Gear Ratio is the gearing calculator in the AVB RaceLabs Pit Kit. You give it four numbers: front (engine) sprocket teeth, rear (axle) sprocket teeth, tyre diameter in millimetres and peak RPM. It returns the ratio (rear teeth divided by front teeth, shown as x.xx : 1), rollout per wheel revolution (π × tyre diameter), distance travelled per engine revolution and theoretical speed in km/h at the RPM you entered.
At the track, most gearing debates are about one tooth. Below the main result, three cards set your current rear sprocket next to one tooth more (marked "more drive") and one tooth fewer ("more top end"), each with its own ratio and speed. You can see what the change does before you pull the chain off.
If you keep a Spares Inventory in the Pit Kit, the tooth counts of sprockets you have logged with stock show up under "Rear sprockets you own" as tap chips. Tap 80T and the calculator sets the rear sprocket to 80, so you compare gearing that is actually in the van.
The speed figure is theoretical. It ignores drag, slip and the clutch, and the app says so: treat it as a comparison between gearings, not a speedometer. Everything is calculated on the phone, so the tool works in the paddock with no signal. It is free with no cap and needs no sign-in.
