Should I really be considering shorter crank arms?

I spend my Wednesdays doing bike fits out of our Denver location, and there is one question that comes up in almost every fit session lately. Should I go shorter on my cranks? Usually it is prompted by something a rider saw about Vingegaard or Pogacar racing on 150s or 165s, paired with a nagging feeling that their own 172.5s, which came stock on their bike and were never actually chosen, might not be right for them.

Here is the short version of what I tell them in the fit room. The fear of losing power on shorter cranks is not supported by the data, and crank length is far more useful as a tool for solving hip and back issues than it is a performance lever.

Nobody actually chose their crank length

This is the part that surprises people most. Almost nobody riding a 172.5 crank chose it because it was tested and found to be optimal for their body. It is simply what the manufacturer speced on the complete bike. A 5'6" rider and a 6'2" rider often end up on the same length purely because of what size frame they bought, not because anyone measured their hips, their femur length, or their mobility.

Once you understand that the industry standard was never really a standard chosen for you specifically, the question shifts. Not "will changing hurt my power," but "what length actually fits my body."

What the research says about power

The lab work on this, most of it out of Jim Martin's group at the University of Utah, is fairly conclusive. Trained cyclists tested across a 50mm range of crank lengths, from 145mm to 195mm, showed no significant difference in maximum power output. When researchers zoomed in on the comparison most relevant to a rider considering a modest change, say from 170mm down to 145mm, the difference in peak power was under 1%.

The mechanism is fairly intuitive once you see it. A shorter crank puts less demand on hip and knee flexion at the top of the pedal stroke. Less flexion means your muscles are working from a stronger position in their range, similar to how a partial squat lets you move more weight than a deep squat. That mechanical advantage largely offsets the shorter lever length. Torque does not scale linearly with crank length the way people assume, because the body is not a fixed machine, it adapts its leverage as the joint angles change.

What actually changes when you go shorter

If power is roughly a wash, what is the actual reason to consider a shorter crank? In the fit studio, it usually comes down to one of a few things.

Hip range of motion. A long crank asks for more hip flexion at the top of the stroke. If a rider's hip cannot access that range cleanly, something has to give, and it is usually the lumbar spine rounding to fake the motion or the pelvis rocking with each pedal stroke. I see this constantly in riders who also deal with low back tightness off the bike. Shortening the crank reduces the flexion demand and often resolves the discomfort without touching anything else about the fit.

Anterior hip impingement. Riders with any bony or soft tissue impingement at the front of the hip feel it acutely every single pedal stroke on a long crank. This is one of the fastest fixes available in a fit session. Drop the crank length and the impingement symptom often disappears immediately, on the spot, during the fitting.

Position and aerodynamics. A shorter crank allows a lower front end without the knee driving into the chest at the top of the stroke. For anyone chasing a more aggressive position, whether for racing or just efficiency on longer rides, this matters more than most riders realize.

Technical terrain clearance. For the mountain bikers and gravel riders I see in Denver, pedal strikes on rock gardens and technical climbs are a real, practical problem. Shorter cranks mean more ground clearance, full stop.

The adaptation happens faster than people expect

The other objection I hear constantly is some version of "I have been on 172.5s my whole life, I will never adjust." In the actual lab studies, riders were tested across a huge range of crank lengths in a single session with only a short warm up on each length, and performance held up. Riders reported their own bikes felt strange for the first mile after the test, then normal again. That is how quickly the nervous system recalibrates.

Give a new length two weeks of regular riding and it stops feeling like a change at all.

What I look at during a fit

When someone comes in wondering about crank length, I am not guessing. I look at hip flexion and internal rotation range off the bike, watch how the pelvis and lumbar spine behave through the pedal stroke on the trainer, and check for any pinching or impingement sensation at various crank lengths before we commit to anything. For most riders coming off a stock 172.5 or 175, especially anyone under 5'10" or dealing with any hip or low back symptoms on the bike, there is a real chance a shorter length solves problems they have been quietly tolerating for years.

If you are curious whether your crank length is actually right for you, or if you have been dealing with hip or low back discomfort that shows up specifically on the bike, that is exactly the kind of thing we sort out in a fit.