As non-inflammatory as that question may seem, the issue of crank length on bikes has become one of the more heated discussions in bike fit and set-up recently. For many years, the basic crank lengths that would be supplied on bikes typically were 170 mm, 172.5 mm and 175 mm. The rider’s height would indicate the best crank length to choose – the taller you were, the longer the crank.
In fact, that is still considered a good rule of thumb to follow. Most component manufacturers will tell you that your crank length should correspond to your height, and in particular, your leg length. But as with anything to do with bike fit, there are a huge number of variables that impact crank length, and in turn will be impacted by a change in crank length.
What are common crank lengths?
Though the differences in crank lengths might sound miniscule to the point of being insignificant, the change of 2.5 mm in length can have a radical effect on your comfort and even your performance. Though it can be difficult to find cranks smaller than 165 mm or larger than 175 mm, they can range from 155 mm up to 220 mm. That being said, not all component manufacturers will offer the full range of lengths for their cranks.
The most typical crank lengths are 160, 165, 167.5, 170, 172.5, 175, 177.5, and 180 mm. Which of these you choose will have a lot to do with your ambitions and riding style in addition to your physical size. It’s hard to find a general consensus among bike fit experts about what is the best crank length, but anecdotal evidence indicates 170 mm appears to be the crank sweet spot for most people. And that makes sense looking at the list of crank lengths since it falls right in the middle of commonly available lengths.
Best crank arm length for road bikes
One of the more recent trends in bike fits is for riders, even very tall riders, to choose to have short crank arms. It’s well known that all-round phenomenon Tadej Pogačar has been riding with 165 mm crank arms and even perhaps testing how 160 mm cranks work for him. For a rider who is listed on Pro Cycling Stats as being 1.76 m or about 5’8”, that still seems to be quite short. Just 10 years ago, he would have likely been riding 170 or perhaps 172.5 mm crank arms.
The trend towards shorter cranks is interesting since for many years, the conventional wisdom claimed that one should ride with the longest crank length that their body size could accommodate since a longer crank allows for greater torque thanks to the extended leverage. And indeed, some riders still today claim that they prefer longer cranks when climbing steep hills to benefit from that added torque.
Today the argument for shorter cranks has to do with the flip side of that same coin. Shorter cranks often smooth out pedaling styles to help you spin more easily. Perhaps more importantly from a professional’s point of view is that shorter cranks allow you to sit in a more aerodynamic position since you will be able to drop your hips and move your front end closer to the bars. The shorter cranks will also make it easier for you to pedal through corners, since you’ll have greater ground clearance.
How to measure your best bike crank length
Since most of us are more interested in comfort on the bike and are not Pogačars or Pidcocks looking for every possible performance advantage in our cycling, the most important issue is whether you are suffering from chronic on-the-bike knee, hip pain and/ lower back pain. And even then, there are so many other potential culprits causing the pain, checking your crank length is only one of a list of things to check.
A proper bike fit by a professional will be the best solution, since that way you will have the chance to find the right saddle height, stem length, handlebar width, and crank length, among other things. Of course, a certain amount of trial and error might be required, which makes the changing of your crank length potentially an expensive experiment.
If you have bought your bike as a complete build with components and component sizes decided by the manufacturer, you might be in a position where you will eventually want to change out all these types of parts so you can dial in the perfect bike fit. That’s one reason that we do advocate and facilitate buying a custom bike so you can get all these parts right the first time.
Conclusion - Don’t just focus on the cranks
When you do finally decide that you want to choose a different crank length, keep in mind that you will need to adjust your saddle height by the same amount, raising it if you get a shorter crank, and lowering it if you opt for a longer crank. Similarly, the crank change will impact how far forward you are able to rotate your hips, impacting your reach to the bars. That might mean you will want to revisit your stem length as well.
As with all things to do with getting the right fit on your bike, the question of the best crank arm length is highly subjective. You should resist trends that pro riders follow since their needs are different from yours and changing out cranks is free and easy for them. Assuming you are starting with a reasonably sized crank length, in other words, you are not 5’2” and riding a 177.5 mm crank, then changing your crank might not be necessary. You should listen to your body: do you have chronic knee or hip pain? If so, then you should visit a professional bike fitter and together decide whether you want to experiment with changing your crank length.
And if you are planning to buy a bike that you personalize for yourself, use our bike fitting calculator to create the perfect bike for you!
