We know, there’s no such thing as a stupid question. But there are some questions you might not want to ask your local shop or riding buddies. AASQ is our weekly series where we get to the bottom of your questions – serious or otherwise. This one concerns all things crankset related. Hit the link at the bottom of the post to submit your own question!
Ever wondered what crankset material is most efficient for power transfer? Or what crank length you should really be running, despite what came stock on your new bike? We sent these reader questions and more to the experts at ROTOR, SRAM and Shimano. Thank you to Lori Barrett at ROTOR, Alex Rafferty at SRAM and Nick Murdick at SHIMANO for taking the time to respond.
How does crank length affect pedaling efficiency?
ROTOR: For most people, pedal stroke efficiency is more greatly impacted by an adjustable oval ring, like ROTOR’s Q Rings, than crank length. The ability to smooth out the application of power through the pedal stroke is easy to visualize on our INpower app, and modify with an adjustable oval ring.

Coming back to the question of crank length, however, it’s most important to note that it is a very individual puzzle, dependent upon the biomechanics of the rider, the geometry of the bike and goals for performance.
1. First and foremost, determining crank length is a matter of proper bike fit. Incorrect crank length can lead to biomechanical issues and injury, which cause reduced performance. Shorter cranks do reduce the upper angle when the foot is traveling over the top of the pedal stroke: a hyper-flexed knee places excessive shear forces on the patella and associated articular cartilage, often causing knee pain. Shorter crank arms relax this angle, thus reducing shear forces on the knee.
2. Additionally, a properly sized crank can help the rider spin a more effective cadence by reducing the overall distance the foot has to travel in one rotation. While it’s true that peak power is somewhat reduced (torque=force applied x lever arm length) there has been some research into the overall effect of the crank arm length by Jim Martin, Ph.D. of University of Utah (Determinants of Maximal Cycling Power: Crank Length, Pedaling Rate & Pedal Speed. Martin, JC1, Spirduso WW.). That research showed a minimal ~4% difference in overall power output across an entire range of crank lengths.

3. Lastly, a shorter arm will afford the rider a more aerodynamic position, resulting in a higher speed at a given power output. ROTOR offers crank options from 150mm to 175mm to accommodate most rider & bike set ups.
SRAM: I would suggest the best approach for this is factoring in the correct crank length for the user’s needs. Weighing up the rider’s height and also the desired pedal clearance with the ground.
A tall rider might prefer a 175mm crank whereas an average height rider may prefer 170mm or even 165mm. There is a notable difference on the amount of ground clearance on the shorter cranks that are better suited to bikes with lower BB’s.
SHIMANO: The short answer is that crank arm length doesn’t impact pedaling efficiency with the commercially available sizes on the market. Crank arm length selection does, however have other effects on riding, and it’s good to consider factors like back and knee pain, ground clearance, and center of gravity.
The recent trend in mountain biking is to use shorter cranks than the default selection of 175mm which began in the early days of mountain bikes. When using shorter cranks, your pedaling RPM will increase marginally to maintain the same power which is the consequence of reduced leverage.
Riders started using 170mm and shorter crank arms to improve ground clearance, especially because of the increase in pedal strikes from lower bottom bracket heights on modern MTBs. After all, pedaling won’t get you anywhere if your pedal hits a rock.









