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Gearing calculator
Pick a preset, change pinion, diff gears, motor and tires, and see crawl ratio, overdrive and wheel speed update. Each stock number is labelled confirmed (a cited manufacturer source) or estimated.
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Related parts for this chassis
Drivetrain, wheel, suspension and weight-placement parts that interact with gearing and climbing.
Stock values and sources
Axial SCX10 III (LCX transmission)
| Value | Number | Status | Note |
|---|---|---|---|
| stockPinion | 14 | confirmed | [source] |
| fdrLow | 45.6 | confirmed | Low (standard) speed with 14T pinion [source] |
| fdrHigh | 31.3 | confirmed | High (optional) speed with 14T pinion [source] |
| tireMm | 120 | estimated | Typical 1.9in crawler tire. Measure yours. |
For 12T to 18T pinions we show Axial's chart value exactly. Outside that range we scale the 14T figure (FDR × 14 ÷ pinion). Scaling matches the chart within 1.3% everywhere except three entries that look shifted by one pinion size: low 12T (58.1 printed vs 53.2 scaled, which is the 11T value), high 12T (39.8 vs 36.5, the 11T value) and high 13T (36.5 vs 33.7, the 12T value). We show the published figures with a warning.
Traxxas TRX-4 (two-speed, portal axles)
| Value | Number | Status | Note |
|---|---|---|---|
| stockPinion | 11 | confirmed | [source] |
| stockSpur | 45 | confirmed | [source] |
| lowFactor | 15.8 | confirmed | Spur/pinion × 15.8 = low-gear final ratio [source] |
| highFactor | 6.32 | confirmed | Spur/pinion × 6.32 = high-gear final ratio [source] |
| axleStock | 3.0909 | confirmed | [source] |
| tireMm | 117.9 | confirmed | 1.9in x 4.64in Canyon Trail (most RTR models) [source] |
- Traxxas TRX-4 owner's manual, Motors and Gearing page (formulas and gear chart)
- Traxxas: TRX-4 overdrive explained (stock 11/34 = 3.09:1)
- Traxxas 8287 overdrive differential gears (33T ring / 12T pinion)
- Traxxas 8288 underdrive differential gears (35T ring / 10T pinion)
- Traxxas TRX-4 family comparison chart (pinion/spur, tires)
Axial SCX24
| Value | Number | Status | Note |
|---|---|---|---|
| stockPinion | 11 | estimated | Community-reported |
| transmission | 13.42 | estimated | Community-reported 11T/55T then 19T/51T (5 × 2.684). Not confirmed by Axial. |
| axle | 9 | estimated | Back-derived from a retailer listing that calls a 1T/12T axle set '33% underdrive' (12 / 1.333 = 9). Not confirmed. |
| tireMm | 57 | estimated | Typical 1.0in micro tire. Measure yours. |
Axial does not publish any SCX24 gear ratio we could find. Treat every value here as an estimate and enter your own.
Traxxas TRX-4M
| Value | Number | Status | Note |
|---|---|---|---|
| stockPinion | 11 | confirmed | [source] |
| transmission | 16.6 | confirmed | Standard (high range / trail) transmission, #9776/#9791: 16.6:1 reduction ratio [source] |
| axle | 2 | reported | Stock axle ring/pinion 24T/12T = 2:1. Traxxas doesn't print the tooth counts; this comes from Hot Racing's 'Stock (12/24)' replacement for Traxxas #9779. [source] |
| tireMm | 55.9 | confirmed | 2.2in tire (Traxxas chart) [source] |
| internal | 11.38 | unclear | Traxxas lists 'Gear Ratio (Internal): 11.38' on the Bronco page without saying what it measures. It doesn't match transmission × axle (33.2) or either stage alone, so the calculator does not use it. v1 wrongly multiplied it with 16.6 (~189:1). [source] |
Overall ratio = transmission × axle: 16.6 × 2.0 = 33.2:1 stock, which matches the community's ~33:1. Crawl transmission gives 80.6:1 and speed gives 19.4:1.
- Traxxas TRX-4M Ford Bronco (97074-1) parts list: #9776 16.6:1, #9776R 40.3:1, #9776X 9.7:1 transmission gear sets, 11T pinion
- Traxxas TRX-4 family comparison chart (TRX-4M ratios, 2.2in tire)
- Hot Racing TRXM9224: steel helical diff ring/pinion, 'Stock (12/24)' for TRX-4M, replaces Traxxas 9779
- Traxxas TRX-4M Ford Bronco specs ('Gear Ratio (Internal): 11.38')
Formulas
- Motor rpm (no load) = KV × voltage. Real speed under load is lower.
- Wheel rpm = motor rpm ÷ final drive ratio (FDR). Speed = wheel rpm × π × tire diameter.
- SCX10 III: Axial chart value for 12–18T pinions, otherwise the 14T figure × 14 ÷ pinion.
- TRX-4M: FDR = transmission (16.6, 40.3 or 9.7) × axle (stock 2.0).
- TRX-4: FDR = spur ÷ pinion × 15.8 (low) or × 6.32 (high), from the Traxxas manual. Non-stock diff gears scale it by (ring ÷ pinion) ÷ 3.09.
- Overdrive % = rear FDR ÷ front FDR − 1, which is how much faster the front wheels spin than the rears.