Gearing & speedTop speed

Gearing & top speed

Enter a car or truck setup, change one part, and see what moves.

Gearing

Pinion & spurTotal FDR

Pinion

Spur

Transmission & axle

Portal

1 if the axles have no portals

Transmission & axle is every reduction after the spur except the portal boxes, which go in their own field. Pinion and spur set the external ratio.

Tires

Outside diameter

Unit

Outside rolling diameter, not rim diameter.

Assumed tire growth (advanced)

Assumed growth

Motor & battery

KV & voltageMeasured RPM

Motor KV

rpm/V

Series cells

Reference voltage, not a charge reading. Chemistry and manufacturer limits control actual use.

Record a GPS pass (advanced)

GPS speed

mph

Change one thing

Target pinionTooth counts for a chosen speed Tire size effectRollout change and correction GPS passMeasured against theoretical Chassis & setup toolsCrawler, corner weights, springs

How this is calculated

Motor RPM is KV times pack voltage. Final drive is spur over pinion times the internal ratio. Rollout is tire circumference divided by final drive. Speed is motor RPM times rollout. The result ignores load, sag, drag, drivetrain loss and tire growth, so treat it as a ceiling for comparing setups, not a prediction.

Read the methodology