Live tool / crawler drivetrain

RC Crawl Ratio Calculator

Calculate total crawler reduction and rollout from your spur, pinion, internal reduction, transfer tuning, and tire diameter.

Crawler inputs

Results update as you type.

Pinion teeth

Motor gear tooth count

Spur teeth

Main gear tooth count

Internal reduction

Transmission, axle, and portal reduction before overdrive

Transfer / overdrive ratioOptional

Optional; 1.0 = none, below 1.0 = overdrive

Tire diameter

Measured outer diameter for crawler rollout

Optional comparison

Front / rear axle overdrive

Enter each axle's reduction as input turns per wheel turn (for example, 4.0 means 4:1). Leave both blank to skip.

Front axle reductionOptional · :1

Front input RPM divided by wheel RPM

Rear axle reductionOptional · :1

Rear input RPM divided by wheel RPM

Convention: wheel-speed ratio = front wheel speed ÷ rear wheel speed = rear reduction ÷ front reduction. Front overdrive % = (wheel-speed ratio − 1) × 100. Positive means the front wheels turn faster at equal axle input RPM; negative means slower.

Use your manufacturer's full drivetrain reductions where available.

Calculated setup

Crawl baseline

Total crawl ratio

1:112.0

Total reduction from motor to wheel.

Reduction split

5.60 × 20.00 × 1.00

Spur/pinion × internal × transfer

Rollout

3.4 mm

Per motor revolution · 120.0 mm tire

What this reads like

Very high reduction favors deliberate wheel speed, strong low-speed torque, and precise throttle control for technical crawling.

Typical community ranges · not hard rules

Dedicated competition crawl rigs commonly run very high reductions around 1:100 and above. Scale and trail rigs often run lower to retain more wheel speed. Motor wind, ESC settings, drag brake, tire grip, vehicle weight, and terrain all change real behavior.

Next bench step · $7

RC Setup Quickstart Pack

Turn this crawl ratio into a repeatable trail baseline. The pack gives you a compact worksheet for recording reduction, tires, motor, ESC, and test notes.

See what's in the $7 pack

Keep calculating

Compare the raw drivetrain math alongside your crawler baseline before making a hardware change.

Gear ratio Gearing planner

Loading calculator…

Setup reference

What this calculator does

Enter your crawler drivetrain ratios and tire diameter to calculate total reduction, the reduction split, and rollout. Use it to compare low-speed control and wheel travel across crawler setups.

FAQ

RC setup questions

What is a good RC crawler crawl ratio?

The useful range depends on motor type, tire size, vehicle weight, and terrain. Compare total reduction and rollout rather than relying on one universal number.

How is RC crawl ratio calculated?

Multiply the spur-to-pinion ratio by the internal drivetrain reduction and the transfer or overdrive ratio.

Does a higher crawl ratio improve control?

More reduction generally improves low-speed modulation and torque at the wheel, while reducing wheel speed for a given motor RPM.