How to calculate the driving wheel and driven wheel of a motorcycle

Release date:

2025-09-19

The calculation method for the driving and driven wheels of a motorcycle primarily involves the relationships among parameters such as gear ratio, rotational speed, number of teeth, or diameter.

The calculation method for the driving and driven wheels of a motorcycle primarily involves the relationships among parameters such as gear ratio, rotational speed, number of teeth, or diameter. The specific calculation process is as follows:

I. The Basic Definition of Gear Ratio

The gear ratio (i) is the ratio of the speed of the driving wheel (n₁) to the speed of the driven wheel (n₂), expressed as:
i = n₁ / n₂
This formula applies to all transmission systems, including gears, belts, chains, and more.

II. Calculation Methods for Different Transmission Types

Gear Transmission

The transmission ratio equals the number of teeth on the driven gear (Z₂) divided by the number of teeth on the driving gear (Z₁):
i = Z₂ / Z₁
For example: If the driving gear has 20 teeth and the driven gear has 40 teeth, the transmission ratio is 2:1.
If the rotational speed is known, you can also work backward to determine the speed using the formula n₁ / n₂ = Z₂ / Z₁.

Belt/Chain Drive

The transmission ratio equals the diameter of the driven wheel (D₂) divided by the diameter of the driving wheel (D₁):
i = D₂ / D₁
For example: The driving wheel has a diameter of 10 cm, while the driven wheel measures 20 cm in diameter, resulting in a transmission ratio of 2:1.
If it's a sprocket, you can also calculate it using the number of teeth: i = Z₂ / Z₁.

Friction Wheel Transmission

The relationship between the transmission ratio and diameters is the same as in belt drives: i = D₂ / D₁.
III. Total Transmission Ratio of Multi-stage Transmission

If the transmission system includes multiple stages of gears or pulleys, the total gear ratio is the product of the individual stage ratios.
For example: In a two-stage gear transmission, if the first-stage gear ratio is 3:1 and the second-stage ratio is 2:1, the overall gear ratio will be 6:1.

IV. Precautions for Practical Applications
The relationship between rotational speed and torque: When the transmission ratio is greater than 1, the driven wheel's speed decreases while its torque increases; conversely, if the ratio is less than 1, the speed increases but the torque decreases.
Efficiency Loss: Belt or chain drives must account for efficiency losses caused by slippage or elastic deformation.
Dynamic Adjustment: The CVT continuously variable transmission uses a hydraulic system to adjust the diameters of the driving and driven pulleys in real time, enabling seamless changes in the transmission ratio.
V. Example Calculation

Scene: The driving wheel of the motorcycle rotates at 3,000 rpm, with the driven wheel having 30 teeth and the driving wheel having 15 teeth. Calculate the rotational speed of the driven wheel.
Solution:

Calculate the gear ratio: i = Z₂ / Z₁ = 30 / 15 = 2
Driven wheel speed: n₂ = n₁ / i = 3000 / 2 = 1500 rpm.

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