A Jeep Wrangler JK is equally at home on highways as it is off-road, but sometimes the equipment you need may vary. Tires are an obvious item that can be adjusted depending on where you’ll be driving your Jeep, but equally important are the gears in your drivetrain.
What Regearing Means
"Off-road Jeeps may need more torque for rock crawling"
Regearing refers to the process of changing your pinion gears and ring gears to a different ratio, which changes the balance of torque and speed. Regearing your Jeep is a crucial step in adjusting the size of your tires since improper gearing can result in more stress being transferred to the axle. In all likelihood, when you left the lot in your new Jeep, your drivetrain and gearing were set to provide a balance between torque and speed. Balance is great, but highway drivers may discover they want a higher top speed, likewise, off-road Jeeps may need more torque for rock crawling.
Think of it like riding a bike. If you’re climbing a steep hill, you’re going to want a different gear ratio than you will for coasting downhill. A lower gear (referred to as taller) provides for faster speeds and better fuel economy. A higher gear (referred to as shorter) provides adequate space for larger tires and enables rock crawling.
How to Read Gearing
Gear ratios are based on how many rotations your driveshaft needs to complete to turn your wheels once. For a 3.21 gear your driveshaft would turn 3.21 times for every one rotation of your wheel. So, for example, if you have the 4.10 gears and 33-inch tires that come standard on the Rubicon and you are driving at 70 miles per hour, your driveshaft would have to turn 2,426 times per minute. It’s a big number, but it’s perfectly good and reasonable. But if you traded to a 4.88 gear your rotations would increase to 2,773. The engine will have to work a lot harder at highway speeds which will cause a decrease in fuel efficiency. For a daily driver, this would hardly be ideal. But for rock crawling? It’s a great combination!
To go back to our bike example, let’s say you want to climb a hill. You’d change your gearing so that you were pedaling many times for every rotation of the wheel. So, the RPMs lead to a better and easier climb over rough terrain, but as anyone who has ever operated a bike at that kind of gear would tell you—it’s taxing and you’ll have a harder time going at a fast speed.
What Gear Do I Need?
Since regearing is based on a ratio, the first thing you’ll need is the circumference of your tires. Essentially you’ll want to follow a formula that looks like this:
(Old Gear Ratio X New Tire Size)/ Old Tire Size = New Gear Ratio
Then you’ll just need to round up to a standard gear ratio.
In general, you’ll want a ‘taller’ or smaller gear for highway driving and a ‘shorter’ or larger gear for off-roading.
There are a few things to know before regearing. Though regearing is a relatively simple process, doing it incorrectly can mess up your Jeep and your day.
Front and rear axles need to be regeared simultaneously. The Jeep’s transfer case works best when both driveshafts spin at the same speed. A significant difference in speed of driveshafts can cause the transfer case to break, and from there a whole mess of complications can ensue including broken axles, driveshafts, or just wearing out parts long before their time. All of these repairs can be very expensive, and are just unnecessary as long as you adjust your gears all at once.
The hardest part for a lot of Jeep enthusiasts is giving the new gears time to break-in. You’ll want to drive for about 500 miles to break them in. Regearing the weekend before a major off-roading trip is a huge no-no, partially because it’s not uncommon to need to make minor adjustments after regearing. After the break-in period is over, you should change the differential fluid since this will be the period where "new part debris" will be polluting the liquid.
Regearing is an upfront cost that can save you a lot of money and time in the long run by ensuring that your Jeep is running efficiently and that energy is going where you want it to go. Like tires, gears are an investment that will pay you back not only in money saved, but also in the comfort of knowing that your Jeep is ready to perform the way you need it to.