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RC Car Speed Calculator

Estimate theoretical RC car speed from motor KV, battery voltage, final drive ratio and tire diameter.

Power

Gearing

Tire

Speed unit

Result

Theoretical top speed
29.2mph
(47.1 km/h)
Final drive ratio
10.76
Motor RPM (no-load)
24,420RPM

Theoretical no-load estimate — not a GPS-measured speed.

Formula

  1. 1.V = Cell Count × 3.7 V (nominal LiPo voltage)
  2. 2.FDR = (Spur Teeth / Pinion Teeth) × Internal Ratio
  3. 3.Motor RPM = KV × Voltage
  4. 4.Wheel RPM = Motor RPM / FDR
  5. 5.Speed (km/h) = Wheel RPM × π × Tire Diameter (mm) × 60 / 1,000,000

Worked example

  1. 1.Inputs: 3300 KV motor, 2S LiPo (7.4 V nominal), 87 T spur, 22 T pinion, internal ratio 2.72, 110 mm tires.
  2. 2.FDR = (87 / 22) × 2.72 = 3.9545 × 2.72 ≈ 10.76
  3. 3.Motor RPM = 3300 × 7.4 = 24,420
  4. 4.Wheel RPM = 24,420 / 10.76 ≈ 2,270
  5. 5.Speed = 2,270 × π × 110 × 60 / 1,000,000 ≈ 47.1 km/h ≈ 29.3 mph

Assumptions and limits

  • This is a theoretical no-load estimate based on the voltage you enter — not a GPS-measured speed.
  • Real speed is lower once voltage sag, load, drivetrain losses, tire deformation and surface conditions apply.
  • No fixed efficiency percentage is assumed; do not treat the result as guaranteed real-world speed.

Related tools

Guides and concepts

FAQ

Is this my real top speed?

No. The result is a theoretical no-load estimate. Voltage sag under load, drivetrain friction and tire deformation all reduce real speed.

Which voltage should I enter?

Use the LiPo cell count for nominal 3.7 V per cell, or tick Custom voltage to enter a specific pack voltage such as a fully charged 8.4 V 2S.

Where do I find the internal gear ratio?

It is the fixed transmission ratio inside your car (for example 2.72 on many 1/10 buggies). Check the kit manual — it is not the spur/pinion ratio.

Assumptions

  • No-load motor RPM is used in the calculation.
  • 3.7 V per LiPo cell (nominal voltage).
  • No drivetrain loss is applied (ideal conditions).