A comprehensive guide to crankset sizes and standards
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The crankset – often referred to as a chainset – is one of the most important parts of a bicycle. As one of the key components that helps move the chain as you pedal, it’s at the heart of the drivetrain and helps make a bike, well, a bike.
In this guide, we’ll tell you everything you need to know about cranksets, delving into crankset types, chainring sizes, crank length and crankset compatibility, as well as taking a closer look at road, mountain bike and gravel bike cranksets.
In short, we’ll open the Pandora’s Box that is the bicycle crankset.
Seemingly simple, there’s a wealth of complexity hidden in the bit of your bike that enables you to keep your wheels turning.
Let’s start with the basics.
The crankset is, quite simply, the part of the bike you pedal to move you and the bike forward. In North America, it’s typically called a crankset, while in the UK it’s often referred to as a chainset, although crankset or simply ‘cranks’ are still commonly used.
The crankset comprises the two crank arms to which the pedals are attached, and between one and three chainrings that the chain runs over.
In modern designs, it also typically includes the bit in the middle – the axle or spindle – that connects the two sides. In traditional cranksets, the axle is part of the bottom bracket, the bearing assembly that connects the cranks to the bike’s frame.
In combination with your rear gearing, which is usually provided by a rear derailleur and a cassette with multiple sprockets, your crankset should give you a wide enough range of gears to select one appropriate for the terrain you’re riding on.
It sounds simple, but the crankset is one of those bike components that hides its complexity in the numerous options, standards and compatibility conundrums.
Cranksets generally come with either one, two or three chainrings.
Two chainrings are most common on road bikes, while the latest mountain bikes tend to come with a single ring. Modern systems will give you plenty of range both for getting up hills and faster riding.
Single-ring systems, known as 1x drivetrains, are becoming increasingly popular on gravel bikes and can be found fitted to road bikes, too. Many 1x cranksets use narrow-wide chainrings for better chain retention.
Combined with the cassette, the number of teeth on the crankset’s chainrings will define your bike’s gearing. However, chainring sizes vary significantly, with options for every type of riding, so we’ll cover them separately below.
The chainrings are usually bolted onto arms that protrude from the right-hand crank arm, also called a spider. There are exceptions though, which we’ll come on to.
You can’t easily swap the number of chainrings your bike is set up for, because the front derailleur and associated shifter will be specific for your setup and would need to be replaced, too.
Power meters incorporated into the crankset’s arms or spider are popular with performance-focused road cyclists (and some mountain bikers and gravel riders, too). Pedal-based power meters are also popular.
There is a wide range of power meter models available – read our guide to the best power meters – but they are pricey and you may need specialist tools to fit them in place of your bike’s existing crankset.
Swapping chainring sizes on a double or triple crankset isn’t as simple as it sounds, because specific chainrings are designed to work together, with tooth positioning and ramps on the rings there to help the chain shift smoothly.
A mismatched pair of rings might make for particularly awkward shifts from the small to the large ring and there’s an increased risk of the chain falling off the rings altogether, whether you’re shifting up or down.
Groupset brands also recommend a maximum difference in the number of chainring teeth that a front derailleur can deal with, so you can’t usually increase the jump between rings.
Also, the teeth on a chainring are sized for the number of gears on your bike so you can’t, for example, use an 8-speed chainring with an 11-speed chain, because the teeth would be too wide in that instance.
If you do want to swap chainring sizes, check for compatibility beforehand.
It is a lot simpler, though, on a single-ring setup, with only chain length needing much consideration.
A variety of crank lengths are available.
The shortest is usually 165mm (measured from the centre of the bottom bracket to the centre of the pedal spindle) and they increase in 2.5mm increments up to 175mm, although there are exceptions that go longer.
The most common length found on mid-sized road bikes tends to be 172.5mm, while mountain bikes most often have 170mm or 175mm cranks.
Longer crank arms give you more leverage. You’ll find them on some larger-sized bikes, too. Be careful about fitting a longer crank to a bike than the one it came with though, because it will reduce your ground clearance if you’re pedalling through a fast corner or over obstacles off-road.
A shorter crank arm tends to enable you to keep up a higher cadence. They’re often preferred by triathletes.
Rear Derailleurs In practice, we’re only talking about a few millimetres difference between ‘long’ and ‘short’ cranks – most riders will barely notice the difference in normal riding, from one