The Question Everyone Started Asking This Year
Somebody in your group ride has gone to 165mm cranks. They read that the pros are doing it, they swapped, and now they will tell you about it on every climb up to Tanjung Rambutan.
Crank length is the fit conversation of 2026, and it is unusual among cycling trends because there is a decent pile of evidence sitting underneath it. The evidence just does not say what most riders think it says.
The short version: nobody has been able to show that crank length changes your power. What it reliably changes is how much your hip and knee have to bend, and that is a fit question, not a performance one.
Five Studies, No Power Difference
This is the part worth understanding before you spend money.
The widest test ever run. Sixteen trained cyclists produced maximal power on cranks of 120, 145, 170, 195 and 220mm. That is a 100mm spread, far beyond anything sold on a road bike. Maximum power ranged from 1149 W on the 220mm cranks to 1194 W on the 145mm cranks, a difference of under 4% across the entire range. The 145 and 170mm cranks beat the 120 and 220mm cranks, and that was the only significant separation. The authors concluded that using standard 170mm cranks “should not substantially compromise maximum power in most adults.”
Broken down joint by joint. A later study put fifteen trained cyclists on 150, 165, 170, 175 and 190mm cranks and calculated how much power each of the hip, knee and ankle contributed. Once pedalling rate was optimised, crank length had no significant effect on joint-specific power anywhere in the leg.
At the sizes you would actually buy. Twelve amateur road cyclists rode at 150, 200 and 250 W on their preferred cranks (172.5 to 175mm) and at plus and minus 5mm. Heart rate was 144, 145 and 145 bpm. Gross efficiency was 20.4%, 20.1% and 20.3%. Nothing.
Tested again in 2025. Twenty-eight trained cyclists rode 165, 170 and 175mm in a randomised, single-blind crossover. No difference in oxygen cost, cycling economy, six-second sprint peak power, sprint average power, cadence or heart rate.
And again in 2026. Fourteen amateur cyclists rode five crank lengths with full three-dimensional motion capture. Mean power output: 199.1 W, unchanged across every length.
Five studies, four decades, different labs, different protocols, sprint and submaximal. None of them found a power cost. If you are considering shorter cranks because you expect to go faster, the evidence does not support you. If you are avoiding shorter cranks because you expect to lose watts, the evidence does not support that either. That is the useful finding: crank length is close to free, in both directions.
What Actually Changes
If power is unaffected, something else must be, and this is where crank length earns its place in a fit.
The 2026 motion-capture study found that shorter cranks produced:
- Significant decreases in knee flexion and hip flexion
- Increased anterior pelvic tilt
- Less pelvic obliquity, less pelvic rotation, less hip abduction and less knee rotation
The 2017 study found the same relationship from the other direction: a longer crank increased the maximum flexion and range of motion at the hip and knee by 1.8 to 3.4 degrees, while leaving the ankle alone.
The mechanism is simple once you see it. Shorten the crank by 5mm and the pedal now sits 5mm higher at the bottom of the stroke, so you raise the saddle 5mm to keep the same leg extension. At the top of the stroke the pedal is 5mm lower than it was and your saddle is 5mm higher, so your knee comes up about 10mm less than before. The tight end of the pedal stroke opens up. The long end stays where it was.
Everything else follows from that. A hip that has to close less at the top can sit in more forward pelvic rotation. A pelvis that is not being pushed backwards by a jammed hip angle rocks and twists less. The authors of the 2026 study concluded that shorter cranks “could serve as an effective bike manipulation to reduce the risk of overuse injury” and “could limit stress on the lumbar spine.”
There is one more finding worth having. In the 2025 study of 28 riders, perceived exertion at the same submaximal workload was significantly lower on 165mm and 170mm cranks than on 175mm, with no difference between 165 and 170. Same oxygen cost, same power, same heart rate, but the shorter cranks felt easier. For a rider spending four hours on the bike, how it feels is not a small thing.
Why This Connects To Knee Pain
We wrote in Knee Pain After Cycling that the pattern distinguishing cyclists with knee pain from cyclists without it is not how far the knee bends. It is how the knee tracks, viewed from the front, and specifically whether it falls inward under load.
Look again at what shorter cranks did in the 2026 study: less knee rotation, less hip abduction, less pelvic obliquity. Less out-of-plane movement is exactly the direction the knee pain research points toward.
That is a mechanistic argument, not proof. Nobody has run a trial putting riders with knee pain on shorter cranks and following them for a year. What we have is a plausible link between two separate findings, which is worth acting on when the intervention costs you no power, and is not worth overselling.
The Number Most People Quote, And What It Means
You will see it claimed that your crank should be 20% of your leg length. That figure is real, and it comes from the 120 to 220mm study: the optimal crank length for maximal power was 20% of leg length, or 41% of tibia length.
Two things to know before you reach for a tape measure.
First, it was derived from maximal sprint power on a laboratory ergometer, which is not what you do on a four-hour ride. Second, and more important, the crank-to-leg-length ratio only explained 20.5% of the variation in maximum power between riders. Roughly four fifths of the difference was something else. It is a real relationship, and it is a weak one.
For most Malaysian riders the practical point sits elsewhere anyway. The bike industry has historically shipped nearly everything with 170 or 172.5mm cranks regardless of who is buying it. A rider at 160cm and a rider at 185cm get handed the same lever. If you are on the shorter end and you have never questioned your cranks, you are riding a length that was chosen for someone else.
The Honest Caveat
A 2024 systematic review screened 16,578 studies on bike position, analysed 47 of them, and rated study quality as none “good”, five “fair” and 33 “poor”. Its verdict on our topic was direct: there are no clear recommendations for crank length, handlebar height, Q factor or cleat position.
That is the state of the field. The studies above are consistent about power and consistent about joint angles, but they are small (12 to 28 riders), almost entirely male, acute rather than long term, and none of them followed riders to see whether anybody actually got injured less. Anyone telling you that shorter cranks will fix your knee is going beyond the evidence.
What the evidence does support is narrower and still useful: shortening your cranks reduces hip and knee flexion, opens your hip angle, reduces out-of-plane movement at the knee and pelvis, and costs you nothing measurable in power.
Who Should Actually Consider It
Based on what the studies changed rather than what they did not:
- Riders with limited hip mobility, whose knee comes up very high at the top of the stroke and whose back rounds to make room for it.
- Riders with anterior knee pain, given the reduction in knee flexion and knee rotation.
- Riders on the smaller end of the size range who are on stock 172.5mm cranks purely because that is what the bike came with.
- Riders who want a lower front end but keep running out of hip angle before they get there. Shorter cranks buy you room that stem spacers cannot.
- Riders whose lower back complains on long rides, given the pelvic tilt finding.
And who should not bother: if you are comfortable, your knees are quiet, and you can hold your position for four hours, crank length is not your problem. Chasing it will not give you watts, because there are no watts there to find.
What It Costs You To Change
Not much, but not nothing:
- You must raise your saddle by the same amount you shorten the crank. Skip this and you have simply lowered your saddle, which is the one change most likely to cause the anterior knee pain you were trying to avoid.
- Your saddle-to-bar drop increases by that same amount unless you also raise the bars. For most riders wanting a more open hip that is the point, but it is a real change to your reach and it should be measured.
- Your cadence will drift slightly upward. In the maximal-power study, optimal pedalling rate fell from 136 rpm on 120mm cranks to 110 rpm on 220mm cranks. Shorter cranks favour spinning. If you are a habitual grinder this takes a few rides to settle.
- Cranks are not cheap, and on many modern bikes the crankset is bound up with the power meter and the chainrings.
This is why crank length is a fit conversation. Changing it without moving the saddle to match converts a neutral change into a bad one, and we covered that chain of consequences in 5 Hidden Bike Fit Mistakes New Cyclists Make.
Before You Buy Anything
Try this first, because it costs nothing. Ride a session deliberately at a higher cadence in an easier gear, and pay attention to whether the top of the pedal stroke is where your discomfort lives. If your complaint is a jammed, cramped feeling at the top, or a back that rounds to make room for your knee, shorter cranks address exactly that. If your complaint is at the bottom of the stroke, or is a saddle problem, or is one-sided, crank length is not your answer and a shorter crank will just move things around.
Then get the position measured before spending money on parts, because the same open hip angle can often be found in saddle fore-aft and bar height for free. That argument is the one we made in Professional Bike Fit vs YouTube DIY.
The Short Version
Crank length does not change your power. It changes how much your hip and knee have to bend, how your pelvis sits, and how much your knee wanders out of line, and it does all of that at no measurable performance cost. That makes it one of the cheapest levers in a bike fit for a rider who is running out of hip angle, and a complete waste of money for a rider who is already comfortable.
The pros did not go short to get faster. They went short to get lower.
References
- Martin, J. C., & Spirduso, W. W. (2001). Determinants of maximal cycling power: crank length, pedaling rate and pedal speed. European Journal of Applied Physiology, 84(5), 413-418. PubMed: 11417428. The 120 to 220mm range, the 1149 to 1194 W figures, optimal pedalling rates and the 20% of leg length ratio.
- Barratt, P. R., Korff, T., Elmer, S. J., & Martin, J. C. (2011). Effect of crank length on joint-specific power during maximal cycling. Medicine & Science in Sports & Exercise, 43(9), 1689-1697. PubMed: 21311357. No effect on hip, knee or ankle joint-specific power.
- Ferrer-Roca, V., Rivero-Palomo, V., Ogueta-Alday, A., Rodríguez-Marroyo, J. A., & García-López, J. (2017). Acute effects of small changes in crank length on gross efficiency and pedalling technique during submaximal cycling. Journal of Sports Sciences, 35(14), 1328-1335. PubMed: 27484153. The heart rate and gross efficiency figures, and the 1.8 to 3.4 degree change in hip and knee range of motion.
- Li, J., Wang, Q., Zhang, Y., et al. (2025). Effects of crank length on cycling efficiency, sprint performance, and perceived fatigue in high-level amateur road cyclists. Journal of Exercise Science & Fitness, 23(3), 175-180. PubMed: 40342376. The 28-rider crossover and the perceived exertion difference between 165, 170 and 175mm.
- Reynolds, S., Chidley, J., Briley, S., & Outram, T. (2026). The impact of minor crank length adjustments on lower body cycling kinematics. Sports Biomechanics, 25(3), 454-467. PubMed: 40464620. Unchanged power output, reduced hip and knee flexion, increased anterior pelvic tilt and reduced out-of-plane motion.
- Husband, S. P., Wainwright, B., Wilson, F., et al. (2024). Cycling position optimisation: a systematic review of the impact of positional changes on biomechanical and physiological factors in cycling. Journal of Sports Sciences, 42(15), 1477-1490. PubMed: 39285616. The study quality ratings and the absence of clear crank length recommendations.
Not Sure If Your Cranks Are The Problem?
Crank length is worth changing for a specific reason and worth ignoring otherwise. The way to tell the difference is to look at where your hip and knee actually run out of room, which is what a fit measures.
Chat with our AI bike fit expert on WhatsApp for a free assessment. Tell us your height, your current crank length, and where the discomfort sits in the pedal stroke.