⚙ RC Gear Ratio Calculator
Calculate final drive ratio, top speed, and roll-out for electric RC cars
| Battery | Voltage | RPM @ 2200KV | RPM @ 3000KV | RPM @ 4500KV | Typical RC Use |
|---|---|---|---|---|---|
| LiPo 2S | 8.4V | 18,480 | 25,200 | 37,800 | Stock touring, beginner |
| LiPo 3S | 12.6V | 27,720 | 37,800 | 56,700 | Modified touring, buggy, truck |
| LiPo 4S | 16.8V | 36,960 | 50,400 | 75,600 | 1/8 buggy, speed run |
| LiPo 5S | 21.0V | 46,200 | 63,000 | 94,500 | High-power speed run |
| LiPo 6S | 25.2V | 55,440 | 75,600 | 113,400 | Record speed runs |
| NiMH 6-Cell | 7.2V | 15,840 | 21,600 | 32,400 | Budget / entry level |
| NiMH 7-Cell | 8.4V | 18,480 | 25,200 | 37,800 | Budget performance |
| Pinion (T) | Spur 48T | Spur 54T | Spur 60T | Spur 68T | Spur 72T | Spur 87T |
|---|---|---|---|---|---|---|
| 12T | 4.00:1 | 4.50:1 | 5.00:1 | 5.67:1 | 6.00:1 | 7.25:1 |
| 14T | 3.43:1 | 3.86:1 | 4.29:1 | 4.86:1 | 5.14:1 | 6.21:1 |
| 16T | 3.00:1 | 3.38:1 | 3.75:1 | 4.25:1 | 4.50:1 | 5.44:1 |
| 18T | 2.67:1 | 3.00:1 | 3.33:1 | 3.78:1 | 4.00:1 | 4.83:1 |
| 20T | 2.40:1 | 2.70:1 | 3.00:1 | 3.40:1 | 3.60:1 | 4.35:1 |
| 22T | 2.18:1 | 2.45:1 | 2.73:1 | 3.09:1 | 3.27:1 | 3.95:1 |
| 25T | 1.92:1 | 2.16:1 | 2.40:1 | 2.72:1 | 2.88:1 | 3.48:1 |
| 28T | 1.71:1 | 1.93:1 | 2.14:1 | 2.43:1 | 2.57:1 | 3.11:1 |
| 30T | 1.60:1 | 1.80:1 | 2.00:1 | 2.27:1 | 2.40:1 | 2.90:1 |
| RC Class | Pinion / Spur | Diff Ratio | Final Drive | Est. Top Speed |
|---|---|---|---|---|
| 1/10 Touring Stock (2S) | 20T / 68T | 2.60:1 | 8.84:1 | ~36 km/h |
| 1/10 Touring Modified (3S) | 27T / 57T | 2.60:1 | 5.49:1 | ~80 km/h |
| 1/10 Buggy Track (3S) | 18T / 72T | 2.73:1 | 10.92:1 | ~55 km/h |
| Monster Truck Bash (3S) | 16T / 54T | 3.00:1 | 10.13:1 | ~60 km/h |
| Rock Crawler (2S) | 11T / 87T | 12.00:1 | 94.91:1 | ~5 km/h |
| Drag Car / Speed Run (4S) | 29T / 54T | 2.60:1 | 4.84:1 | ~130 km/h |
| 1/10 Short Course (3S) | 17T / 65T | 2.80:1 | 10.71:1 | ~58 km/h |
| 1/12 Pan Car (2S) | 22T / 72T | 2.40:1 | 7.85:1 | ~74 km/h |
The report of gears in rc gear cars simply said shows how far one gear rotates regarding the other. To count it, suffice to share the amount of teeth in the spur gear by that in the pinion gear. For instance, if the spur has 39 teeth and the pinion 34, then the report comes from 39 divided by 34 what results around 1.15.
The bigger that number, the less quickly the car moves.
How RC Gear Ratios Affect Speed and Torque
Some folks reverse the cause and share pinion by spur. Here counts the opposite thing, big number then points to bigger speed.
Here comes the part where it becomes truly interesting. Little report of gears helps to better speed and initial push, because extra torque backs the trip to quickly move. Big report trades a bit of that speed against higher top pace.
Big pace always means fewer grip, and little grip however forces fewer pace. The secret lies in finding the right balance, where everything feels well.
Little pinion with big spur delivers a lot more torque and speed, but fewer top pace. The opposite setup gives stronger top speed, even so less torque, and teh engine must work more hard, what creates more heat. Changing the pinion cause clearer effect on the run.
For gentle changes, swapping the spur gear is the best way. Or change both for biggest result or good balance.
However the report between pinion and spur does not form the whole picture. There also exists internal report in the gearbox. On some cars it matches 2.6.
To receive the whole total report, one multiplies the report spur-pinion by the internal. For instance, the Granite MEGA owns 15-tooth pinion and 87-tooth spur. It results in total report of 5.8 to 1.
The internal is 2.6 to 1, so the hole ends at around 15.08 to 1.
Two cars with same reports of gears can however act different, if their internal reports in the gearbox differ. Shorter report in the box does the car more quick and touchy, maybe even causing flipping. It not always matches with the desire of drivers for basic setup, when they simply want something fun and easy to drive.
For rocky crawlers, big reports of gears work more, because they deliver more torque and control for climbing on obstacles. The size of wheels also plays into the whole total report, together with the Kv of engine, what adds to how many RPM the machine reaches to spin without load. Proper starting point for report of gears are roughly 10 until 11, because the most common factory setups lie in that range.
From here, one can change according to that, as the car feels.
rc gear calculators for reports of gears exist for brands as Team Associated, Tamiya and Traxxas. Suffice to enter the internal total report, and the tool shows the whole total report together with the percent difference of share of gears. Commonly used sizes for rc gear parts include 64P, 48P, 32P and25.4P.
