RC Car Gear Ratio Speed Calculator
Calculate your RC car speed from gear ratio, motor, and battery specs.
Small gear on motor
Gear attached to wheel
From car manual (typical is 2.0 - 3.0)
RPM per volt (from motor spec)
3S LiPo = 11.1V, 4S = 14.8V
Typical 2.8 inch = 71mm
How do I calculate RC gear ratio?
Gear Ratio = Spur Teeth / Pinion Teeth. Lower pinion number or more spur gear = lower gearing for more torque but slower. Choose different sizes during build. Using different motor mounts adjusts pinion engagement - typical setups use 16T pinion with 48T spur, or 15T with 45T for different speeds. Higher ratios on motor output give more torque, lower speeds wheel.
What KV motor should I use for racing vs crawling?
Crawling requires low KV (1000-2500) with high gearing for torque and slow speeds. Racing uses high KV (3500-6000) for speed. Basher/bashing can use mid-range (2500-4500). Higher KV = faster but less torque. Match KV to your use terrain: rocks need low KV, open tracks need high KV, mixed conditions can use mid-range with different gearing.
What is a typical gear ratio range?
Most RC vehicles use 2.5:1 to 4:1 gearing. Lower (higher ratio number) = more torque, slower, better for rocks. Higher (lower ratio number) = less torque, faster, better for tracks. For a 3300KV motor on 3S: 3:1 = ~25mph, 2:1 = ~35mph, 1.5:1 = ~50mph. Adjust based on battery and desired top speed.
How do I estimate top speed?
Calculate motor RPM (= KV x Volts), apply gear ratio, convert to wheel RPM, calculate circumference (pi x diameter), convert to mph. Rough formula for typical 1/10 RC: (Motor KV x Volts) x Gear Ratio / 1000 = mph in perfect conditions. Real results 10-20% lower due to drivetrain loss, drag. A 3300KV motor on 3S with 3:1 gearing gives around 22 mph.