RC Crawl Ratio Calculator
Total gear reduction from motor to wheel for rock crawlers and trail trucks, including transmission, axle and portal gears.
Gearing
Teeth on the motor gear.
Teeth on the spur gear.
Internal reduction, from your manual. Use the gear you drive in (low on a 2-speed).
Ring ÷ pinion teeth in the axle, e.g. 30/13 = 2.31.
Portal or planetary hubs. 1 if your axles have none.
The starting values are an example, not a specific truck. Your kit manual lists the transmission and axle ratios, and often the total internal ratio.
Wheel speed (optional)
Add your motor to see how fast the truck crawls at full throttle.
Brushless Kv. Leave blank to skip.
2S = 7.4, 3S = 11.1.
1.9" crawler tires are ~4.5–5".
Crawl ratio
35.0:1
Trail truck range. A common all-round range for scale trail trucks.
Free app for crawl comps
Running or judging a crawl comp? Score it on your phone.
RC Crawl Scorekeeper replaces the clipboard, with custom rules and time limits for your club. For big events, judges upload to CrawlScore.com and scores tally automatically.
What is crawl ratio?
- • Crawl ratio is how many times the motor turns for one turn of the wheels: (spur ÷ pinion) × transmission × axle × portal.
- • A higher ratio means slower wheel speed, more torque at the wheel and finer throttle control on rocks, at the cost of top speed.
- • Trail trucks often run somewhere around 30–60:1, and competition crawlers commonly go much higher, often 80:1 and up. The motor matters too: a high-Kv motor needs more reduction for the same wheel speed.
- • The quickest way to change it is the pinion/spur pair. Swapping a 12T pinion for a 10T raises the ratio by 20%.
- • For pinion, spur and rollout on non-crawlers, use the gear ratio calculator.
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