gear ratio
To get a 1:5 ratio, the wheel gear must be 5 times larger than the motor gear.
Common Combinations:
- 9-tooth motor sprocket $\rightarrow$ 45-tooth wheel sprocket.
- 10-tooth motor sprocket $\rightarrow$ 50-tooth wheel sprocket.
- 11-tooth motor sprocket $\rightarrow$ 55-tooth wheel sprocket.
Small Wheel Bicycle Drivetrain Specifications (12" - 16")
For small-diameter wheels, the gear ratio is designed to balance pedaling effort with the shorter distance traveled per wheel revolution. Most bikes in this category use a Single-Speed Freewheel system.
1. Typical Tooth Counts by Wheel Size
| Wheel Size | Front Chainring (Teeth) | Rear Cog (Teeth) | Gear Ratio | Purpose |
|---|---|---|---|---|
| 12-inch | 24T - 26T | 16T | 1.50 - 1.62 | Maximum torque for toddlers/beginners. |
| 14-inch | 28T | 16T | 1.75 | Balanced ratio for neighborhood riding. |
| 16-inch | 28T - 32T | 16T or 18T | 1.77 - 2.00 | Higher top speed for older children. |
2. Component Anatomy
-
The Rear Cog (The Driven Sprocket): * Standard Size: 16T is the industry default.
- Thread Type: Most use a standard 1.375" x 24 TPI (Threads Per Inch) interface, allowing you to swap cogs easily.
- The Front Chainring (The Drive Sprocket): * Larger wheels require more teeth on the front to prevent "ghost pedaling" (where the legs move too fast for the speed of the bike).
- The Chain: * Standard small bikes use a 1/2" x 1/8" chain (wider than multi-speed chains).
bicycle gear
| Feature | Freewheel (Old Standard/Budget) | Cassette (Modern/Performance) |
|---|---|---|
| Mounting | Screws onto threads on the hub. | Slides onto a splined "freehub" body. |
| Mechanism | Ratchet is inside the gear cluster. | Ratchet is built into the hub (freehub). |
| Replacement | You replace the gears and ratchet together. | You replace only the gear cluster. |
| Axle Strength | Higher risk of bent axles (bearings are further in). | Lower risk (bearings are positioned further out). |
| Feature | Freewheel (Live Flywheel) | Fixed Gear (Dead Flywheel) |
|---|---|---|
| Coasting | Can coast; pedals can remain stationary while the bike moves. | Cannot coast; if the wheels are turning, the pedals must turn. |
| Reverse Pedaling | The pedals spin freely backward without affecting the wheel. | Used to reverse the bike or apply "back-pressure" to slow down/brake. |
| Mechanical Link | Connected via a one-way ratcheting mechanism (clutch). | Directly "fixed" or bolted to the hub; no internal moving parts. |
| Primary Use | Standard commuter bikes, vintage mountain bikes, most kids' bikes. | Track cycling (velodrome), "Fixie" culture, and some indoor trainers. |
Cassette
Common Freewheel Thread Standards
| Standard Name | Metric Diameter (Approx.) | Imperial Specification | Common Application |
|---|---|---|---|
| Standard ISO/English | 34.92 mm | 1.375" x 24 TPI | Most bicycles (95%); this is the "34mm" you see. |
| BMX / Metric Small | 30.00 mm | 1.181" x 30 TPI | Small freewheels (under 16 teeth) for BMX. |
| French Standard | 34.70 mm | M34.7 x 1.0 mm | Vintage European bikes (now obsolete). |
| Italian Standard | 35.00 mm | 35mm x 24 TPI | Vintage Italian racing bikes. |