Gear reductions, gear reductions, gear reductions. We like to throw them in wherever we can. And why wouldn’t we? Gear reductions 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 and why 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) and put them together. Turning one gear will cause the other gear to turn. Super simple.
If you decide to turn the large gear by hand, you’ll notice a lot of resistance, but the connected small gear make 2 rotations for every one rotation of the large gear. You will gain a bunch of speed (output rpm is 2 times the input rpm) but lose torque. If you decide to turn the small gear by hand, you’ll have almost no resistance, but you’ll have to turn it three times 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 put a wheel and tire on there, 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 but torque helps you keep going.
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 drive train 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 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.
We get the gear reduction in our portals by applying this science (portals have a third gear between the big and little gear. The middle gear’s job is to make sure your wheels turn in the right direction and it doesn’t affect torque. Just FYI.) And obviously the same thing happens in your 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. So check out SuperATV.com to see how you can take some simple physics lessons and turn them into over-the-top off-roading fun.
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