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.
