Crankset Explained: Everything you need to know when buying a Bike Crankset
The crankset lies at the very heart of your bike’s drivetrain. Made up of crank arm, chainrings; the crankset needs to be strong, light, durable and of course, good value for money.
In our ultimate guide to bike cranksets, we’ll show you exactly what you need to know from what a crankset is, what’s included in a crankset, chainrings sizes, crank arm length and how to remove a crankset.
In this guide we will be looking at Road Cranksets, MTB Cranksets and BMX Cranksets.
- The crankset, also called the chainset, consists of crank arms and chainrings.
- Cranksets come in three main formats, single, double, and triple.
- The introduction of huge rear cassettes in recent years has improved the viability of single chain rings.
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What is a Crankset?
Quite simply a crankset (or chainset in the UK) is the component of the bike that you pedal to make the bike go forwards. Your chainset consists of a number of different parts – cranks and chainrings.
The crankset is one of those bike parts that appears straightforward but conceals its complexity in the plethora of variations, standards, and compatibility issues.
Two crank arms are mounted either side of the bike at 180 degrees to each other, connected by an axle. Most modern crank designs have the axle built into the crank arms, and then this axle is passed through the bottom bracket (BB) which is threaded or pressed into the frame’s BB shell.
Located at the meeting point of the seat tube and down tube. With older crankset designs the axle is part of the BB not the crankset. The pedals are then threaded to the other ends of the crank arms.
What are cranks made from?
Cranks can be made from a range of materials:
Often found on older bikes and BMXs.
Often found on high end road and MTB bikes.
Often found on low to mid-range Road and MTB.
How do I know what crankset I need?
A key consideration when upgrading or replacing crank arms or cranksets is crank length. Most cranks for road and MTB use are supplied in lengths from 170-175mm long, but riders with legs shorter or longer than the average may feel more comfortable on cranks that better match their measurements.
Options from 160mm to 180mm cover different limb lengths – it could be worth your while to research what crank length is recommended for your inside leg measurement. It is worth noting that some MTB riders will opt for a shorter crank to improve ground clearance especially in the more gravity-oriented disciplines such as downhill racing.
Chainrings enable the chain to drive the rear wheel, and are the cogs with which the chain links engage, each ring will have a number of teeth which is what determines the gearing.
They are generally made from lightweight aluminium alloy or, as is often the case with small and middle rings on mid-range cranksets, less expensive steel. There are some boutique lightweight component manufacturers who even make them out of carbon fibre!
Chainrings are traditionally bolted onto a four or five-arm spider. The size and number of chainrings will depend on the bike type and riding discipline, with BMX bikes having one chainring and road/MTB bikes having one, two or three depending on the riding discipline and desired range of gears. With the introduction of single ring’s its now common place for these set ups to have direct mount chainrings.
Other types of Chainrings:
Whilst the majority of chainrings are circular, there are some riders who will choose Oval chainrings which are designed to equalise the inconsistency of power through the pedal stroke. Riders who are fast twitch dominant – that is, with a very powerful but inconsistent pedal motion – tend to benefit most, especially during phases of consistent high power delivery, such as in time trials, sprints and breakaways.
The technology has been adopted by a number of professional riders, including former British Tour De France champ Chris Froome. Some mountain bikers also like them as some find it helps get over the pedalling “dead spot” (top dead centre).
Your choice of crankset will depend on the variety of gears you require. There are mostly three kinds.
- Single – There is only one chainring in a single-ring crankset. The mountain biking industry has widely adapted this technology. The loss of the smaller, inner ring is made up for by the single chainring’s usage of a broader range cassette. This reduces the number of moving parts, and for off road riding decreases the likelihood of the chain coming off and places for mud to gather.
- Double – The most commonly seen set up on a road bike. The double crankset gives a wider range of gears with small steps between them, enabling riders to maintain a consistent cadence (pedalling speed). These come in a range of sizes depending on the type of road riding, and rider fitness.
- Triple: An earlier style of chainset that is frequently found on touring, vintage, or more affordable bikes. Due to the third chainring, it provides a very wide range of gears while also gaining weight. Beginners will benefit from the additional support they’ll receive from the “granny ring” (the smallest ring) on challenging climbs.
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MTB Crankset: Explained
For years, MTB cranksets have been through a revolution going from the standard 3x chainset to the standard 1x today. With the majority of bikes in 2022 coming with a 1x chainset – only some entry level bikes will come with a 2x or 3x chainset.
Chainrings: MTB chainsets will use one, two or three rings, depending on intended use.
• Single ring: Single rings were originally used by gravity riders who spent most, if not all, of their time descending, and so didn’t need a wide gear range. However pioneering work by SRAM to introduce 11- and 12-speed cassettes widened the gear ratios achievable with a single ring up front, and the introduction of clutch derailleurs and narrow-wide chainrings, bringing them into the domain of enduro and cross-country riders. Today they dominate the trails because of their simplicity and chain retention.
• Double ring: Double rings are still used by some MTB riders, but their gearing ranges have been equalled by the huge ratios achieved by 11- and 12-speed cassettes used with single ring cranksets. However, some riders continue to favour their double rings despite the extra weight, and good savings can be made as quality two ring cranks continue to be released for less senior hierarchies.
• Triple ring: The development of huge cassettes mean triple ring cranksets are now all but an obsolete technology, particularly on mountain bikes, appearing only as stock on entry-level budget bikes, which you probably wouldn’t do any serious off road riding on.
It is worth noting that not all mountain bike cranksets are build the same. The crankset you choose will depend on the type of riding you do and the type of bike you ride. Cranksets designed for pedal-heavy MTB disciplines such as cross-country (XC) racing will need to be light in weight, while those aimed at the gravity market will need to be stronger at the expense of light weight and will use a narrower range of gears.
Direct Mount MTB Chainrings
Many ‘traditional’ chainrings are mounted via four or five bolts that secures the ring to a crank “spider” that is then attached to the crank arm. In more recent years, direct mount chainrings have become popular, installed directly onto an integrated crank which lacks the usual 4 or 5 arm spider.
A direct mount chainring help to simplify things creating a strong and robust system that is easier to maintain and most of time lighter as well.
Benefits of Direct Mount MTB Chainrings:
- A typical crank can be made lighter by removing the spider, which consists of the base for the arms as well as the actual arms.
- However, a highly machined crank with a mounted chainring on it results in a significant weight decrease.
- The spider is represented by the arms joining the direct mount teeth to the ring into which the teeth are machined in a direct mount chainring.
- Since a single ring replaces the middle chainring in the old 3x system, a 1x (narrow wide) chainring enables fine adjustment of the chain line.
Road Bike Crankset: Explained
Road bike chainsets are typically double chainring set ups, and usually come in one of three ring size combinations – 53/39, 52/36 and 50/34. The former geared towards advanced riders and the racing end of the spectrum, and the latter offering ‘easier’ gearing options for leisure riders.
The 52/36 (semi-compact) is the happy medium favoured by many riders these days. As well as these three combinations there has been a development in sub compact ring sizes. This has been brought about by the latest trend in gravel cycling, where riders are needing easier gears for off road riding and bikepacking.
- Traditional (standard) chainsets: will feature a double chainring setup with 39- and 53-tooth chainrings a common standard. These combined with 10-, 11-, or 12-speed cassettes offer a wide choice of gears for climbing. The big outer chainring ensures the traditional setup is more suited to hard-riding cyclists who can sustain a high pace – such as a race or training situation, or where the terrain predominantly consists of flat, smooth surfaces.
- Compact chainsets: span the mid-point between the speed of the traditional big ring and climbing power of the lower gears of the smallest ring on a triple chainset. This means the small ring can be disposed of, saving a great deal of weight. They typically feature a double chainring setup with 34- and 50-tooth chainrings, and have become incredibly popular for their combination of power and climbing credentials.
- Semi-Compact: The semi-compact, sometimes called the mid-compact, has slightly reduced gearing over the standard crankset with a 52 tooth big chain ring and a 36t small ring. It bridges the gap between the easier compact gears and the faster standard gears. This is a hugely popular choice among modern cyclists, providing the full gamut of speed while making the climbs a little more manageable.
- Compact: As mentioned above, the traditional compact offers 50/34 tooth chainsets, providing a trade off in favour of power over climbing. While it lacks the all-out speed of the standard racing 52 tooth ring, it strikes a good balance between speed, acceleration, and climbing gears.
- Sub-compact: The sub-compact drops the gear spread down to 46/30, perfect for big climbs or more leisurely cycling. However, where they’ve really come into their own is on the gravel bike, facilitating transition from fire road to trunk road, and mountain climb to trail.
- Single chainsets: Uses the same wide cassette technology as single-ring mountain bike chainsets. Not often seen on road bikes, their popularity is growing and used by a increasing number of professional race teams to varying levels of success. It is commonly used on Cyclocross and Gravel bikes.
A further option, but generally only seen on entry-level bikes, is the triple chainset with rings of 30-42-53 teeth. This provides the ultra-low ‘granny gear’ option for ‘sit and spin’ type hill climbing and adds extra weight.
Road Bike Crank length:
Most road cranks are supplied in sizes from 170 to 175mm in length, but riders with legs shorter or longer than the average may feel more comfortable on cranks that better match their measurements. Options from 160mm to 180mm cover different limb lengths – it could be worth your while to research what crank length is recommended for your inside leg measurement.
The vast majority of road cranksets will use aluminium cranks but carbon fibre versions for ultimate weight savings can be found on top-end models.
Chainrings: As above, road chainsets will usually use two rings with the traditional 39-53 setup geared towards race riders and the 34-50 compact chainset favoured by climbers and leisure cyclists. Alternatively, you can opt for a triple ring for the maximum range of gears.
BMX Crankset: Explained
BMX cranksets are generally consist of the crank arms, axle (spindle) and any necessary bolts and spacers.
As with all BMX components, they need to be tough, and able to withstand the pressure of hard impacts on concrete, riding on rails, stacking big jumps and tricks. For this reason, most BMX cranks are made from steel, with higher-end cranks featuring lighter cromoly steel.
Some race cranks may be made from aluminium or even carbon fibre to shed weight, but the majority are tough, dependable – and fixable – steel.
Which BMX crankset is right for me?
BMX cranks fall under four main camps: three-piece, two-piece, one-piece and race cranks.
- Three-piece: This is the most common type of crankset found on freestyle BMX bikes and features two separate crank arms which attach to a splined axle.
- Two-piece: Two-piece cranks feature the axle integrated into one of the crank arms. In most cases three-and two-piece cranksets are compatible with the same bottom brackets so long as the axle is the same diameter. They are commonly used in conjunction with the mid-style bottom bracket standard.
- One-piece: This is where the axle and crank arms are a single piece of steel. Most commonly found on entry-level or kids’ bikes. They require the use of American-style bottom brackets.
- Race cranks: These may be closer in spirit to MTB cranks, using an external BB and aluminium or carbon crank arms to save weight. They may be available in two- or three-piece versions. They require the use of euro-style bottom brackets.
When replacing or upgrading your BMX crankset it’s essential to get the sizing right. The two most important factors are axle diameter and crank length.
- Axle diameter: The two common axle diameters are 19mm and 22mm, so check before you buy that your bottom bracket is compatible. Axles will also be made with different spline patterns – 48-spline, 16-spline and 8-spline are the three most common standards. Check both axle diameter and spline pattern to ensure that your existing sprocket will fit on your new cranks.
- Crank length: This is measured from the centre of the bottom bracket axle to the centre of the pedal axle. Most stock bikes have cranks of 170mm or 175mm, but you can get them as short as 140mm and as long as 190mm. Choose crank arms that suit your inside leg measurement for optimum comfort and control.
- BMX Chainrings: Chainrings standard on BMX have changed in recent year, with old BMX bikes often coming equipped with a 48T sprocket. Today, BMX’s commonly come with a 25T or 28T sprocket fitted to one of two basic sprocket types. Bolt drive is when the sprocket is attached to the crank arm with a bolt. And Spline drive is placed straight onto a 48-spline spindle.
Bike Crankset: Common Asked Questions
Chainline – What is it and why does it matter?
Chainline refers to how straight the chain runs from the front chainring(s) to the rear sprockets. The perfect chainline is ideally when both sprockets are in the same plane, this reduces sideward motion or stress on the chain.
The chainline is significant because different mountain bikes use different rear wheel axle-width specifications. The chainring must be at a different distance from the axis in order for the bike to function smoothly across the range of gears because the cassette is at a varied distance from the bike’s centerline with different standards.
To measure your chainline you take a measurement from the centerline of the frame to the center of the chain.
You can measure the front chainline directly with a simple ruler. Simply hold the ruler against the seat tube or down tube and measure the distance from the middle of the seat tube to the middle of the chainring teeth. In the case of triple chainwheel sets, measure to the middle chainring. In the case of doubles, measure to the halfway point between the two rings.
When should a crankset be replaced?
Often cranks shouldn’t be needing replaced unless they are crashed, damaged or not looked after however to keep them in good shape, parts like chains should be replaced before they wear and cause damage.
Your chain should be replaced every 2,000 – 3,000 miles depending on your riding style. However, the best way to determine if you need a new chain is by using a chain wear indicator, which will measure how badly your chain has stretched.
If your crank is starting to show signs of wear – such as noise whilst riding – then you are in need of a new crankset. Using the same damaged one will not only cause accidents but lead to more damage.
How to remove a crankset?
If you are looking to fit a new bottom bracket or wanting to replace old chainrings – then you’ll need to get your cranks off. Removing your crankset can be an easy do it yourself job or one that you take to your local bike shop. If you are looking to do it yourself, here are a few steps to removing your crankset:
- Loosen the non-drive side crank bolts: Using a 4mm Allen key, you can loosen up the bolts that hold the left-hand (non-drive) side crank off the crank spindle.
- Remove the adjustment cap: On Shimano cranks they have a special cap that protects the spindle and bottom bracket. Using the bottom bracket tool, fit the smaller ring into the crank arm and unscrew.
- Remove the crankset: it should be simple to remove the left-hand (non-drive) crank from the spindle. After taking it out, you ought to be able to extract the right-hand (drive) crank (complete with the spindle connected) from the bottom bracket.
Depending on your crankset, the way you remove it may differ! If you are struggling to remove it you can speak to one of our tech experts who can help you out!
What is a boost Hub and does it affect my crankset?
In more recent years, there has been the emergence of boost hubs on many mountian bikes. The benefits of a boost hub and wider axle standard is given the wider hub flange, and the stronger spoke-bracing angle, the stiffness and stability of the wheel is massively enhanced.
Due to this new technology, cranksets have had to change to ensure you are still achieving the perfect chainline. It’s important to check if you are looking to change your crankset whether you have a boost hub or not.
Find out more information on Boost Hubs here!