Flounce

I have seen the tables and charts online regarding appropriate crank arm length. I think mine is a 175mm, I am 6 foot 1.

I am getting over Achilles tendinitis on the one hand, while having some increasing anterior knee pain on the other hand. Bike saddle adjustments that improve Achilles stress (saddle down and forward) tend to aggravate knee pain (that , theoretically, is improved by saddle up and back).

I'm thinking that going to a SHORTER crank arm length can decrease the stress on both achilles and knee, by having a smaller range of circular motion, i.e. less knee bend at the top of the pedal stroke and, simultaneously, less achilles stretch at the bottom of the pedal stroke. I don't care about mild loss of leverage with shorter crank arm, I don't hammer/mash when I ride, I spin seated.

If I experiment with shorter crank arm, I will need the bike fit re-done, which is not a small thing and needs the blessing of my fitter if he is going to re-fit me.

My bike fitter, who is very good and has experience fitting RAAM riders and such, says "no" - crank arm length doesn't have a role in decreasing my anterior knee pain without aggravating my now-improved achilles. My logic says otherwise, but what do I know compared to him.

I am asking this forum because I want your real-life experiences with crank arm length as ultra long distance riders. When I want a theoretical answer/musing based on logic, I'll go ask the bike fitters forum

Thanks!

noglider 

If you have a repetitive stress injury in the ankle, perhaps your saddle is too high.

But don't listen to me. You really should get professional advice.

Crank lengths matter to some people and not to others. Some are really sensitive. If you secretly swapped my cranks to shorter ones, I would not notice, but I'm almost sure to notice if they are longer than 170mm. I even have a bike with 155mm cranks, and they don't feel different at all.

OneIsAllYouNeed

My experience with Achilles pain during long distance riding is that it is aggravated by high force/low cadence riding. [Relatively] shorter crank arms should encourage you to spin [relatively] faster. Otherwise, Achilles pain for me has been independent of crank arm length, cleat position, and saddle position.

Anterior knee pain can also be instigated by cumulative mashing.

I'd recommend recording your cadence during long rides. It may be lower than you think. Try increasing it by 5-10 cycles per minute.

I've successfully followed some recommendation from this site (no affiliation) for pain diagnostics and self-fitting purposes: CYCLING PERFORMANCE TIPS -
By the time I finally got a professional fit done, nothing moved by more than a few millimeters.

Carbonfiberboy 

I do weight work at the gym for all that sort of thing, very gradually working up to as much weight as one can do 5 reps with. Depending on the location of the anterior knee pain, it might be possible to strengthen a particular quad muscle to fix it. Long distance cycling give one RSI and the only way I've found to diminish the tear-down is by building up. For me, crank arm length doesn't seem to matter. I'm 5-6" and ride 170 and 175 cranks without noticing the difference, which is teeny anyway.

Chris Pringle

I personally changed from 175mm to 170mm cranks after my first 400 Km brevet and experiencing a bothersome knee pain (no issues on shorter brevets with 175mm cranks). I noticed it made a huge difference on the 600 Km brevet with 170mm cranks. You might to adjust your saddle height if you do this. Somehow my saddle height had slipped down for PBP (most likely as a result of taking the bike apart for travel) so I was having some knee pain just after 400 Km. I raised my saddle a bit and my knee pain got better -- almost as if my knees magically recoverd while riding. I started experiencing knee pain again but it was around 1,100 Km which I figured it was normal given the distance. Took some anti-inflammatories after the big ride and rubbed some bengay-like gels and I was fine the next day.

Given the stress one puts on knees during brevets (and the training for them), it is of utmost importance IMHO to take glucosamine-chondroitin as supplement for your knees or you risk having arthritic-like pains or symptoms. If the goal is to accomplish the S.R. Series in one season, it is too much stress on the knee joints to quickly recover before getting back on the bike again for more training and another long(er) brevet.

Since there are no bike fitters where I live, I have learned over the years to listen to my body, educate myself online and then make appropriate changes. It has worked really well for me. Generally speaking, pain is no good even though there is a certain level of body discomfort associated with randonneuring. It is important to understand the difference as pain can lead to ugly long term conditions.

Chris_W

I made a post on the Ride Far blog a couple of weeks ago about Crank length and comfort for long-distance cyclists. My intention was to encourage people to think outside of the overly-narrow 170-175 mm box that bike and component brands are happy to force us into.

Since posting the article, nearly all of the feedback that I've received from ultra-distance riders has been about how using shorter cranks than recommended has alleviated a variety of joint problems (knee and ankle). Not pushing your ligaments/tendons to their limit on every revolution and encouraging a higher cadence seem to be major advantages for many people.

I'm not a big fan of listening too closely to what a professional fitter has to say; I far prefer just trying different setups and seeing how my body responds.

Rowan

I moved from 175 to 170 cranks when I built up my fixed gear back in 2007. The base bike, including cup and cone BB and cranks, was a dump find, and the cranks happened to be 170mm.

I did some thinking about the rotational distance a person pedals on a big ride. I did some thinking... not some calculations... but the premise seemed sound.

So the 170s stuck. Notably, since then, I haven't had any significant issues with knee pain, but for saddle height and cleat adjustments.

I don't think any of my bikes have 175 cranks anymore. However, one slight change did occur. I like remaining seated with right toe on the ground when starting from a stationary start. A shoter crank length meant a slightly higher seat height and now I need to be "tippy toe".

I am not inclined to change what works for me at the moment, so 170 will remain my gold standard for a while yet.

Flounce

Thank you, all, for the advice.

I'm going to work some more on knee strengthening and ITB stretching and see if the knee pain improves. If not, I'll switch to 170mm.

unterhausen

I used to think that 172.5mm were too long for me, but now that I do a lot of mtb'ing and gravel riding on 175's, I can't really tell the difference between my bikes. On my road bikes, I use a 170mm crank. The big difference for me is q factor, but that goes away quickly after I start the ride. I do think that it is really easy to let yourself slip into a very low cadence on longer rides. I see that a lot on 1200k's. My friends often make fun of me for spinning at slow speeds, but on the last day of a 1200k I'm still at the same rpm and everyone else is grinding away in a big gear.

rhm

What tables and charts are you referring to? I ask because I've looked at all such charts I could find, and in the end the only thing I learned is that Zinn thinks longer cranks are advantageous, Burrows favors shorter ones, and hardly any other theorist pays any attention to this at all from a performance point of view.
There is a commonly held view that shorter crank arms are easier on the knees. Not suffering from knee problems myself, I cannot comment on that.

I'm 6' tall and began experimenting with shorter crank arms about ten years ago. I only rode 140's for a few years, then 150's and 152's (6"). The only problem with cranks that short is that they are poorly made. Decent quality cranks shorter than 165mm are very rare. So I eventually settled on 165 as my preferred size.

My takeaway is that shorter cranks have no performance disadvantage when riding on roads. Longer cranks offer a little extra leverage that can help you get over obstacles like fallen trees, but even better is to avoid the fallen trees entirely. The only disadvantage I can mention, regarding short crank arms, is that once you get used to then (which takes less than an hour), switching to longer ones is no fun.

I guess we've all noticed that our preferred cadence drops over the course of a long brevet. That has certainly been my experience, anyway. But i don't see how that's really relevant to this discussion.

unterhausen

I think it's natural to assume that longer cranks go with lower cadence. But really, higher cadence is a matter of practicing riding at higher cadence. I can spin the 175mm cranks on my gravel bike just fine. My spin usually gets a little wobbly at around 110rpm. When I'm going for the win at the Wednesday night world championships, I am sure I have gotten to higher cadences than that. I just have to concentrate on smoothing things out a little.