear ratios work?

 

have you ever driven a rig with a tire that big? there are charts online that show what ratio you should be running in relation to tire size. i obviously know more then you because 3.55 is stock and 3.73 is hardly an increase. the general rule of thumb is 4.10's for 33's and 4.56 for 35's. you also have to figure the increased weight of the tires as well. plus its better to drive in your motors power range or just below.

 

Man they must have changed the gears in 89, cause on the tag from rear dif i have 3.08s. I am going to be regearing my Bronc as well and I'm pretty sure Kemical is right with going for the big gears. I run 33's now, but I plan on going to 35's so I am investing in some 4.88's. Maybe you guys are confused when Old was talking about high maybe he meant numbers.

 

I meant high ratio, not numbers. Sorry.

 

3.08 was an option , your tranny must be a c6 then bryang.

if you plan to tow and wheel going a little taller wont hurt especially if the tire is heavy which most tires 35" + are. a set of 36" swampers are almost 90lbs a peiec. thats alot of weight to be moven

 

So it would be a good idea to go with the 5.13 if you run 35+?

 

5.13's would be necessary if your running 38's or higher. you could if its a trail only rig and your doing more rock crawling type wheelin. but for mudding and stuff that would be a little to low for 35's.

 

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The Gearhead on Gears and Gas Mileage
January 2005 Gearhead’s “Thirsty Bronco” inspired a boatload of questions that involved the effect of gearing and big tires on fuel economy. Chris had combined 3.55 gears with 35-inch tires on his 1995 Bronco, and his mileage had dropped to eight mpg. First, big tires and lifts will cost mileage. Period! No way out of that-but putting big tires and a lift with the stock gears often costs more mileage as well as a loss of performance. Taller tires feel just like changing to taller gear ratios. Your rig will think it has 2.84 gears with the 3.55/35’s combo. Around town, it will grunt at stoplights like an old man climbing out of an easy chair, and, depending on the tire/ratio mismatch, it may not be able to use overdrive on the freeway and will grunt on any hill steeper than a speedbump. Grunting equals poor fuel economy and poor performance. There are two useful formulae here: equivalent ratio and effective ratio. Equivalent ratio formula puts your overall gear ratio back to the same place it was with the stock tires.

Equivalent Ratio =
(New Tire Diameter/Old Tire Diameter) x Original Gear Ratio

Plug in Chris’ numbers:

(35/28) x 3.55 = 4.4375

Matching that up to the closest available ratio equals 4.56:1. The effective ratio below tells you the overall ratio of the new tire and gear combo, and it’s similar to the equivalent ratio formula.

Effective Ratio =
(Old Time Diameter/New Tire Diameter) x Original Ratio

Again, plug in Chris’ numbers:

(28/35) x 3.55 = 2.84

We can make this easy by following a few rules of thumb: Rigs with 31-inch tires should have 3.73 gears. Rigs with 33-inch tires should have 4.10s. Rigs with 35-inch tires need 4.56s, 37s and 38s need 4.88s, 39-40-inchers need 5.13, and 44s need ratios around 6.0:1. You can fine-tune even closer by using the formulas if your rig’s performance, with stock tires and gears, made you happy.