Many riders focus a lot on handlebar height and saddle position when setting up their bikes, but don't pay enough attention to crank length. When you buy a factory-built bike, the crank length is usually chosen based on the frame size, but that doesn’t always mean it’s the best fit for you. If it's not right, it can cause discomfort and make your performance less efficient. So, it's important to think about it carefully.

Here, we'll explain why choosing the right crank length is important and go over the advantages and disadvantages of different crank length calculators.

Crank length is generally chosen based on leg length, but other factors also matter and will be discussed below. Bike designs usually assume an average height distribution, but this makes big assumptions about leg-to-height proportions, which can vary a lot (in our clinic, from 43.2% to 50.1%). People also have a wide range of leg lengths (67.5 cm to 94 cm in our clinic), while the crank lengths that are commonly available cover only a small part of that range.

The standard crank lengths are typically 165mm for shorter cyclists and 175mm for taller ones, with most people using 170mm or 172.5mm cranks. Major brands usually offer cranks in 2.5mm steps, ranging from 165mm to 175mm.

Bikes come in many different frame sizes for adults, usually from 44 cm to 61 cm. But there are far fewer crank size options. This means many bikes don’t fit riders properly, which can be a bigger problem for women. Let’s look at the science, the common myths, and practical tips for choosing the right crank length.

The importance of calculating the right crank length for you

People have often thought that a longer crank gives more leverage, which should produce more power. But recent research suggests this might not be true.

Power comes from a combination of torque (how hard you push) and cadence (how fast you pedal). The length of the crank only affects torque. Longer cranks give more torque for the same pedal force, but they usually make your pedaling slower because the pedals travel in a bigger circle. These two effects balance each other out, so overall power usually stays the same.

An exception to this is when starting from a standstill with a fixed gear over a short distance (100-200m), like in a track start. Longer cranks allow the rider to reach higher speeds than shorter cranks.

On a geared bike, the difference is mostly gone when riding on the road because you can shift to an easier gear, especially while sitting. You might notice a small difference in high-effort situations, like starting from a stop at traffic lights or climbing steep hills while standing, but these moments are rare compared to normal riding.

Choosing the right crank isn’t about tradition—it’s about fitting your body and how you move.

Is there an optimal crank length?

A common idea is that there might not be a single “right” crank length, but there can be a wrong one. Choosing a shorter crank is usually safer. A crank that’s too long can cause problems, especially at the top of the pedal stroke, while a shorter crank doesn’t reduce performance.

A crank that's too long can make the hip and knee joints bend too much at the top of the pedal stroke, putting pressure on them and causing pain. It might also lead to riders adjusting their movements in ways that can cause other problems later, like rocking their pelvis or flaring their knees outward.

This problem gets worse if the hip cannot bend enough, either because of general stiffness or conditions like femoral acetabular hip impingement or hip osteoarthritis. Not only can this cause hip pain, but if the hip cannot stay in its normal range at the top of the pedal stroke, the pelvis often tilts backward to compensate, which can lead to too much bending in the lower back.

Pelvic rocking can cause lower back pain, saddle sores, and reduce power because of pelvic instability. If the cranks are too long for the rider, they might subconsciously shift their hip or pelvis to get their leg over the top of the pedal stroke.

Cranks that are too long can make it hard to pedal quickly. They can cause your knees to hit your chest when you lean forward, and make breathing harder.

The benefits of shorter cranks

Shorter cranks can make a bike more aerodynamic, which is why they are often used on time trial bikes. For example, before his 2015 hour record attempt, Bradley Wiggins (who is 190 cm tall) switched from 177.5 mm cranks to 170 mm ones to improve aerodynamics. Shorter cranks let the saddle be higher, which opens up the hip angle at the top of the pedal stroke and allows the handlebars to be lower, creating a more aggressive riding position.

Shorter cranks push your thighs away from your stomach at the top of the pedal stroke, making it more comfortable and easier to breathe. They can also help with pain or injuries in the hips, knees, and lower back by reducing stress on these joints and improving movement.

Shorter cranks can improve pedal clearance and reduce the chance of pedal strike, which is helpful in crit racing or mountain biking (to avoid hitting rocks and roots). They also reduce toe overlap, especially on smaller frames.

Crank length calculator

A good approach is: use 155mm or 165mm cranks for most riders.
Riders at the smaller or larger end of the spectrum can use 145mm or 175mm cranks.
Only a few outliers might need 135mm or 175mm.

Small changes of 2.5mm aren’t worth switching cranksets, since cranks are expensive. A change of at least 5mm, and ideally 10mm, has a bigger effect on your hip and knee angles.

Crank length is often thought to depend on leg length, but that's not always the case. Even if two people have the same inseam, their ideal crank length could be different based on other factors. A rider with better flexibility and fewer injuries might be able to handle longer cranks without any problems.

Crank length should be chosen based on the rider’s body and needs, including flexibility, joint range, strength, past injuries, type of riding, cycling goals, and personal preference. If you feel discomfort, pain, or have an injury, adjusting crank length should be part of a full bike fit.

If you're looking to boost your cycling performance and speed through better aerodynamics, shorter cranks might help. They're also useful for smoothing out your pedal stroke and getting rid of dead spots, especially if you have limited joint range of motion.

Once you’ve chosen a crank length, the next step is testing whether it actually improves your performance. This is where a power meter becomes extremely useful.

Devices like the Coospo S10 Spider Power Meter allow you to track real-time power output, cadence, and efficiency, helping you compare different crank setups objectively. With dual connectivity (ANT+ and Bluetooth) and accessible pricing, it makes structured training and bike fitting more data-driven and practical. By analyzing your power consistency, cadence, and comfort across rides, you can confirm whether your crank length choice truly works for your body.