| The gears in the transmission and the differential | | | | a 5-speed transmission if you're driving on a |
| control the acceleration and top speed of a car. A | | | | relatively low-speed track where you never shift |
| gear is identified using its "gear ratio". For instance, | | | | up to fifth gear. In this case, you could install a |
| the first gear in the Nissan 240SX 5-speed | | | | shorter final gear, which will have the effect of |
| transmission has a gear ratio of 3.321:1. This | | | | shrinking the difference between gears and |
| means that (when the transmission is in first gear) | | | | allowing you to use the fifth gear. The opposite |
| the driveshaft rotates one time for every 3.321 | | | | problem is when you run out of gears (reach the |
| rotations of the engine. First gear allows the | | | | RPM limit in fifth gear). To allow for more top |
| engine to operate in the RPM range where it | | | | speed, you can install a taller final gear, which will |
| makes the most power even when the car is | | | | have the effect of increasing the difference |
| moving slowly. This is the purpose of a | | | | between your transmission's gears. Before |
| transmission. | | | | choosing a new final gear, you can use the Top |
| A short gear is one with a low gear ratio, and a | | | | Speed Calculator at to find what the top speed of |
| tall gear is one with a high gear ratio. For example, | | | | your car will be with the new gear ratio. It is also |
| a 3.321:1 gear is shorter than a 1.902:1 gear. | | | | possible to change the individual gears in your |
| In racing, you want to set up your gears so that | | | | transmission, but this is not practical. It is usually |
| you can use the full potential of your engine in | | | | only done by professional race teams. |
| each gear. In other words, it is not useful to have | | | | |