FRC Gear Ratios Explained

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.

What a gear ratio actually is

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.

The speed-versus-torque tradeoff

You cannot get both high speed and high torque from the same gearing. Every ratio sits somewhere on that tradeoff:

• A lower reduction (numerically smaller) gives a faster top speed but less pushing force and slower acceleration.
• A higher reduction (numerically larger) gives more torque, better acceleration, and more pushing power, but a lower top speed.

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 L4 ratios, where L1 and L2 are the popular choices for a standard full-weight competition robot.

How to estimate your robot's speed

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:

• Motor free RPM: use the published no-load speed. Common FRC motors are the NEO at about 5820 RPM, the NEO Vortex at about 6784 RPM, the Falcon 500 V2 at about 6489 RPM, and the Kraken X60 at about 6048 RPM at 12 volts (about 5640 RPM with FOC enabled).
• Efficiency factor: real gearboxes lose energy to friction, and a robot never runs at its theoretical max. Most teams multiply by roughly 0.80 to 0.85 to get a realistic number.
• Wheel circumference: that is wheel diameter times pi, converted to feet. A 4 inch wheel is about 1.05 feet around.

For a worked example, take a Kraken X60 at 6048 RPM, a 6.75:1 reduction, and a 4 inch wheel. Theoretical free speed is about 17.5 ft/s; after an 85 percent efficiency factor, you land near 14.9 ft/s, which is a sensible real-world target.

Choosing a ratio for your game

There is no single correct ratio, only the right one for your robot and the year's game. Use these guidelines:

• Heavier robots and games with lots of pushing or defense favor more reduction (more torque).
• Open fields where you sprint between scoring locations favor less reduction (more speed).
• Most competitive swerve drivetrains land somewhere around 15 to 18 ft/s of free speed. REV's default MAXSwerve template, for reference, is set to 4.8 meters per second, which is roughly 15.7 ft/s.
• Do not chase the highest number. A drivetrain you cannot control, or one that browns out the battery under load, will lose matches that a slightly slower, well-tuned robot wins.

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.