How to Determine a Car’s Rear End Ratio

The torque that a car engine supplies to the rear end gear is used either to accelerate or speed up the vehicle. The car’s rear end ratio decides the primary usage of the engine’s torque. For instance, if the rear end ratio of your car is high, it will accelerate much faster but its top speed will be reduced. Similarly, a low rear end ratio will mean that the top speed of your car will be high whereas its rate of acceleration will be low.

Things Required:

– Jack
– Jack stands
– White tire chalk


  • 1

    Raise the vehicle with a jack and support it with jack stands to ensure that the vehicle does not slide of the jack while you are working underneath it. Position at least a couple of stands at the rear axle because you that is where you will be working. Make sure that you take care of this step properly because each year, numerous people get brutally injured by skipping this critical safety precaution.

  • 2

    With a piece of white tire chalk, draw two white marks, one on the tire and one on the ground. Both chalk marks should be in line with each other whereas the mark on the ground should be directly underneath the tire.

  • 3

    When you are done marking the tire and the ground, it comes to marking the driver shaft and the differential. With one hand, hold the wheel that you marked so that it does not move and with the other hand, place white chalk marks on the driver shaft and the differential. Remember that keeping the wheel stationary is very important because you will end up with the wrong results if you let the wheel move at this step.

  • 4

    You can now determine the car’s rear end ratio. Start rotating the wheel in any direction and simultaneously count how many times the driver shaft turn. Use the white chalk marks on the tire, ground, driver shaft and the differential in order to keep track of the number of times the drive shaft turns.

  • 5

    For each revolution of the wheel, calculate how many times the drive shaft turns. This will be the car’s rear end ratio. For example, if the drive shaft turns 4 times for each revolution of the wheel, the rear end ratio will be 4:1.

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