Mon Prof Augmenté
Chainring and sprocket sizes
Age 12 · Physics
Open to everyone until Monday, October 26
To keep it, print it while it is open.
A front chainring turns a rear sprocket through the chain. The size ratio between them decides how many times the rear wheel turns for one pedal stroke.
Interactive lesson
A machine to operate beside the picture: run it and watch what changes.
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In the picture
- Large front chainring: the toothed ring turned by the pedals.
- Small rear sprocket: the toothed ring at the wheel hub.
- Rear wheel: the tire and rim turned by the sprocket.
- Equal-sized rear sprocket: a sprocket with the same size as the front ring.
Examples
- A bicycle in a high gear with a small rear sprocket covers more ground per pedal.
- A bicycle in a low gear with a large rear sprocket climbs more easily.
Key takeaways
- One pedal stroke turns the rear wheel by the ratio of front teeth to rear teeth.
- A smaller rear sprocket gives more wheel turns per pedal stroke; a larger one gives fewer.
Quiz: Chainring and sprocket sizes (Age 12)
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What decides how many times the rear wheel turns for one pedal stroke?
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What happens to the wheel turns per pedal stroke when the rear sprocket is smaller?
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If the front chainring has twice as many teeth as the rear sprocket, how many times does the rear wheel turn for one pedal stroke?
The answers, each with its explanation, are in the app. This quiz is free there while the lesson is in the free week.
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