Define Gearbox Ratio


In short, the ratios of a transmission's gears define its ability to convert engine RPM to acceleration. These ratios play a role in top speed, acceleration, fuel mileage and even engine longevity.


  • A gear ratio is defined as the difference between input shaft (engine) speed, and output shaft (drive-shaft) speed.


  • Transmissions have low first gears that permit the engine to spin faster than the tires, which increases its mechanical advantage and increases acceleration.


  • The gear's "ratio" is the number of teeth on the output-drive gear compared to those on the input shaft. If a transmission has an input shaft with 20 teeth that meshes with a 60-tooth gear on the output shaft, then its ratio is 3 to 1 (60 divided by 20).

Ratio Spread

  • If a transmission has many gears that are very close in ratio, it is called a "close-ratio" transmission. This gear arrangement increases acceleration in vehicles with high-revving engines.


  • An overdrive gear is one that uses a smaller gear on the output shaft than that on the input shaft. This causes the drive-shaft to spin faster than the engine, which increases fuel economy under cruise conditions.

Related Searches


  • Photo Credit Image by, courtesy of Reg Mckenna
Promoted By Zergnet



You May Also Like

  • Define Gearbox

    A gearbox is a collection of mechanical components that deliver maximum power from an engine by managing a series of gear ratios...

  • What Is a Gearbox?

    A gear is a simple device that can change the speed, direction or torque of a motor. Visually, a typical gear looks...

  • How to Calculate Gear Box Ratio

    The gear box ratio is the difference between the RPM produced by the motor and the RPM measured after the gearbox. A...

  • How to Calculate Gear Ratios and Torque

    In the theory of mechanics, torque is a twisting force applied to an object. The force is applied by a lever which...

  • How to Explain Ratios

  • Definition of a Final Drive Ratio

    The final drive ratio is used in the car industry and tells how many rotations your motor must make for each rotation...

  • What Is a Gear Ratio?

    A gear ratio is a generic term that is used to describe the relationship between a drive gear and the gear that...

Related Searches

Check It Out

How To Travel For Free With Reward Points

Is DIY in your DNA? Become part of our maker community.
Submit Your Work!