Gear reductions are very cool. It’s no wonder we like to throw them in wherever we can. And why wouldn’t we? They give you more torque—the most coveted of specs for the off-road enthusiast. But what is a gear reduction? Of course you know they get you more torque at the cost of speed, and you probably know that it comes from different gear ratios, but what that means isn’t always clear.
In reality, the way it works is deceptively simple. Here’s how a couple of gears can change the way you ride.
Let’s start with the very basics of a gear reduction. You first need a big gear (let’s say it has 30 teeth) and a little gear (let’s say it has 15 teeth). Now put them together. Turning one gear will cause the other gear to turn. Super simple.
If you decide to turn the larger gear by hand, you’ll notice a lot of resistance, but the connected small gear make two rotations for every one rotation of the large gear. You will gain a bunch of speed (output RPM is two times the input RPM) but lose torque. If you decide to turn the small gear by hand, you’ll have almost no resistance. On the flip side, you’ll have to turn it twice to make the big gear turn just once. You lose speed but gain torque.
Now, speed doesn’t do you much good if you don’t have enough torque. You can spin that gear as fast as you want, but as soon as you hit any resistance, it’ll stop dead. That’s why you mostly see gear reductions that increase your torque and decrease speed. That trade-off is much more favorable because the extra torque will make up for a lot of the lost speed when you’re riding off road. Your speed is compromised by uneven terrain when you’re driving and torque helps you overcome those obstacle so you can reach higher speeds.
But how does using a little gear to turn a big gear get you more torque? That simply has to do with leverage. Everybody’s favorite old dead guy, Archimedes, said, “Give me a long enough lever and I shall move the world,” or something like that (ancient translations are wonky). The point is, the two gears moving together act like two levers trying to move each other. The big gear has a big lever and the small gear has a small lever.
As you know, it’s easier to turn a stubborn nut with a long-handled wrench—and the longer the better. It’s the same thing with gears. Your little gear is turned by a motor in the center and has a lot of leverage against the large gear that is being turned at the edge of the gear. And out pops your bonus torque. Now you’ve got a healthier drivetrain and the ability to run bigger tires.
If you’re still not sure, imagine you have a frozen nut with a breaker bar on it—that’s the big gear and the radius of that gear is the length of the breaker bar. You are the small gear and your radius is the length of your arm. You can turn a much tougher nut in this setup than you could without a breaker bar, but it’ll take a lot longer to unscrew it completely.
Still lost? Here’s one more example. Imagine the sprockets on a bike. When you shift to the smallest sprocket on your pedal and the largest sprocket on your rear wheel, it’s really easy to pedal, but you can’t go very fast. That’s exactly what happens with a gear reduction. Your smaller gear drives your your larger gear, making it easier to go—even if you don’t go quite as fast.
We get the gear reduction in our portal gear lifts by applying this science. (Portals have a third gear between the big and little gear that doesn’t alter torque. The middle gear’s job is to make sure your wheels turn in the right direction. Just FYI.) And obviously, the same thing happens in the standard gear reduction kit that you stick in your transmission.
Gear reductions exist all over your stock machine as well. They’re in your differentials and transmission. But those are just stock. If you’re ready to take your torque to the next level, install a gear reduction to see how you can take some simple physics lessons and turn them into over-the-top off-roading fun.