The Crank Length Argument

In the last three to four years, there has been a trend among not only top-level athletes but also industry leaders towards the use of shorter cranks. Many cycling outlets have reported on how shorter cranks have so many benefits for all types of riders. Tadej Pogačar, who is 5'9", won this year's Tour De France and Giro D'Italia on 165mm cranks. Tom Pidcock, the 5'7" British cycling multi-discipline star and Paris Olympic mountain bike champion, also runs 165mm cranks. This got me thinking. Being 6’1”, and long-legged, the thought of “this doesn't apply to me, my legs are too lanky” went through my head every time I read about it. From when I first started bike racing as a wee lad, to the last stock bike I bought (last year), every bike I had owned was equipped with 175mm cranks. Riding a size large, this was the standard. I never knew anything different. I never really had any issues. Then I read how Ineos rider, Filippo Ganna is 6'4 and rides 170mm cranks. This convinced me to give it a shot. Intrigued by the likes of many pros, and inspired by Tadej Pogačar's current domination with 165mm cranks in the tour, I set out to go shorter myself. 

Up until last year, I had never owned a road bike. Sure, I did some gravel occasionally, but mountain biking was my domain.  Wanting to mix it up, I stepped out of my comfort zone and bought my first road bike, a BMC Teammachine. After riding all of 2023 on that BMC, road bike became something I thoroughly enjoy.  My 58cm BMC came, as expected, with 175mm crankarms. Being on the staff at the shop, I have the opportunity to ride a lot of bikes so I decided to purchase an Enve Melee this spring and had a chance to build it from the "frame-up". This allowed me to be more specific on the individual components including choosing 170mm cranks. Now with months of power meter data and 175 vs 170 cranks, the numbers don't lie, and neither do my knees ;) 

Why try shorter cranks?

The virtues of running short cranks include increased comfort, better aerodynamics and the ability to produce more power. The physics don't lie. Power is a function of force on the pedals and cadence, so if you can maintain the force, but increase the cadence - you make more power. only a couple of weeks of riding, I already enjoyed the shorter cranks more, not even looking at the numbers. I felt less wear over long rides, and less knee pain that I sometimes would get climbing at the end of a long week. I also noticed that I could breathe a little better with my more rolled-over position on the bike than I had been able to previously due to less hip pinching. Was there a placebo effect? I am always dubious of whether what I am feeling is placebo or not so I tracked the numbers. 

The sample group for this little experiment is rides exclusively between 60-150 miles and 16 rides for both. Plus these rides are taken in Zone 2 by heart rate and power by the numbers, here's how the rides break down… 

As expected, the shorter crank increased my cadence.  While it was only an increase of 1.5 RPMs, this is a step in the right direction. Think about minimizing knee movement as maximizing efficiency. For every full rotation of the cranks, both knees have to bend at the top of the pedal stroke, moving (depending on the person's saddle height) around 90-110° at the knee. Shorter cranks make for a less severe angle on the knee at the top of every pedal stroke. A less severe angle should help towards more knee health in theory. In some cases, cyclists also have reported less back pain with shorter cranks.  Shorter cranks improve hip mobility by opening up the front of the hips, reducing tightness and improving comfort.  

How much are you saving? 

Let's think about this as a distance saved as the circle the foot moves in a full-pedal revolution. With some basic geometry, a 175mm crank arm makes for just under 1100mm of travel during a single pedal stroke. With a 170mm crank, the distance is just over 1068. That's 32mm less movement per leg, per pedal stroke.

So 32mm of less movement for a 5mm shorter crank. 32mm is not a lot, but now imagine that same 32mm of saved movement 73 times a minute. Then consider the cumulative impact on a five-hour ride.  While I am a fairly low cadence rider, if your average cadence is 80, 85, 90 or above, it's going to matter even more. If my average cadence is 73rpm, that means I am not just saving 32 mm of movement, but over the course of one hour, I am saving 140 meters of movement. If the rider's cadence is closer to 80rpm, saving nearly 154 meters of movement per hour. This sounds like a lot, but lets hammer it in more.  These numbers are for only one leg.  Think about how much you ride in a year. Your knees, hips, and back might thank you.  Your cycling performance might also!

What size should you be running? 

There is a lot of support for shorter cranks from bike-fitters and physiologists. It is not the easiest thing to "try" because it requires a new set of cranks. For my test, I compared 175mm cranks to the 170mm.  As I am pretty tall, 170mm would be considered on the shorter side of cranks for me. Shorter cranks will help with how high the knees come towards a riders chest. SRAM makes the Force carbon crank as short as 165mm. For a rough guide, look at 165mm cranks for people from >5’-5’5”, 167.5 for 5’6”-5’10”, 170mm for 5’10”-6’1”, 172.5 for 6’2”-6’4”, 175mm for 6’4” +. You can go lower and higher than this according to personal preference. 

Other questions? 

There's a lot to think about when it comes to cranks, but the number of great options out there makes it fairly easy to implement. For those who want to feel like Tadej and run shorter cranks, let us know if we can answer any questions or help with further recommendations. Give us a ring at the shop, drop us an email, or reach out on the chat and we'll help set you up!