Rear-End Gear Ratio and How To Calculate It

The rear-end gear ratio is obtained by determining the relationship between two gears: the driven gear (ring) and the drive gear (pinion). To calculate the rear-end gear ratio, you need to divide the driven gear tooth count by the drive gear tooth count. To do this math accurately, you must know the number of teeth the driven and the drive gear. For example, if ring gear has 41 teeth and the pinion gear has 10, then the rear end gear ratio is 4.10:1. This means that whenever the ring gear makes a single rotation, the pinion will make 4.10 rotations.

The rear-end gears can be equated to mechanical levers that offer mechanical leverage for multiplying the torque. Therefore, this facilitates the movement of the power from the engine to the wheels of your truck. Higher the gear ratio provides more leverage to facilitate the acceleration of your mini truck. Such gear ratios are known as the “lower” or “deeper” gears. When the gears ratio drops, the gear set will offer lesser mechanical leverage because it becomes taller. 

This illustration explains how the rear gear end works in a truck. The relationship between these gears is similar to fixing a tire using a socket wrench versus using a long beaker bar. You will use more force when using the small socket wrench (tall gears). Consequently, you also use minimum force when using long beaker bar (deep gears).

Calculating the Rear End Gear Ratio

The drive gear is the first gear attached to the motor shaft, and the driven gear is attached to the load shaft gear. Have the following to calculate a correct gear ratio for your mini truck.

  1. Get the ring and pinion and count the number of teeth each has. You will realize that the two have a different number of teeth. The experts will refer to the one with many teeth as gear while the one with fewer teeth as the pinion.
  2. After obtaining the number of teeth, each has, divide the number of teeth the driven gear has by the number of teeth the drive gear has, for example, 28/21 or 4:3

Low gear ratio is a term used to refer to a high numerical gear ratio. While a lower numerical ratio is referred to as higher gear. The low gears are suitable for small engines because they facilitate faster acceleration. On the other hand, the higher gears are suitable for powerful engines because they cause higher top speed and provide better cruising.

 The above ratio shows that when the driven gear rotates once, the drive gear will rotate 1.3 times.

If you are thinking of changing your gear ratio, think of the factors that impact the gear ratio below.

  1. The torque converter stalls speed.
  2. The type of transmission narrows down each gear ratio.
  3. Your truck’s tire diameter. 


Knowing how to calculate the appropriate gear ratio will help you understand relationship between the driving and the driven gear. This is in terms of the number of teeth each has and rotations they make to generate power for rotations.

Posts Tagged with… ,