Bike gear ratio

Count the teeth, pick your tyre, and see how hard each gear is and how fast it goes. Useful when planning a hilly ride or choosing a new cassette.

Your details

50 x 17 on 700 x 28c

2.94

gear ratio

Gear inches78.7
Distance per pedal turn6.28 m
Speed at 90 rpm21.1 mph (33.9 km/h)
Gain ratio with 172.5 mm cranks5.80
Wheel circumference used2,136 mm
Compare a gearadd a second chainring and sprocket to see how much harder or easier it is

Lower numbers are easier gears for climbing; higher numbers are for speed. Pick the gear that lets you spin smoothly rather than grind, especially on hills.

The working

50 x 17 on 700 x 28c tyres

50 ÷ 17 = a ratio of 2.94. The wheel goes round 2,136 mm per turn, so one pedal turn moves you 6.28 m. That is 78.7 gear inches, and at 90 rpm about 21.1 mph (33.9 km/h).

What the numbers mean

Easy to hard

Gear inches	Feels like
under 30	tiny gear for steep climbs
40 to 60	easy riding and gentle hills
60 to 90	flat roads, steady pace
over 100	fast descents and sprints

Choosing gears

Before a hilly ride

Check your lowest gear: small ring and biggest sprocket
A smaller chainring or bigger sprocket makes climbs easier
Avoid big ring with biggest sprocket: it wears the chain
Fatter tyres raise the gear a touch

Gain ratio and comparing gears

Fairer numbers between bikes

Gear inches ignore crank length, so Sheldon Brown proposed the gain ratio: wheel radius divided by crank length, times the gear ratio. It is how far the bike moves for each unit the pedal moves. A 50 x 17 on 700 x 28c tyres with 172.5 mm cranks gives about 5.8; shorter cranks make the same gear feel a little harder.

Add a second chainring and sprocket to compare. A 34 x 28 climbing gear is about 59% lower than a 50 x 17, which is why compact chainsets help so much on steep hills.

Read with care

What this cannot tell you

Tyre pressureReal circumference shrinks a little under your weight.
Hub gearsInternal hubs have their own ratios.
EffortThe same gear feels harder into a headwind.

Questions

Common questions

What are gear inches?

The size of an old penny farthing wheel that would go the same distance per pedal turn.

What gear ratio is best for climbing?

A low one, often under 1:1, such as 34 x 34.

How do I measure my tyre circumference?

Mark the tyre and the floor, roll one turn with your weight on, and measure.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Before you push on

New to exercise, or got a heart, lung or joint condition? Have a word with your GP or practice nurse first. Stop and get help if you feel chest pain, faintness or unusual breathlessness, and call 999 if it is severe.