18T pinion, 50T spur
A 18T pinion on a 50T spur is a 2.778:1 spur ratio. With an assumed 2.8:1 internal ratio that is a 7.78:1 final drive, which on a 2200KV motor at 4S with 6.1 in tires works out to about 76 mph theoretical and 64.6 mph realistic.
5Pcs Mod 1 Hardened Steel Pinion Gear Set 12T 14T 16T 18T 20T
Pinion sets in Mod 1, the pitch this 50T spur uses. Buying a set lets you step one tooth at a time instead of guessing.
$12.99 listed price, changes often
Check price on AmazonWhat final drive does 18/50 give?
The spur ratio is 50 / 18 = 2.778. Your car's transmission or differentials multiply it. The internal ratio varies by model, so here is the final drive across the common range; find yours in the manual next to the gearing chart.
| Internal ratio | Final drive (FDR) | Character |
|---|---|---|
| 2:1 | 5.56:1 | tall: speed, more heat |
| 2.5:1 | 6.94:1 | tall: speed, more heat |
| 2.72:1 | 7.56:1 | tall: speed, more heat |
| 3:1 | 8.33:1 | typical 1/10 basher range |
| 3.5:1 | 9.72:1 | typical 1/10 basher range |
How fast is 18/50?
Example: a 1/10 4S monster truck, 2200KV motor, 6.1 in tires and an assumed 2.8:1 internal ratio (FDR 7.78:1). Theoretical speed is a no-load ceiling; the realistic figure assumes about 85 percent of it, which is typical on stock tires. For your own motor and tires, use the gear ratio and top speed calculator.
| Battery | Motor RPM | Theoretical | Realistic |
|---|---|---|---|
| 4S LiPo (14.8 V) | 32,560 | 76 mph | 64.6 mph |
What does one tooth up or down do?
Speed scales with the pinion on a fixed spur. The heat rating compares each option with 18T, assuming 18T runs at a sensible temperature today.
| Swap | Speed change | Motor heat |
|---|---|---|
| 18T to 16T | -11.1% | cooler |
| 18T to 20T | +11.1% | moderate |
Which cars use a 50T Mod 1 spur?
The 50T spur on this page is listed as fitting the Traxxas 1/10 Maxx, sold with a 20T pinion. Pitch matters more than tooth count: Mod 1 gears only mesh with Mod 1 gears. Set the mesh with a strip of paper between the gears as you tighten the motor, then remove it; there should be a tiny amount of play. See how to change a pinion gear.
18T on other spurs
- 18/86 (48P): 4.78:1
- 18/90 (48P): 5.00:1
- 18/83 (48P): 4.61:1
- 18/76 (48P): 4.22:1
- 18/57 (0.8 mod): 3.17:1
- 18/46 (Mod 1): 2.56:1
Every pinion on the 50T spur
Gears and a thermometer for this swap
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Frequently asked questions
What is the gear ratio of 18/50?
50 divided by 18 is 2.778, so the spur ratio is 2.78:1. The final drive ratio multiplies that by your car's internal transmission or differential ratio, which is printed in the manual. At a 2.72:1 internal ratio it is 7.56:1; at 3:1 it is 8.33:1. Use the calculator with your own internal ratio for an exact figure.
Is 18T faster than 17T on a 50T spur?
Yes. On the same spur, speed scales with pinion teeth, so 18T is about 5.9 percent faster than 17T at the same motor RPM. The motor also works harder at every speed, so it runs warmer. Check the temperature after two or three minutes of running before going up another tooth.
Will a 18T Mod 1 pinion fit my car?
Only if the spur is also Mod 1 and the motor mount has enough adjustment for the pinion size. Pitch must match exactly; Mod 1 gears will not mesh correctly with other pitches. Bore size must match the motor shaft, commonly 3.175 mm (1/8 in) on 1/10 motors and 5 mm on larger motors. The spur here is listed as fitting the Traxxas 1/10 Maxx, sold with a 20T pinion.
RCCarCalc is researched guidance, not professional advice. Figures come from published manufacturer specifications, listings and verified owner reports, not hands-on testing. Speeds are theoretical or as listed; real results depend on gearing, battery, tires and terrain. See how we research.