Gearing! The chain (or whatever) going from the engine to the wheels or axle of your kart is the only form of drive train a kart has, and the # of teeth on each sprocket (or diameter of pulley or # of teeth on gears) is the gearing of your kart.

Gear reduction multiplies torque by decreasing rpm. Torque is measured in ft pounds. If the wheel was mounted right to the shaft of the engine, or turned at the same speed as the engine, theoretically the machine would be able to go over 200 MPH. But a 5 hp engine for example has 6-8 ft pounds of torque max. This means that the force turning the wheel would be the same as if there was a 1-ft lever coming from the center of the wheel and there was 6 pounds pushing on the end of it. (See Diagram)

You can imagine that if you set your go-kart on level ground, got in it and set a six pound weight on the end of this lever it might move forward, but most likely there will be a little pebble in front of one wheel that would stop the puny power. On the other hand, if the kart had 7:1 gear reduction between the engine and the wheel the power would be 7 times greater.

Now imagine putting a 42 pound weight on the end of that lever, your kart would definitely get going, sadly, your Kart would have a top speed of only 28 mph, so you must find something in between these two extremes. If the engine were really powerful than it wouldn't be important, but most go-karts don't get over 10 HP (about 12 ftpounds).

The speed a go-kart can go is a result of gearing. Also the size of the tires affects the overall speed of the go-kart. I think a go-kart should reach top speed in 8-12 seconds. To achieve this acceleration one must gear the machine for a reasonable top speed. The more engine power you have the higher you can go. For a 3 hp Briggs or less, gear a kart to go 25 MPH. For a Kart Powered by a healthy Briggs 5, gear it to go 35 MPH. A Tecumseh or Honda 5.5 can be geared for forty, 8 hp can take you to 50. More than 8 HP is a serious Kart! If you gear beyond these suggested speeds the Kart becomes faster, but acceleration is to slow to have any fun. Off Road Karts can be geared 10 MPH under these suggestions, and on-road machines 10 MPH over if you want. It all depends on how and where you drive. The size of the driven sprocket will exceed the size of the wheel if you gear too low, !!Careful!!

If you are someone who wants to climb hills Offroad, and then cruise home at 50 on your minibike or go-kart and happens to have $200 of surplus cash in your pocket, there is a solution! Transmissions. These devices allow you to change gear ratios while in motion, or even automatically, just like in a car.

The most common type of transmission for a go-kart or minibike or go-kart is the Torque-a-Verter by Comet Industries. This system uses a weird looking belt and variable pulleys to create additional reduction of 3 in its lowest settings and .8 at its highest range.

This means that the usual chain or pulley (whatever) ratio is multiplied by 3 for low speeds, and .8 for high speeds. These units work well at low speeds, but at high speed, squeezing that big belt around takes a lot of power, so they aren't very efficient. Before the Torque-a-Verter, there was the symmetrical Torque converter, which uses a standard V-belt, it only has a range of 2.5 to 1 reduction, but the smaller belt makes it more efficient.