Crawler Gearing Tool

RC Crawler Gearing Ratio Tool

FDR · OD% · portals · ring & pinion
How to: ① Start from Custom / blank and fill every stage yourself, or pick a stock platform and hit Load preset. ② Use the dropdowns for known gear sets, or type tooth counts / ratios by hand. ③ Read overall FDR (motor turns per wheel turn). OD% is always computed from teeth, never marketing labels. ④ Export / auto-saves in this browser. Confidence: verified likely estimated

Motor gearing (spur / pinion)

Transmission

Transfer case

Diff ring & pinion

Portal gears

Optional — crawl speed

Approx. wheel RPM & speed at full throttle (no load). Real crawl speed is lower under load.

Results

Overall FDR (high / single)
—
motor turns : 1 wheel turn
Overall FDR (low)
—
2-speed low range
Front vs rear
—
OD% / UD% from teeth
Axle total (diff × portal)
—
per end
Est. wheel RPM
—
@ full throttle
Est. top speed
—
mph · km/h

Stage breakdown

Compare front / rear

Front FDR
—
Rear FDR
—

Notes

    Setup guide — how to read these numbers

    FDR (final drive ratio) = motor revolutions for one wheel revolution. Higher = more torque / slower crawl. Typical 1/10 crawlers: mid-20s (fast) to mid-60s+ (comp crawl).

    Chain: (spur ÷ pinion) × trans × t-case × (ring ÷ diff pinion) × (portal out ÷ portal in)

    OD% is always (rear_stage ÷ front_stage − 1) × 100 from teeth when stages differ. Marketing labels (Axial “12%” vs Vanquish “9.5%” on the same 27/8 gears) are ignored for math.

    Portal axle total for Capra/AR45P stock is 30/8 × 23/12 = 7.1875 (not Axial’s old “7.39” marketing figure).

    Confidence flags come from the V1 research database. Estimated stages were back-derived from official overall FDR when manufacturers don’t publish internals.

    1Tenth · Gearing Ratio Tool v1 · Database V1 (2026-07-20) · Companion to Crawler Geometry Tool