What the ratings mean: torque vs. speed

Servos are usually rated by how long they take, in fractions of a second, to complete a 60-degree sweep without a load and by their torque, which is expressed as oz.-in. Additionally, most manufacturers provide speed and torque ratings at 4.8 volts (for a 4-cell receiver pack) and 6 volts (for a 5-cell pack). Even if a 6V rating isn’t provided, it is usually safe to use a servo at that voltage—unless its manufacturer says otherwise. In general, you should buy the fastest servo with the highest speed and most torque you can afford. Manufacturers frequently sell a servo under two item numbers; the only difference between the two servos is that one is geared for speed and the other is geared for torque. If you have to choose, go for more torque, since all the speed in the world won’t help you if your servo doesn’t have enough torque to turn your vehicle’s wheels.