[TJS2000]

I joined this forum to learn. Can anyone explain the differences between gearing? Like what is a 3.73 and how is that different from other gearings? How does it affect off road capability, gas mileage and I've noticed it comes up when talking about switching to bigger tires. Also how many types are there and why you choose one over another? Thanks.

 

[UnlimitedLJ04]

Ever ride a 18/21-speed bicycle?

3.73 is actually 3.73:1, in other words driveshaft rotations:wheel rotations

the lower the numerically number, the more driveshaft rotations needed to make one wheel rotation.

so 4.88s is said to be "deeper" than 3.73s. As tire diameter increases, the number of rotations per mile decreases because the circumference is larger.

Same idea as a bicycle...when you're pedaling slow up a hill, you use a lower gear...

 

[Jerry Bransford]

Think of different axle ratios like the different ratios in your transmission... like the ratio difference between 1st and 2nd gear.

The axle ratio is chosen based on a lot of factors but on a TJ, the right axle ratio is based on the tire size, engine type, and transmission type. Change any of those and the right axle ratio changes too.

The bigger and heavier the tire, the more HP the engine needs to turn it which means the bigger and heavier the tire, the higher the RPM the engine needs to run at to be able to turn it.

So the RPMs required to turn a 30" tire are lower than what is required to turn a 35" tire. Which is why the goal of regearing is not to simply restore the engine RPMs back to what they were with the smaller factory tire. To properly regear a Jeep, you need to select an axle ratio that will give you slightly higher RPMs for the bigger/heavier tire than what was needed for a smaller lighter tire.

So if you're looking for guidance on a good ratio for new bigger tires, we'll need to know your model year, engine type, transmission type, and tire size.

 

[TJS2000]

Thank you. That makes sense. Now I know what people mean when they refer to 3.73 gears, etc.