Gear ratios on the SCX24 are not one number but a stack. Motor pinion to spur, transfer gear, axle internal gears. Multiply them together and you have the final drive ratio. Change any one of them and you change how the truck feels. This is the reference for what each ratio actually does and what you can adjust.
What gear ratio means
A ratio compares input rotations to output rotations across a meshing gear pair. Two effects fall out:
- Speed. Input RPM divided by the ratio equals output RPM. A 3:1 reduction turns 30,000 motor RPM into 10,000 RPM at the next stage.
- Torque. Output torque equals input torque times the ratio, minus 5 to 10% friction per stage. Lower output speed means higher output torque. You can't get both.
The three stages on an SCX24
Power goes from the motor to the wheels through three gear reductions:
- Motor pinion to spur. The small gear on the motor shaft drives the big spur in the transmission. Stock SCX24 spur is 48 pitch (or 0.5 Mod metric). Stock pinion is usually 11 to 13T.
- Transfer gear (inside the transmission). Drives the front and rear driveshafts off the spur.
- Axle internal gears. The worm and worm gear inside each axle. Stock is 2/16T worm.
Final drive ratio is the product of all three. Stock SCX24 final drive is roughly 8:1, depending on pinion choice.
What you can change without buying a new transmission
Three things, in order of how often builders touch them:
- Motor pinion. Change the pinion tooth count to re-gear the motor. More teeth = less reduction = more wheel speed, less torque. Common SCX24 pinions: 11T, 12T, 13T, 14T.
- Axle internal gears (OD / UD). Replace the stock 2/16T worm with 2/14T or 2/13T for overdrive, or 2/18T for underdrive. See the overdrive / underdrive explainer.
- Tire diameter. Effectively a final-stage ratio change. Bigger tires turn slower for a given wheel RPM. A 64mm tire vs. a 52mm tire is roughly a 23% “underdrive” from the truck's perspective.
What you can't easily change: the transmission internal ratio. The stock transmission is a fixed reduction. Replacement transmissions exist (LGRP, Mofo, Furitek all sell them) and are sometimes used in comp builds, but it's a deep upgrade.
Pinion pitch (this matters)
Pinion and spur have to match pitch. Stock SCX24 is 48P / 0.5 Mod. Some brushless combos move to other pitches:
- 48P / 0.5 Mod. Stock SCX24 transmission.
- 32P. Coarser teeth, more durable. Some aftermarket transmissions use this.
- 0.6 Mod / 64P. Other metric standards. Furitek and INJORA conversions sometimes use these.
Mismatched pitch strips the spur in minutes. Always confirm pitch before you order a new pinion or spur.
Common ratio changes and what they do
- Smaller motor pinion (11T to 10T). More wheel torque, slower top speed. Good for stock-class crawlers wanting more low-end.
- Bigger motor pinion (11T to 13T). More wheel speed, less torque. Good for brushless trucks where you have power to spare.
- Front axle overdrive (2/14T). Front wheels turn around 12% faster than rear. Truck pulls through corners instead of pushing.
- Front axle overdrive (2/13T). Around 18% faster. More aggressive front pull.
- Bigger tires (64mm vs. 52mm). Effectively 23% underdrive at the wheel. More crawl, less top speed.
Match ratio to your build
- Stock brushed truck: stay on stock gearing. The motor is geared for what it can do.
- Brushed upgrade (Hobbywing 1080 + 66T motor): stock gearing or one tooth bigger pinion. The 66T motor can handle a slight speed-up.
- Brushless trail (Furitek Stinger 3450KV): stock gearing is too fast. Step down pinion by 1 or 2 teeth, or run front OD to mask the speed.
- Brushless comp (Lizard Pro + 1400KV): stock gearing or one tooth bigger to recover wheel speed.
- Portal axles: already 25% underdrive at the wheel. Pair with stock motor gearing for crawl, or step up pinion to recover speed for trail.
Tools to figure out your specific math
The formula is straightforward but the numbers add up:
motor RPM × (pinion / spur) × (transfer / transfer) × (axle pinion / axle ring) = wheel RPM
Wheel RPM times tire circumference equals truck speed. Plug numbers in and you'll see why brushless on stock gearing makes the truck too fast for crawling.
For the practical front-OD upgrade itself, see the overdrive / underdrive explainer. For the broader upgrade picture, see the staged upgrade path.