Report short road bike cranks: Want to shorten the crank?

In 2024, Tadej Pogacar raced to his victories on 165 millimetre short cranks. These cranks are normally used by smaller riders who are also travelling on correspondingly small wheels. However, at 1.76 metres, Pogacar is of normal height and rode 172.5 millimetre cranks in 2022 - the standard length for medium frame sizes. However, Pogacar is not alone on this shrinking path. Shorter cranks have been in vogue for some time now. The wave was kicked off by time trialists, especially triathletes. The argument in favour of the shorter cranks: a wider hip angle and therefore the ability to bend the upper body lower to improve aerodynamics. The trick is not new. Back in 2015, Bradley Wiggins shortened the cranks on his bike from 177.5 to 170 millimetres in one fell swoop for his - successful - attack on the world hour record, which, according to his bike fitter at the time, Phil Burt, enabled him to lower the handlebars by 30 millimetres and optimise his already very fast position even further. His cwA value is said to have improved by just over three per cent at the time. The trend towards shorter cranks contrasts with the fact that professional cyclists have historically tended to choose longer cranks than the standard size. Tall riders anyway, but also petite riders, such as Marco Pantani. The Italian, 1.72 metres tall, chose cranks up to 180 millimetres long on the climbs, but rode 170 millimetres on the flat.

Short or long, which is right?

With complete bikes, bike manufacturers are also faced with the question of which crank length should be fitted to which frame size. Only three lengths are used in series production: 170, 172.5 and 175 millimetres. In light of the latest developments, however, shorter cranks are increasingly being used on very small sizes. For example, Canyon supplies its Aeroad in size XS with 165 mm cranks. However, this is more suitable for riders who are significantly smaller than Pogacar. Canyon's frame size 2XS is suitable for riders between 1.50 and 1.65 metres tall (68 to 79 centimetres inside leg length). The next larger Canyon frame size already has 170 millimetre cranks because Shimano only offers the 167.5 millimetre intermediate size for the top-of-the-range Dura-Ace groupset, which bike fitter Franziska Schmidt also criticises.

SRAM, on the other hand, would have 167.5 millimetre cranks in its range, but Canyon does not specify them on SRAM models. In principle, all manufacturers follow the idea of selecting cranks according to frame and body size, but the changes in length of the cranks are heavily damped. The range from 165 to 175 millimetres means a spread of only six per cent, whereas body sizes and leg lengths vary by 25 per cent across the range of frame sizes. Anyone who wants to choose their cranks in proportion to their leg length and is significantly shorter or taller than average will therefore only find what they are looking for with specialists who also offer extreme lengths. What does science say about crank length?

The state of the (somewhat thin) research on the subject of crank length states that differences in length of ten millimetres and more have no influence on performance. Based on this, cranks could therefore be selected according to other criteria, for example purely from a fitting point of view. These could be: pain-free, more comfortable or more aerodynamic to sit on and ride. In any case, a shorter crank makes it easier to position the rider, because shorter cranks mean more favourable joint angles. The knees don't hit so high towards the chest, hip mobility is less of a challenge and the movement on a small track is "rounder" than with long cranks. All this leads to more stability in the saddle and, according to the unanimous opinion of all bike fitters, an aero position is easier to achieve.

Short cranks are in high demand

But when is short too short? In the series of tests carried out by the researchers, it can be seen that performance only suffers at extreme lengths well outside the usual spectrum - for example, at 125 or 200 millimetres instead of 170 millimetres. In contrast, very good performance was possible with cranks that were 150 millimetres short. However, this finding is based on a rather sparse data set with comparatively few test subjects and no top athletes. In general, cranks that are too long seem to be more harmful than cranks that are too short. Nevertheless, the researchers also emphasise that there is a proportionality between crank and leg length, i.e. what common sense tells you. It is obvious that a children's crank is not for a two-metre man. Accordingly, specialists such as Zinn Cycles from the USA, who also customise bikes for 2.30 tall basketball players, also produce extra-long cranks over 200 millimetres. However, the current world hour record was set by the long Filippo Ganna (1.93 metres) with 170 millimetre short cranks - "short" for his height. Ganna rode a length-adjustable Cratus crank from Wattshop with an adjustment range of 160 to 175 millimetres on his bike.

However, the short end of the spectrum often causes problems in practice. This is also served by specialists. Rotor offers a wide range of crank lengths, starting at 155 millimetres. US frame builder Matt Appleman from Minneapolis goes even further: his cranks, colourful and in small series, are well worth seeing and start at 135 millimetres. Some other frame builders also offer customised cranks, which is logical. Because if an XXS bike has a matching short crank, the bottom bracket can also be lower than normal, which improves handling and riding behaviour. A selection of suitable cranks is therefore definitely available - but the bikes are not equipped with the full range of cranks ex works. The fact that market leader Shimano limited itself to a few crank lengths for a long time was probably mainly for economic reasons. Production and warehousing are cheaper when there are fewer models in circulation. It is also easier for bike manufacturers if fewer sizes have to be kept in stock. But the market is responding to demand, and Shimano has expanded its range. For example, the (retrofit) range of 160 mm cranks has grown in recent years. 160 millimetre cranks can be ordered for Shimano's best-selling Ultegra components. However, as with narrow racing handlebars, which are also much more difficult to obtain than wide ones, shorter cranks are currently in greater demand - this can be seen in the range offered by online retailers, where the longest standard cranks (175 millimetres) make up the largest stock. Short cranks, on the other hand, often have longer delivery times.

Road bike crank length: Wrong standard?

If you work with figures on the size distribution of the population, you come to an interesting realisation: The traditionally offered and fitted cranks do not optimally match the size distribution of the population if you take 20.5 percent of the stride length as a criterion for the crank length, as is often suggested (see graphic below). The most commonly used crank length for men would then have to correspond more closely to that chosen by Tadej Pogacar. For men with an average height of 1.80 metres, the crank length distribution curve would then be at its widest at 165 millimetres. For women, the spectrum would be shifted by around ten millimetres and 155 millimetres would be the most common crank size. So has the industry been fitting the wrong cranks for years? Who knows, perhaps the best cyclist in the world is leading the way. In any case, it is conceivable that the range of crank lengths will shift downwards and expand with the knowledge gained from modern bike fitting. Women in particular would benefit from this, as they are more likely to have problems finding cranks that fit their bikes. Either way, a larger selection would be a step forward for all athletes.

The graphic shows a calculation of how the crank lengths should be distributed based on the size distribution of men in Germany. Assuming that 20.5 per cent of the stride length is the best first approximation for the crank length, most men would have to ride cranks 165 millimetres long, followed by 170 and 160 millimetres. 20 to 20.5 per cent of the crotch length is the most frequently cited key data for determining the crank length. For women, who are on average 14 centimetres shorter than men (average: 1.66 metres), the spectrum shifts by two sizes, so 155 millimetres would be the most common size - which is already outside the usual spectrum of crank lengths on offer.

The study situation on crank length on a road bike

There are relatively few studies on crank length. They come to the conclusion that moderate changes in crank length have no effect on the power output; with extremely short or long cranks outside the usual spectrum, the power output drops. Overall, the influence of crank length on performance is small. In short-term sprint tests, however, short cranks perform better than long ones. In a study, inexperienced riders performed better with short 145 mm cranks than with 175 mm cranks.

Should I change my crank length?

If you don't have any problems, you don't have to do anything. Shorter cranks reduce the strain on the knees, make it easier to adopt an aero position and can improve stability in the saddle. What change is noticeable? 2.5 millimetres is very little and the difference is not necessarily noticeable. It becomes relevant from 5 millimetres change in length, 10 millimetres can be felt very clearly. If in doubt, only trial and error will help. Cranks that are too long can be inefficient, but so can cranks that are too short. Repositioning cranks for a test is relatively easy if you have an alternative length to hand. Before varying the crank length, you can also try out other things to influence the movement: seat height, horizontal saddle position and cleat position on the shoes. If you move the saddle further forwards and set it higher, the hip angle also opens up. With shorter cranks, the seat height should be corrected upwards to achieve a similar leg extension.

Crank lengths for road bikes: Who offers what?

Traditionally, crank lengths of 170, 172.5 and 175 millimetres are common. They are fitted by most bike manufacturers. Shimano Ultegra groupset with 160, 165, 170, 172.5 and 175 millimetres. Dura-Ace also with 167.5 and 177.5 millimetres. SRAM Force and Red from 165 to 177.5 millimetres in 2.5 millimetre increments. Rotor from 155 millimetres.

Adjustable cranks are practical - such as those from Look, Wattshop (also for SRM) or WX Vario. Zinn Cycles, for example, manufactures made-to-measure cranks, while Appleman (pictured above), both in the USA, offers exotic lengths.

Long lever = more power?

Torque = force x lever arm. So doesn't a longer crank automatically produce more power? No, because power is speed-dependent and power = torque x angular velocity. Pedalling slower with a long crank can therefore generate exactly the same power as pedalling faster with a shorter crank. You tend to pedal more slowly with longer cranks because the foot is guided along a larger path. The long crank produces more torque during the initial acceleration. However, short cranks perform better in sprint tests.

Which cranks are suitable for whom?

Long cranks

• long legs
• low cadence
• Climbing

Short cranks

• short legs
• Aero position
• High cadence

Formula for the crank length

20.5 per cent of the inside leg length. There is no exact calculation method for the best crank length. The leg length is the best guide. 20 to 20.5 per cent of the inside leg length are often quoted values. A much coarser estimate is based on 10 per cent of body height, which tends to give higher values.