Understanding Gear Inches and Development
If you've looked at track cycling results or European race regulations, you'll have seen gearing expressed in "gear inches" or "development" rather than the rollout in metres that British Cycling uses. Here's what these measurements mean and how they relate to each other.
Three Ways to Measure the Same Thing
There are three common ways to express how "big" a gear is. They all describe the same underlying concept — how far the bike moves per pedal revolution — but they use different units and reference points:
Rollout (metres)
The distance the bike travels in one complete pedal revolution. This is what British Cycling uses for its gear restrictions. It takes into account the chainring, sprocket, and actual tyre size.
Rollout = (Chainring / Sprocket) × Wheel circumference
Gear Inches
An older measurement system that originated in the penny-farthing era. It tells you the equivalent diameter (in inches) of a penny-farthing wheel that would travel the same distance per pedal revolution.
Gear inches = (Chainring / Sprocket) × Wheel diameter (in inches)
For a standard 700c wheel with a 25mm tyre, the wheel diameter is approximately 26.3 inches. So a 48/16 gear ratio gives: (48/16) × 26.3 = 78.9 gear inches.
Development (metres)
Used widely in Continental Europe (especially France, Belgium, and the Netherlands), "development" is simply the French/Dutch word for rollout. It's the same measurement as rollout in metres — the distance travelled per pedal revolution. When you see "développement" in French race regulations, it means rollout.
Converting Between Them
Conversion formulas
- Gear inches to rollout: Rollout (m) = Gear inches × 0.0798 (approximately)
- Rollout to gear inches: Gear inches = Rollout (m) ÷ 0.0798
- Gear inches to rollout: More precisely, multiply gear inches by π and convert to metres: Gear inches × 3.14159 ÷ 39.37
For quick mental maths: gear inches × 0.08 gives a rough rollout in metres. So 75 gear inches ≈ 6.0m rollout.
Where Each System Is Used
- British Cycling — rollout in metres. This is what you'll encounter at most UK road and circuit races.
- Track cycling (UK and international) — often gear inches, especially at velodromes. The track calculator handles this conversion for you.
- UCI / European events — development in metres (same as rollout). European federations like the FFC (France) and KNWU (Netherlands) specify limits in metres.
- US cycling — gear inches is the traditional standard, though metric rollout is becoming more common.
Why It Matters for Junior Racing
If your child races track events, you'll likely encounter restrictions expressed in gear inches. If they race European events, you'll see restrictions in metres (development). The actual limit is the same — it's just expressed differently.
The important thing is to check which unit the event regulations use and make sure you're comparing like with like. A limit of "75.4 gear inches" is approximately 6.01m — very close to the standard 6.05m British Cycling limit, but not identical.
Use the gear calculator to check your rollout in metres, and the track calculator for gear inches. Both give you instant answers without needing to do the conversion yourself.
A Quick Reference
Common rollout limits in both units
- 5.40m rollout = approximately 67.7 gear inches
- 6.05m rollout = approximately 75.8 gear inches
- 6.10m rollout = approximately 76.4 gear inches
- 6.45m rollout = approximately 80.8 gear inches
- 7.01m rollout = approximately 87.8 gear inches
- 7.93m rollout = approximately 99.3 gear inches