Increased leg stress and short cranks?

I have ridden 165-170mm cranks on 26-29" wheels for the past three years, averaging three to four rides per week, typical ride time 1-2 hours during the week, 3-4 hours on the weekend rides, max distance ~20 miles, riding 90% single track/ 10% double track, no road riding. In general, other than sore shoulder, quads, and taint, I have been pain free. I do warm up before rides and stretch when I take breaks from riding.

This past summer I decided to gradually decrease the crank length on my primary muni, KH 29, to improve efficiency. First I went down to a 160’s and rode those without much problem, though I did notice I needed to use more brake on downhills and I was out of the seat more for both up and downhills.

About one month ago my left knee started to get “twingy” at the end of long rides. This feeling did go away between rides and wasn’t a problem during shorter rides, though at times I did notice some shin pain when walking/hiking. Fast forward another week and I was riding a twenty mile race, when I started having significnat knee pain ~ten miles into the event and it persisted until the end, even after taking ibuprophen.

Intending to further improve pedaling efficiency and thinking that a shorter crank might reduce knee stress, I reduced my crank length to 150’s on the 29er. In the meanwhile I let my legs rest for a few days, then gradually increased my mileage to pre-race levels. I didn’t notice any knee pain until this past weekend when I rode ~ ten miles (three hours) of tough single track.

I have a fair amount of experience with endurance sports and have dealt with chronic use related injuries such at piriformis syndrome, compartment syndrome, shin splint, ITB issues, etc…but this problem seems to be completely isolated to my left knee, only bothers me during long ride, and seems to be at it’s worse on downhills when my knee is unable to straighten; yes, on uphills where my leg is more extended, my knee feels fine.

I have already done ICE, stretching, NSAIDs, etc…so my conundrum is whether by running a shorter crank am I overstressing my knee as a result of having to work harder to control the uni?

Note: I don’t want to hear about stretching, physical therapies, meds, or anything that I can do to treat the “injury”. I’m asking about experiences and theories relating to
crank length and leg stress.

Another factor to consider is saddle height/position. From what I’ve read about cycling and incorrect saddle height/position is knee related issues like you describe. I know for MUni that we all tend to ride with the saddle a bit lower than we would for road riding. The assumption is that for road riding we have the saddle height/position dialed in perfectly to avoid knee issues i.e. avoiding either extreme of full leg extension when cranks are at the 6 o’clock position or legs too bent. However, for MUni we’re riding with the saddle much lower thus it seems to me we run the risk of having knee related issues, particularly if your riding in the saddle for a prolonged amount of time. Now if your on and off quite a bit I’d expect any issues would not be as pronounced.

I’m going to experiment with riding MUni with more of a “road” saddle adjustment when I come back. Perhaps a bit lower saddle than I have now but nowhere near as low as I had it. When I started exclusively riding roads I ended up adjusted the saddle height up over 1/2" for the same crank size.

As for leg stress with respect to crank size I have no opinion on that, other than feeling faster all around with a bit shorter crank than I was used to riding in years past I can’t say I feel any more/less fatigued or pained (outside of my current leg issue which I strongly believe doesn’t correlate to changing from 150mm -> 137mm crank sizes, I think I’d have my issue regardless).

Just my two cents…

I did some on-line searching for crank length discussions, most of which was in road niking forums, none of which seems to be very “scientific” and all were factoring in gear changing ability. In terms of sizing, the standard seems to be adjusting crank length for rider inseam, so taller riders get longer cranks, etc…

There was a good discussion on an recumbant forum about knee angle and how applying pedal pressure at anything less than 90 degrees of opening will cause increased stress and injury because you are essentially “forcing the knee apart”.

In all of this discussion I did not find anything that directly applies to unis as we are not only single speed, but fixed, so we have additional resistance forces to consider, as well as (for muni) needing to out of the saddle to accomodate uneven terrain since we lack suspension and the ability to coast.

I believe a longer crank allows more control over speed on the downhills, which seems to be supported by my increased need to brake, as a result I believe my legs are working harder on downhills (poosibly uphills) to control the uni.

This is true. The general rule is that your seat is going to be lower for any type of rough terrain riding. While an “optimum” seat height works for road riding (unless it’s real bumpy), we don’t have a choice but to go lower for the rough stuff. Otherwise you eventually end up getting bounced off the seat, losing pedal contact and doing some unintentional coasting. So yes, the lower seat is a necessity. I will often make seat height adjustments on rides that contain long climbs (higher) or long areas of challenging terrain (lower).

Very little of that information is relevant for us with one speed and one wheel. When you can choose your pedaling speed, it changes the equation.

That sounds very relevant to us, at least as a general rule. If your position results in a 90-degree or less angle of knee, it’s probably not good for your knees. I will also point out that the recumbent part of that equation plays a role. On a conventional bike, your pedaling force comes from leg power with the addition of gravity. When out of the saddle, you can add a little more force by pulling on the handlebars but that’s about it. On a recumbent you have that seat back there, which allows you to put more power into the pedals and can add to potential knee strain. Still, 90-degrees sounds like a good general rule of thumb until some unicycle scientists come up with something better.

Sounds obvious enough; I have no reason to doubt this. Beyond adding a brake, unicyclists don’t have much in terms of options. You can’t ride Downieville with a high seat, for example. That’s 4000’ vertical, much of it on technical terrain. Naturally it will help to increase your braking skills (a weak area for me as I have no MUnis with brakes). This will allow you to take on more difficult downhills without having to wrestle the pedals as much. The other thing you can do, which seems to work for me in places like Downieville, is to ride faster. That may sound stupid, but I think it makes sense. You’re spending less time per rotation resisting those back pedals, and less total time doing the whole process. Combining this with good fitness to handle the ride at hand, and it seems to reduce the strain on the knees.

I would say that you definitely have more stress on your legs with shorter cranks, especially if trying to keep your speed in check without using a brake.

I know you don’t want to talk about your “injury” but it sounds an awful lot like what happened to my knees when I was training for RTL. I was developing some pretty bad muscle imbalances and it was pulling my kneecap out of alignment once the stabilizing muscles would get sufficiently fatigued.

I don’t know if my story would interest you, but I’ll go ahead and tell you anyway.

I sprained my ankle 2 months ago while learning to ride, but have since recovered from that.
However, a month ago I changed the 150mm cranks on my 25" to 125mm ones. I’ve been riding mtb and road regularly since last year, and I must say that the back pressure on the 125mm cranks was initially shocking (compared to 150mm).

I just discovered I’ve developed Achilles Tendonitis on the right ankle and started a thread. I’m not sure what exactly caused it, but I suspect it must be some residual damage from the sprain, combined with short cranks, and my beginner rider status (lots of wasted energy and corrections). I’m going to stop riding for a month.

The pain in your knee sounds familiar, I started to have the same problem in my left knee when I was in the army. Now I avoid all impact sports like tennis, badminton, basically anything with running. I sometimes get a slight ‘twingy’ feeling if I’m on my mtb for too long.

In the 2 wheel world, a great deal is made about KNOPS (knee over pedal spindle). But this is hard to achieve with unicycles.

After sustaining a knee injury brought about from a stent of excessive training on my single speed mtnbike I, on the advice of my doctor, had a “Bike-Fit” performed. The results revealed that my seat was too far forward creating stess on my knees during the power portion of my pedal stroke. I installed a new seat post and have not had a problem since.

Due to the whole balance thing we unfortunately cannot adjust our seats back in relation to the cranks, however it would seem to me that shortening the cranks places the knees farther forward over the pedals creating the same problem as my seat position on my mtnbike.

Only my experience and observation for what ever it is worth.

It might be worth reading up on meniscus tears, you might have a minor one. I (re)tore mine last January. In the beginning I could barely walk, after about two months I had healed to the point where I had symptoms similar to what you describe, but while walking. Walking uphill didn’t hurt at all, I experienced sharp pains when walking downhill. For me the pain was located on top, almost as if it were above the knee, centered and felt like it was an inch or so down.

My first bout with this injury was when I was a kid, I had a severe tear and couldn’t bend my knee at all for about a week. The re-tear this past January occurred about 25 years after that initial tear. It happened when I fell asleep on the sofa with my leg sideways and my knee bent - forming a triangle. The cat thought the nook my leg formed was the perfect napping location. The sideways pressure against my knee with my knee bent did it, I woke up a few hours later and that’s all she wrote.

Anyway, that re-injury healed slowly 1-2 months of sharp pain just about all the time, 3-4 months of the downhill walking pain, and only went away to the point where I was no longer bothered by it after 6 months. I can still feel a twinge now and then. It’s a slow healer since there’s not much blood flow to that area.

You’re usually pretty safe from this sort of thing while cycling, as I understand it usually occurs when lateral force is applied to one of the sides of a bent knee. Usually there are no external forces pressing on the side of the knee when pedaling, but I could see a fall or some hardcore muni-ing creating a bit of a strain.

So if this only happens with shorter cranks but goes away with longer ones the meniscus probably isn’t your problem. If it were then after than initial pain you’d likely continue to experience the pain on the longer cranks. Sorry for the epic time waste.

No knee injuries ever, no high impact sports, no inflammation to speak of, no unusual clicking or hanging up. The knee doesn’t bother me except toward the end of a long ride. The shin pain may be unrelated since I have suffered from shin splints since I was a teen.

Of course there is always a possibility of muscle imbalance, but I’m pretty fit and I cross train, always allowing for recovery, know when to sit out and rest, and this is a new problem since going to short cranks; ie my knees have never been a problem as long as I can remember and I have been an avid rider/runner/skiier for 30+ years.

I suppose I answered my own question, though I am curious if anyone has gone to short cranks, then went back to long for similar reasons.

The real “sucky” part of this is that I actually enjoy riding my 29er with shorter cranks, so I’m reluctant to go back, but at the same time if that’s the problem I really have no choice because it has limited how far I can ride :frowning:

Note: Raising the seat did help “a little”, but I can only raise the seat so much before I start getting “kicked off” on rough terrain.

Yes, I think there is a relationship between crank length and leg stress. But I think the difference comes mostly from the leverage change, being a function of the ratio of crank length to wheel size.

I was attempting to train for long distance riding early this year. I started out on my Coker with 152mm cranks. Then I bought a Schlumpf hub and put it in my KH29, with 150mm cranks. Just a few days of riding around the neighborhood in high gear resulted in pain in my left achilles tendon area. This was a re-injury, and exacerbation, from over doing it while road recumbent riding a few years ago. I ended up in a couple months of physical therapy, didn’t ride hard this summer, and it still bothers me a bit 6 months later. Official diagnosis was calf strain, but I think I have some tendonitis as well.

Prior to swtiching to the Schlumpf, I’d never had any discomfort in my achilles from unicycling. Prior crank lengths had been 150, 125, and 165 on the 29er (in order of amount used), and mostly 152 but a little 125 on my 36er.

From my experience, it appears to me to be the amount of leverage, taking into account both crank length and wheel size, that dictates leg stress. (Although length alone could also be a factor, particularly for riders with longer legs.) I think your switch to shorter cranks probably increased the strain on your legs in a manner similar to how adding the high gear did for me.

Edit/additional thought: Shorter cranks don’t really make a significant difference in speed. The only way to significantly affect speed on a unicycle is to change the wheel size or add a geared hub. So best bet is to just ride the cranks that are most comfortable for your body. This helps avoid injury, and keeps it fun. To the extent crank length does affect speed, I think comfort is just as much a factor, so that higher comfort on longer cranks probably cancels out any speed advantage of shorter cranks anyhow.

Running is definitely a high impact sport. Unicycling can be high impact, as muni UPDs on rough terrain will add up for longer rides. I have hip problems and get referred pain to the knees sometimes, but have never experienced problems relating to short cranks. Its always the impact of UPDs that make my hips unhappy.

I started at 150mm on my kh29 and moved to 125mm after a few months. I’m generally happy at 125, but could use more crank to maintain control on steeper descents. I plan to try 137mm moments and see if they are a better fit for me.

I’m also trying to standardize on 125mm for both 36" and 29" (mainly road), and when I used to get tweaked knees, I’m convinced it was because the Venture cranks had zero q-factor. When I bit the bullet and bought KH cranks because of the wider q, the tweaking in my knees went away. For me, I need to have my legs wider apart when I ride.

my own exeriences:

  • On Coker switched from 150 to 125 then back to 140
  • on 24" Muni with brakes from 170 to 140
  • on 29" (without brakes) from 125 to 110 then back to 150
    to avoid knee pain it appears that my comfort zone is around 140/150 (150 on 29" being for control when going down).
    So yes: for me crank length has some effect on knee pain.
    I spin very slowly but decided on a trade-off: better keep my knees and go slowly. I am wondering if a geared uni is an option suited for me …

Haven’t been riding too long and use 137/165 moments on my 26". I have found that my knees tend to have more problems when on 165 than on 137. I am quite tall and suspect that the problem lies with the amount of knee bend on the longer setting. There is more control on longer setting, but the comfort on my knees and legs is much better on 137. Another thing that I noticed makes a big difference is that I have to adjust my seat higher when on the shorter crank length, there is a relationship there.

I know that this sounds contrary to your experience Ben, but for me it just goes to show how individual these kind of things are. It’s really difficult to find a “rule of thumb”.

Well I bumped back to long cranks, downhills area easier and less stressful, but my knee remains sore and now my right knee is feeling tweaky. So I sat down to ponder the problem and I may have figured out the change that led to my knee pain: Lower Q factor.

When I went from 170 to 165-160, then 150, I went from a high Q to a low/zero Q. The difference in width from the QuAX 170 to Venture II 150 is a solid inch, a half inch per side, which would force my feet inboard and change the pressure on my knees.

I had noticed how my feet wanted to be on the outside edge of the pedal and now I know why: it’s too dang narrow!

So, back to Moments, gonna stick with 150’s, long term I’m looking at transitioning to a 125mm disc hub and low Q cranks.

Wide is in :slight_smile:

I had knee pain many years ago when riding Muni- it seemed to be worse on descents with long cranks. From memory I was riding 170mm/24".

I ignored the problem and it went away, but I didn’t feel that pain on my shorter cranked Road Unis. It probably has more to do with the greater range of motion your joint goes through than the actual amount of pressure you put on the joint. After all, unicycles are very lowly geared machines.

The strange thing is that I don’t get it when riding bikes, which have much longer cranks. So there must be something mechanically different as well- perhaps I angled my leg out a certain way (it only affected my left knee) when descending on a Muni (I didn’t use brakes), or the way you have to exert back pressure on the pedals when going downhill.

Length v. “Q”


Interesting topic. As a 50-something year-old rider, maybe I can add a slightly different perspective to the discussion.

I remember when I got my Nightrider 36er a couple of years ago. It came equipped with the original Nimbus Venture cranks in 150mm. They seemed to have almost no Q-factor compared to the 165/137mm dual hole KH Moments that I had on my N24 MUni at the time. After the first few tentative rides on “the beast” my knee pain was so intense that I thought I may never be able to ride it more than about 5 miles. I also remember the stabbing pain in my knees when going down stairs the day after riding the Nightrider. It was so intense that I seriously almost gave up on riding 36ers altogether.

Then, one day, after deciding I was going to try to commute (6.5 miles, one-way) to work on the beast, I decided to swap the 150mm Ventures for the Moments on my MUni. My main motivation for making the swap was that I needed more torque to climb some of the hills on the way to work and back. (My other motivation was to try the 150mms on my MUni after discovering that I didn’t like the 137mm setting.) The unexpected advantage after that first commute was that my knee pain, while still present, greatly diminished with the Moments.

The problem, of course, is that I changed both variables at the same time, so I can’t say which one (length or “Q”) resulted in reduced knee pain.

One thing I can say is that the extra 15mm of the 165mm setting (and possibly the increased Q-factor of the Moments) made a huge difference in my ability to control the big wheel. This allowed me to be more confident, and less herky-jerky on the pedals. I think that the added control, especially when descending hills, and the increased torque of the longer cranks, combined to give my knees a bit of a break, and resulted in less stress, and hence, less pain. Eventually I was able to build up enough strength that knee pain, while still present occasionally after long rides (i.e., 20 miles), is no longer the debilitating issue it once was.

But there’s one more test yet for me to do… a couple months ago I moved the dual hole 165/137mm KH Moments that were on my Nightrider to my new fixed wheelset for KH29, and I replaced the Moments on the Nightrider with 165mm Nimbus Venture II’s. I have yet to take the Nightrider out for a long ride (because I’ve been having too much fun on the 29er on trails). However, if the knee pain comes back with a vengeance after a longer spin on the 36er, I’ll be right there with you in blaming it on the near-zero Q of the Venture II’s. If not, I’ll conclude that either 165mm = 165mm, or that I’ve gotten stronger (which is most definitely the case) and my knees can take the abuse better.

Stay tuned…


I definitely find it’s the force/pressure on my knees that make them hurt, not big range of movement. Riding my 36er on 125s makes my knees hurt (it’s quite hilly here), but 145s are fine as long as I’m careful (although I did have problems with my knee while riding the 36 home from work a few months ago - took a few weeks to get back to normal).

I never have a problem on the 29er with 140s or 26er with 150s. Or on bikes with 170s for that matter. I’ve always been a spinner rather than a slogger on bikes.

Some people report knee problems on long cranks, and claim it’s down to the extra range of movement. I’m definitely of the opposite opinion - extremely short cranks (by which I mean 125s and below on a 36er) are not good for my knees (and generally horrible to ride IMO, but that’s a different discussion entirely). Must be different problems, as there seem to be a number of people in each camp.


Long cranks bother by knees

FWIW I seem to be in the opposite camp. I used to ride on the road with my KH29 and 125mm cranks and I found that my knees were happy on a hilly course (and I didn’t use brakes) but gave me grief on a flat rails-to-trails course where I was spinning faster. On the other hand, my knees don’t have a problem with riding the flat course on a 36er using 125 cranks, presumably because of the slower spin rate. I’ve also found working hard on flexibility has been a big help. Lately I’ve been doing mainly muni with 150 cranks (without brakes) and my knees are happy with the slower spin rate.

Last night I swapped out the Venture II 165’s (low Q) for some Moment 165’s (high Q) and went for a trail ride.

Knees twinged for maybe thirty seconds and never bothered me again.

In contrast, I rode trails on Sunday with the Ventures and my knees bothered me the entire ride.

The difference in Q is ~ 2.5 cm as measure from outside pedal insert to outside pedal insert.

I had started playing with crank length at about the same time as I went to low Q cranks (Ventures and K1).

So, since I like 150’s on my 29er best, I’m going to get some Moments 150mm and see how that feels :slight_smile:

BTW, the new Nimbus disc hubs have 125mm spacing (100mm is standard for non disc unis), so a low Q cranks used on those hubs would equate to using Moments on a standard hub. I’m probably moving toward that new hub standard to get disc brakes on all my unis, had previously worried that a wider hub woudl be a problem, but apparently it’s a solution for me :slight_smile:

I’m a bigger guy (200#/6’), big boned, wide hips (36" waist), so I’m thinking that the wider stance must be more relaxing and less stressful for my body type. From my teens I did lots of long distance bike touring, some race training, and I never had a knee problem. Standard crank width is ~125mm on contemporary mountain bikes.