Does Crank Arm Length Actually Matter? New Research Says the Answer Is More Complicated Than You Think

Walk into any bike fit studio and mention crank arm length and you'll provoke one of two reactions: a long, passionate explanation about hip mobility, leg length ratios, and biomechanical efficiency, or a polite shrug and a suggestion that you stick with whatever came on the bike. Both responses have a problem: until recently, the research underpinning either position was thin.

A study published in the Journal of Science and Cycling in 2026 set out to fix that, using augmented reality environments to isolate the effects of crank arm length on cycling performance metrics in a controlled setting. The results are worth knowing — whether you're choosing a first set of cranks or questioning whether your current 172.5 mm arms are leaving watts on the table.

What the Research Actually Tested

The study's methodological innovation was its use of augmented reality to standardise variables that confound real-world crank testing. In traditional crank length studies, differences in saddle height, rider position, and pedalling mechanics can introduce noise that makes it difficult to isolate the crank's specific contribution to power output, efficiency, or comfort. The AR environment allowed researchers to adjust the virtual ride conditions while keeping riders' positional inputs constant.

The metrics tracked included power output at submaximal and maximal intensities, gross mechanical efficiency (how effectively a rider converts metabolic energy into mechanical work), cadence preferences at set power targets, and comfort-related variables assessed through rider-reported scales. The sample included endurance-trained adults with experience in cycling — not purely recreational riders, but not WorldTour professionals either.

The Findings: Smaller Differences Than Expected

The headline result: across the population of trained cyclists tested, differences in crank arm length — within the standard range of 165 mm to 175 mm — produced smaller performance effects than the existing literature might suggest. Power output at submaximal intensities was not significantly different across crank lengths when riders were given time to adapt. Gross mechanical efficiency showed marginal variation, with the direction of effect depending on individual biomechanics rather than following a consistent pattern.

What did vary meaningfully was comfort and hip mechanics at the top of the pedal stroke. Riders with limited hip flexion range — a common constraint, particularly in masters cyclists and those with desk-job postures — showed measurable improvements in comfort metrics on shorter cranks. Shorter arms reduced the degree of hip flexion required at 12 o'clock in the pedal stroke, which in turn allowed a more relaxed and sustainable position over longer durations.

The implication is important: crank length selection for most riders is less a performance variable and more a fit and comfort variable — and in cycling, comfort over duration is itself a performance variable.

The Cadence Relationship

One area where crank length did show consistent effects was cadence. Shorter cranks — 165 mm and 167.5 mm — allowed riders to sustain higher cadences at equivalent power outputs compared to 172.5 mm and 175 mm cranks. The mechanism is straightforward: shorter cranks reduce the rotational inertia of the pedalling system, making it physically easier to spin at high RPM.

For riders who train around specific power zones and want to maintain cadence targets — particularly during threshold and VO2max work — this is a meaningful consideration. If your cadence naturally drops below your target at intensity and you're on 175 mm cranks, experimenting with 170 mm or shorter is a low-cost intervention worth testing before spending money on power data analysis.

The caveat is adaptation time. Most studies, including this one, found that riders needed several weeks to adapt to a new crank length before performance metrics stabilised. Switching cranks the week before your A-event is not the strategy the research supports.

What Bike Fitters Are Actually Doing

The science aligns with what progressive bike fitters have moved toward over the past several years. The default crank length of 172.5 mm — standard on most production bikes — was set decades ago for average proportions and is increasingly recognised as suboptimal for a significant proportion of riders.

Fitters now commonly use femur length (not total leg length) and hip mobility assessments to guide crank length recommendations. Riders with shorter femurs, limited hip flexion, or a history of knee pain at the front of the joint are frequently moved to 165–170 mm cranks with positive results. Riders with longer femurs and good hip mobility may genuinely perform better on 172.5 mm or longer, but the performance gains over shorter cranks are modest — the comfort argument for shorter cranks typically remains.

The practical takeaway: if you've never questioned the crank length that came with your bike, you may be leaving comfort, cadence consistency, and potentially some power on the table.

What This Means for Your Riding

Crank arm length is a fit variable first, a performance variable second. If you experience anterior knee pain, struggle to maintain target cadence at intensity, or feel constrained at the top of your pedal stroke, your cranks are worth reviewing before your next training block. The process is straightforward: measure your femur length, assess your hip flexion range, and consult a qualified bike fitter who uses objective measurements rather than rules of thumb. The Journal of Science and Cycling research gives that conversation a solid evidence base. And if you're riding 175 mm cranks that came standard on your bike, there's a reasonable chance you'd benefit from trying something shorter.