Gear Ratio Solver
The speed calculator backwards. Name a speed you want and get every real VEX gear pair that gets close, ranked by how close.
Inputs
Free speed, as reported by the Drivetrain Speed calculator.
Diameter across the wheel. Mecanum and flex wheels share a diameter with the plain ones, so pick by name rather than by size. Anything not listed can be typed in.
Leave on Any to see what every cartridge could do.
Results
Closest achievable
—ft/s
Using
—
Off your target by
—ft/s
Gear ratio
—
Combinations checked
—
Every option, closest first
| Cartridge | Motor gear | Wheel gear | Ratio | Speed | Off by |
|---|
How this is calculated
There is no clever algorithm here. VEX makes four spur gear sizes and three cartridges, so there are only 147 possible combinations, few enough to work out every one and sort them:
speed = cartridge RPM × (motor gear ÷ wheel gear) × π × wheel diameter ÷ 720With your numbers
Identical ratios built from different gears are collapsed into one row. A 36:36 pair and a 60:60 pair produce exactly the same drive, so only the lighter option is shown.
Why a small list is good news
Working forwards, teams tend to pick a ratio and accept whatever speed falls out. Working backwards shows something more useful: the achievable speeds are a short, discrete list, and your target almost certainly does not sit exactly on it.
That reframes the decision honestly. You are not choosing a speed, you are choosing which of a handful of real options to accept. If none is near your target, the answer is a different wheel size rather than a different ratio.
Sources & assumptions
Gear tooth counts, cartridge speeds and wheel diameters are all VEX published figures. Only VEX's four spur gear sizes are considered, in a single stage.
Speeds are free-running and take no account of load, acceleration or drivetrain losses, so every row is optimistic by the same margin, which makes them fair to compare against each other, and optimistic to compare against a stopwatch.
Compound gearing (two stages) would reach ratios not listed here, at the cost of more parts and more friction. Run each stage through the Gear Ratio calculator and multiply.
- VEX Robotics — Gears — checked 2026-08-17
- VEX Robotics — V5 Smart Motor & Gear Cartridges (276-4840) — checked 2026-08-17
- VEX Library — Understanding VEX V5 Wheels — checked 2026-08-17
Save this run, and compare
Keeps what is on screen so you can change something and see both sides of the change. Saved in this browser only, never uploaded.
Save this as evidence
Collects what you entered, what came out, how it was worked out, and anything the tool flagged, with a timestamp and a version so someone else can reproduce it.
This is evidence, not a notebook entry. It deliberately does not write your problem statement, your reasoning, or your conclusion, because under RECF rules an Engineering Notebook has to be the students' own work and no tool may generate or organise its content. Take the numbers, decide what matters, and write it yourself.