Advertisement

Sign up for our newsletter

Advertisement

Bicycle gear ratios explained

Road and gravel bikes now have more gearing options than ever before, but how do gear ratios actually work?

Stu Bowers
31 May 2022

The first bicycles had only one gear. By the mid-19th century, this had increased to two, and the number of gears has risen consistently ever since such that today it is possible for a bike to have 81 gears (oh yes it is: a Sturmey Archer CS-RK3 internally geared three-speed hub with a nine-speed cassette and a triple crankset, since you ask).

Of course, more isn’t necessarily better. It’s the range – the ratios – that matter most in gearing, and in that regard, we have never been more spoilt.

The trick is to know which combination of gears will work best for you.

Not so long ago, most road bikes came with a ‘standard double’ crankset (or chainset, if you prefer). That is, a big ring with 53 teeth and a smaller 39-tooth ring.

Then along came the ‘compact’ crank – popularised by FSA in the early 2000s – with 50/34 chainrings.

Since then we’ve seen the advent of the ‘mid-compact’ 52/36 crankset, and then the ‘super-compact’ 48/32 crankset, plus numerous other variations on the theme.

While all this has been going on at the front of the drivetrain, at the rear there has been an equally rapid growth in the number of cassette variations.

The once ubiquitous 11-23 cassette has given way to a wide range of options, from a tiny 9-tooth sprocket up to a dinner plate-sized 42-tooth. These days it's not uncommon for a road bike to come with a 10-33 or 11-34 cassette as standard, while a gravel bike might feature a 10-36, 11-40 or one of countless other options. 

Cycling gear ratios: 12-speed options

With all the main groupset manufacturers – Shimano, SRAM and Campagnolo – now offering 12-speed drivetrains, the jump between gears need not be huge, even with a very wide range.


Related reading:

Buyer’s guide to Shimano road and gravel groupsets Buyer's guide to SRAM road and gravel groupsets Buyer's guide to Campagnolo road and gravel groupsets


But it’s not just the sprocket and chainring sizes that affect gearing. The size of tyres and length of cranks also have an impact, so it’s worth understanding a bit about how gear ratios are calculated.

Without getting too geeky, a gear ratio allows you to understand how far the bike will travel for every turn of the pedals, and the starting point is to simply divide the number of teeth on the chainring by the number of teeth on the cassette sprocket.

For example, a 50×11 gear equates to a ratio of 4.55, usually expressed as 4.55:1. In other words, in this gear the rear wheel will turn 4.55 times for every crank revolution. If the sprocket and chainring are of equal size the ratio is 1:1.

How do I calculate bicycle gear ratios?

SRAM Force 1 cassette

From here, we can work out how far the bike will travel per pedal revolution – known as ‘metres of development’ – by measuring the wheel circumference, which is where tyre size becomes an issue.

If we’re riding in a 50×11 gear, a 700c × 28mm tyre (circumference 2,136mm) will travel 9.71m per pedal revolution, while a 700c × 32mm tyre (circumference 2,155mm) would travel 9.80m.

That means with each turn of the cranks, the bigger tyre carries the bike 9cm further.

It’s worth remembering that the size of the sprocket tends to have a bigger effect on the gear ratio than the size of the chainring. Or to put that another way, a 44×9 gear is actually bigger than 53×11.

That’s an extreme example, but it suggests that the need for large chainrings may be diminishing and that it is feasible for most riders to get all the gears they need from a single, smaller chainring.

Rise of the 1× drivetrain

In 2018, ill-fated pro team Aqua Blue became the first professional outfit to compete at WorldTour level using just 11 gears.

With a single chainring at the front and a wide-range cassette at the back (a system known as 1×, or ‘one-by’), it’s possible for a smaller number of gears to provide enough range to ride effectively, although the approach has not proved popular in the pro peloton, and Aqua Blue's ultimate failure was messy and public.

There will be those traditionalists who insist that a bike simply won’t be able to go fast enough without a meaty 53t chainring up front, but the maths suggests otherwise.

A single 46t chainring, paired with an 11t sprocket, ridden at 100rpm (perfectly within the bounds of normality) with 28mm tyres, gives a theoretical speed of 53.42kmh. That should be more than sufficient for most riders.

‘There’s so much bravado around gearing,’ says Phil Burt, former head of physiotherapy at British Cycling and founder of bike fit specialist Phil Burt Innovation.

‘Riding a compact might have a stigma attached to it, just like riding with an upright stem, but if it means you don’t get back and knee problems and you can ride the bike more comfortably, then so what?

‘You need to think about it more as a tool to do the job, not what it looks like.’

1× may not have caught on for road bikes as yet, but it's hugely popular in gravel circles, and gearing options have never been better with a host of 1×12 drivetrains on the market, and even 1×13 in the form of Campagnolo Ekar and lesser-spotted and unimaginatively named Rotor 1×13 groupset.

Up to speed on gearing ratios? Head onto the next in our series on bike fit variables to get a handle on the effect of head angle on handling



This article first appeared on Cyclist in 2018 and has since been updated with contributions from our team of experts.

Read more about: