A beginner-friendly guide to FRC gear ratios and drivetrain gearing: how reduction trades speed for torque, the free-speed formula, and how to pick a ratio.
to read
words
sections
Picking a drivetrain gear ratio is one of the first real engineering decisions a rookie FRC team makes, and it is also one of the most misunderstood. This guide explains what a gear ratio actually does, how to estimate your robot's speed, and how to choose a ratio that fits your game.
A gear ratio describes how a gearbox trades motor speed for torque. When a small gear drives a larger gear, the output spins slower but with more turning force. The ratio is the relationship between input and output teeth. A 12-tooth gear driving an 84-tooth gear gives a 7:1 reduction: the output turns 7 times slower than the input, and produces roughly 7 times the torque (minus friction losses).
That word "reduction" is the key. Drivetrain gearboxes are almost always reductions, because motors spin far too fast to drive wheels directly. A modern FRC motor free-spins at several thousand RPM, and your wheels need to turn at a few hundred RPM. The gearbox bridges that gap.
One naming note that trips people up: WPILib and most simulation tools express the drivetrain gear ratio as output torque over input torque, so a reduction is written as a number greater than 1 (for example, 6.75:1). When you set up a drivetrain model in code, that is the convention to use.
You cannot get both high speed and high torque from the same gearing. Every ratio sits somewhere on that tradeoff:
This is why gearbox vendors like West Coast Products, REV, AndyMark, and Swerve Drive Specialties ship their drive gearboxes with several selectable ratios. REV's 3 inch MAXSwerve module, for example, includes gears for low, medium, and high speed configurations, and an upgrade kit adds even faster ratios. SDS sells the MK4i swerve module in L1 through L3 ratios, where L1 and L2 are the popular choices for a standard full-weight competition robot.
You can predict a drivetrain's free speed (its theoretical top speed with no load) with one formula. In plain terms:
Free speed in feet per second equals motor free RPM, times an efficiency factor, divided by the total gear reduction, times wheel circumference in feet, divided by 60.
A few notes on the inputs:
For a worked example, take a Kraken X60 at 6000 RPM, a 6.75:1 reduction, and a 4 inch wheel. Theoretical free speed is about 15.5 ft/s; after an 85 percent efficiency factor, you land near 13.2 ft/s, which is a sensible real-world target.
There is no single correct ratio, only the right one for your robot and the year's game. Use these guidelines:
The fastest way to sanity-check a choice is a drivetrain calculator. Tools like ReCalc let you plug in your motor, ratio, wheel size, and robot weight to see free speed and current draw before you cut any metal.
For step-by-step help wiring all of this into an actual gearbox and chassis, our Mechanical & Build guide walks through gearbox assembly, wheel selection, and drivetrain layout. If you are still mapping out your whole build season, the full LearnFRC guides library covers the surrounding topics too.
Ready to turn these numbers into a real drivetrain? Start with the Mechanical & Build guide.
This article is AI-assisted: drafted from primary sources, then reviewed and edited by hand. Errors still get through. When one is reported we fix it and write down what changed — publicly, in the corrections log.
Keep going
You came here for one answer. These lessons teach the same subject properly, in the order a team actually learns it. All 47 are free and none of them need an account to read.
Go deeper
This article pairs with a full structured design course — swerve layout, assemblies, worked mini-projects. A free account saves your progress lesson by lesson.
Save my progressKeep reading
Structured lessons and quizzes across every department. Create a free account to save your progress, track your team, and earn a certificate.