By Rick Schultz
In about 15 minutes, GCN Tech did a pretty good job in this video discussing a complicated subject. Still, what was discussed is just the tip of the iceberg, and I’m afraid many cyclists will listen to them, invest in shorter-cranks (vs. “right-sized” crank arms as I call them – they become right-sized after the bike fit) without making other adjustments and end up worse for it.
The main question is how long should you choose? Their fitter said he once saw a 155mm (more than likely a ROTOR ALDHU), but we all know other companies make shorter. If you need a custom 155mm road bike crank with a MTB Q-Factor, those are made as well. You need a 153mm custom crankset, we can get those.
Pedaling a bicycle crank is an engineering four-bar linkage system where you are basically converting linear motion (legs going up and down) into angular motion (crankset rotating around the center of its spindle). Complicating this is the asymmetric human. Not only are we different from left to right but some people have longer torsos than legs while others have longer legs than torsos.
More complications exist with long femurs with short tibias vs short femurs with long tibias. Each of these place the cyclist in a different position on the bicycle. Oh, I forgot to mention range-of-motion limitations, tight muscles, weak muscles, mobility and impingement issues.
For example, I have a good friend that is 6’3” (190.5cm) tall, around 435w FTP, and California State ITT Cat 2 Champion. What crank length do you think he uses? (The answer appears later in this article).
The main problem with crank lengths was that years ago, there were several “experts” who published crank length formulas based on “best guesses” (that’s the only thing I can think of to explain their numbers). My own experience, after about three years of racing, is that I started getting knee pain. The thought back in the 80s was the longer the crank the better the leverage and the faster you can go. So racing bikes came recommended with Campagnolo Super Record 175mm cranks (they even made 177.5 and 180mm at the time). Then why was I getting knee pain?
Doing a little research, I found several bicycle crank-length calculators. Plugging in my specifics, one calculator recommended that I use 220mm crank arms! What?!?! If I am getting knee pain using 175mm cranks, how would 220mm help?
So, I raised my saddle which helped a little (again, back in the ‘80s the thought was LONG stems and LOW saddle heights). Raising my saddle further, I was now having trouble reaching the pedals without rocking my hips, so the saddle height was maxed out.
Around this time, Shimano offered a 165mm and 170mm Dura-Ace 7400. I picked up this groupset, but specified 170mm. Wow, this felt much better. Several years later, all of the manufacturers started coming out with 172.5mm. Why, a 172.5? If you ask the component manufacturers, the best answer you will get is “it’s between a 175 (which is too long for most) and a 170 (which is too short for most) so we split the difference.” That was bike fitting in the ‘90s.
Years later, I got heavy into bike fitting – or so I thought. I took several bike fitting classes, and I picked it up pretty fast, until my daughter (at the time undergrad in kinesiology, now a doctor in physical therapy), came to me and asked, “Dad, do you want to be a good bike fitter?” I answered, “Yes.” She then said, “You need to learn biomechanics, anatomy and kinesiology.” Wow, this made sense, so I went back to school and took some classes. It was eye-opening how much I didn’t know about how to fit an asymmetric machine (human) onto a symmetric machine (bicycle).
So again, I started looking into crank lengths. I became the fitter that everyone came to, to fix their knee-pain. I eventually took data from 2,500 of my fitting clients and developed my own crank length formulas, which still work to this day. We go through these in detail in my bike fitting classes.
Lately, I have been looking into mid-foot cleat placement (Mid-Foot Cycling mid-foot-cycling.com), and I have also been using the ERGO3’s for a year now. I have also recommended them to many cyclists with Calf/Achilles/Ankle mobility and foot pain issues. The correct insoles (such as Icebug insoles) are also important, but these are whole new topics.
My own crank length? My inseam is 34” (86.36cm) and I now use 170mm crank arms on all my bicycles.
Back to my friend, he uses 155mm crank arms. It’s hard to argue with his choice, as he is Cat 2 California State ITT champion.
Coach Rick Schultz is an avid cyclist who trains, races and coaches in Southern California. Rick is an engineer by trade, and in addition to being a coach, he’s a bike fitter and prolific product reviewer. He’s the author of Stretching & Core Strengthening for the Cyclist in the RBR eBookstore. Check his coaching site, www.bikefitnesscoaching.com. Click to read Rick’s full bio.