Bike gear calculator

What rollout is

It's how many metres you travel with one full pedal revolution: wheel circumference × chainring teeth ÷ cog teeth. A 50×11 on road wheels covers almost 9.6 m per stroke; a 34×28 about 2.6: that's your gearing range.

Comparing cassettes

Before buying a new cassette (or going 1×), compare ranges: do you need more climbing ease (shorter lowest gear) or more top-end (longer highest)? Also check the jumps between adjacent cogs: small jumps = always the right cadence.

Cadence

Speed is rollout × cadence: at 90 rpm each metre of rollout is worth 5.4 km/h. Trained cyclists pedal at 80-100 rpm; grinding below 70 on long climbs taxes muscles more than lungs.

Why metres of development and not the gear ratio

Saying «50 by 11» means nothing until you know the wheel: the same ratio on a 700 wheel and on a 26-inch one gives different speeds. Development in metres brings together the three things that count — chainring, sprocket and circumference — and returns a single number, the metres covered per pedal revolution, which can be compared across different bikes.

It is also the number that answers the practical question: at ninety revolutions a minute, every metre of development is worth 5.4 km/h. With seven metres of development you are therefore doing about 38 an hour, and from there everything else can be read in your head.

Cadence is a choice, not a given

The same speed can be made with a long gear and few revolutions or with a short one and many: in the first case the legs pay, in the second the lungs and the heart. Trained cyclists usually sit between eighty and a hundred revolutions a minute because in that band the muscle tires less, but there is no right number for everybody.

Uphill the cadence falls naturally and the problem becomes a different one: if the easiest gear you have forces you below sixty revolutions, the climb is done on strength, and the knees notice. It is the main reason it is worth looking at your gearing before entering a mountain sportive.

The number to look at when changing cassette

Not the teeth, but the range: what minimum development you get and what maximum. The minimum says whether you will get up, the maximum whether you can push downhill without spinning out. Almost always someone changing cassette wants a shorter minimum, and at the same time discovers the jumps between gears getting wider.

That is the underlying trade-off: wide range or close jumps, not both. A cassette with few teeth of difference between one sprocket and the next lets you stay at your preferred cadence, but has no gear for a hard climb; a wide-range one climbs anything and on the flat forces you to jump between two uncomfortable cadences.

Single chainring, and what is really lost

Removing the small chainring simplifies everything: fewer levers, fewer adjustments, no chain dropping. In exchange part of the range is lost, and recovering it requires very wide cassettes, with the resulting jumps. On a mountain or gravel bike, where the cadence is already irregular and the whole range is needed, it is nearly always a good choice.

On a road bike, where hours are spent on the flat at steady cadence, the wide jumps are felt more, which is why the double survives. In both cases the sum worth doing before buying is the minimum development: if on your local climb the easiest gear is not enough, no other advantage makes up for it.

Nearby tools

For power there is FTP power zones, for heart rate Heart rate zones and for consumption Calories burned. For gradients Slope calculator, and for the electric car Electric or petrol cost per km.