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 product reviews website, www.biketestreviews.com, and his coaching site, www.bikefitnesscoaching.com. Click to read Rick’s full bio.
Sandy Sutherland says
Is it possible for you to make some general comments about disproportionately long femurs vis a vis crank arm length?
Is there a relationship?
Would disproportionately long femurs infer longer crank arms at least be worthy of consideration?
Perhaps there would be an inherent advantage?
I realize the breadth of inputs you use, and how picking out just one element is not a good way to decide upon a specific length, but my guess is that there is some kind of relationship between the two.
John Sinibaldi says
There is a lot of information, misinformation, outright ridiculous claims, etc. about crank length. I’ll give you my take on it: I’m 6’6” tall, have a 35 inch inseam, and ride 190mm cranks and while I’m getting older and slower, I was pretty fast and strong in the day.
Why do I ride 190 cranks? Twenty-five years ago, I was riding 175 cranks and having knee issues. The prevailing thought back then, if everything else on the bike fit was correct, was to go to shorter cranks. I did, and my knee problems got worse.
I stumbled across information on crank length from a gentleman named Kirby Palm (his website is no longer up, but Google searches will return links to his information). In a nutshell, the one thing I took away from his analysis was this:
If the optimum knee and hip angles for, say, Peter Sagan is X and Y (which maximizes power output and comfort while minimizing injury), then why wouldn’t those angles be the same for me?
Once I bought into that idea, I realized that my optimum crank length would be quite a bit longer. I wound up going with 190mm, which was a bit shorter than the recommended length from both Kirby Palm and Lennard Zinn (from whom I buy my cranks), but within a week of installing the cranks, voila! No more knee pain.
And addressing the elephant in the room (cadence), I have no problem maintaining a cadence between 88-92 for long stretches, although with the longer cranks, I can also “loaf” along at a much lower cadence and bigger gear when riding in flat or rolling terrain and conserve energy. Having those longer “levers” makes whatever kind of riding I do much more flexible, while aiding me both in climbing and sprinting.
I’ve been pain free ever since, ride some 250-300 miles a week at 67 years old, have done a bit of racing on them with good success, and will NEVER go back to cranks that are too short.
Lennard Zinn makes custom cranks in lengths from the very short to the very long; for those of us with long legs, going with a longer crank may be the very thing to take cycling to the next level.
One caveat: With 190 cranks on a standard frame (in my case, 63cm when I was buying “off the rack”), the typical bottom bracket drop means that if you’re not careful, you’ll drag the cranks in corners (or worse, hammer through a corner and hop the bike off the ground which could cause an accident). Unless you’re really riding hard with a lot of cornering, it’s not a problem – but in my case, I wound up going with custom frames over the past 20 years, and by doing so could spec a bottom bracket drop that is 1 cm higher than the typical drop for a frame my size. (My custom frames measure in at about 64cm, with a long top tube to accommodate my long arms).
Just one tall man’s thoughts on crank length, and by all means, this is not advice for anyone. 🙂
Kerry Irons says
When I first got into cycling in the late ’60s, every racing bike came with 170 mm cranks and TA was about the only widely available source for other lengths. The “best” length has gone up and down over the years and now we’re back to 170. I wonder why that is 🙂
The “logic” of “crank length should be proportional to leg measurements” has been around for a LONG time, and lots of people have turned that “logic” into a formula for determining crank length. Only one problem: the research doesn’t support it. One key feature that is often ignored in these discussions is the duration of muscle contraction that is controlled by cadence. It just may be that there is an optimum here, which is why there is a fairly narrow range of cadence for optimum performance. Longer cranks tend to mean lower cadence, moving you out of that optimum range. Crank length has been a point of debate since the introduction of the “safety” bicycle in the late 1800s, and there have been all sorts of fads in that regard.
A 2008 study by Jim Martin, Ph.D., from the University of Utah shows zero correlation between crank length and any performance factors.
Fred Matheny Summary: There have been studies of crankarm length, but the results aren’t consistent. Some show that longer cranks provide greater leverage for turning big gears. Some show that shorter cranks foster greater speed via a faster cadence. And some show that crank length is completely individual.
While Kriby Palm was quite the zealot for crank length formulas, he we never able to provide anything beyond his opinion to support his claims.
Russ Marx says
Ten years ago there was a movement to shorter crank arms & higher cadence, “more rpm equals more power”.
Haven’t seen anything about it since.
Jim Langley says
Rick wrote: “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.”
Just to explain in case any readers wonder, ITT stands for Individual Time Trial. In time trials one rides in an pretty extreme aero position.
In this extreme aero position if you use standard crankarm lengths, your knees will come up each pedal revolution and may hit you in the chest – and even if they don’t hit your chest, it’s an awkward pedal stroke over the top each time. That’s why lots of time trialists choose shorter crankarms.
Personally, I have a 32 inch inseam and on my time trial bike I tested crankarm lengths of 172.5, 170, 165, 160 and 155. I found that the 160s were the best for me and like Rick’s friend I won the state ITT championship on them. But I ride 170mm cranks on my road bikes.
John Sinibaldi says
Jim Langley, just to muddy the waters a bit, Miguel Indurain, arguably the best ITT rider of his era, used 180 cranks for almost all of his time trials and for the Olympic gold in the ITT in 1996, and 190 cranks for his hour record (the ultimate ITT, imho), riding at an average speed of 53.040 kph (32.9+ mph). Ondrej Sosenka set the record Merckx-style in 2005, also riding 190 cranks, at an average speed of 49.7 kph (30.8 mph).
Clearly some people can still put incredible power down with longer cranks while holding incredibly aero positions on the bike. Just saying. (And I’ll bow out of this discussion at this point, because optimum crank length will ultimately be determined by the rider and their performance).