Coker crank length and risk of injury link?

The basic question is: do shorter cranks on a coker increase the risk of knee injury because they put more strain on them?

I’ve recently switched from 150’s to 127’s (or 125’s, can’t remember) and felt pain in my knees after riding for a while. I’ve partially torn ligaments in both knees before so have to be careful until I’ve built my strength up. Will it be best to switch back to the 150’s and accept the lower speed, assuming you people think that they put less strain on you?

Also my seatpost is stupidly low since I cut it in the wrong place (durrr…:o)
I’ve got a new one, I’ve been recommended to put it as high as I can cope with. Should the new riding position help, since I feel a bit hunched at the moment and my legs don’t get near fully strected out on the downstroke?

Thanks for the help!

Seat height makes a real difference to my knees, I find my knees ache if I ride a long way with a too low seat…

Bear in mind that for shorter cranks, you want to raise the seatpost slightly compared to long cranks too, as the bottom of the crank circle is higher up.


Cool, thanks Joe… just what I needed to hear. Might help to explain why I have no problems on my racing bike. I just need a pipecutter to get the new post rideable now.

Anyone had any injury/pain problems switching to shorter cranks or is it just a coincidence?

Things that might hurt your knees:

  • Having your seat too low.
  • Having your seat too high (less likely)
  • Very sudden changes of load - riding a big wheel on short cranks when you have to keep changing speed and direction - e.g. riding muni, or idling.
  • Long constant loads - riding up or down long hills. (As riding down is a less natural movement it may be worse than riding up.)
  • Very long rides without changing position or resting.
  • Falling off and banging or scraping your knees - more likely on short cranks.

For steady riding with no sudden stops or changes of speed, and no long hills, you should be OK.

The key is to have your seat at the right height. Too high and your achilles tendons hurt. Too low and your knees hurt. The affectd can be dramatic and quick. I remember a ride I went on in Tokyo with Roger in 2004. We both had borrowed Cokers with the seats too low. The figured it would be ok since we were only going 5km or so. We were amazed to both get sore knees in that short distance, almost completely flat.

Given that the seat is at the right position, I find the that shorter the cranks are the LESS strain occurs on my knees and ankles. I saw it just a few weeks ago when we did a 105km ride with a very experienced unicyclist. He couldn’t find his regular cranks and ended up doing the ride with 170mm cranks. He kept up fine for the first 50km or so (amazingly cruising at 12+mph), then his legs started cramping on a big steep hill and he ended up having to sag back to the start after only 60km. This is a guy who has ridden 160km in a day and has ridden probably 20000km, over many years.

I’ve done all-day 70+km rides on 152mm cranks, but have to be careful to avoid going too fast which strains my knees and ankles. With 125mm or 110mm cranks, that length ride and longer is no problem at all. The larger the circle your legs make, the more your joints have to move. So I always use the shortest cranks possible given the terrain.


Thanks so much Mike and Nathan, that’s really useful info!
I’ll keep the shorter cranks on and raise the seat about as high as is comfortable while making sure my lower leg is still slightly bent when the cranks are vertical. I think that’s how its meant to be on a bike and judging by what you say I should be able to get it about right. Then I’ll change the cranks if it’s still giving me gip, at least that way I’ll know if it was just one factor or another. I think that makes sense, but there’s only one way to find out.
I also have a brake from a road bike that I can fit next week which should help. You’re spot on about downhills, that’s what really kills me!

yea, If you get brakes I think that wil also help a ton. I’m pretty sure brakes are very useful on the big wheels.

Longer cranks mean your knees are moving through a larger range of motion compared to shorter cranks. The larger range of motion means that your knees need to bend more and your knees are in a different position (angle) when applying the most force to the pedals.

If you have tendinitis type problems (ligaments or tendons rubbing) with your knees then the larger range of motion from longer cranks could cause problems.

On the other hand, longer cranks can mean that you put less force on the pedals when climbing or descending and that can translate to less force on the knee joint.

Twould depend on what type of knee problems you’re trying to compensate for.

Seat height is also a biggie. Riding a muni with 170mm cranks is a lot different than riding a Coker with 170mm cranks.

What Nathan said :stuck_out_tongue:

You want to use the shortest cranks possible for the terrain if you are going to be riding for hours on end. The shorter you go, the less your joints move, the less strain you get. Not only that, you are going to chafe less on the saddle.

During my 24hr Record ride I was using 100mm cranks and 110mm cranks. The 100mm cranks were much smoother, faster and gave me less saddle soreness than the 110’s.

I remember going from 125’s to 150’s when I was riding in Cambodia (which is pretty flat). I had been able to ride at least 20km without stopping. After switching to 150’s I had to stop every 5km’s cos it hurt so much. If I had to do that Unitour again I’d definitely be on 100’s or 110’s.

So for me- I use 100’s on the flat, 110’s for general riding, 125’s for hillly rides, and 150’s off-road.

100’s? thats really short…

You could go Brian MacKenzie style and ride 40mm cranks!!! I saw them…They are so tiny

are they actually usable?

Yeah…Buy TWNR…Theres a few clips of him riding his Coker with 40mm cranks in there.

Is TWNR training wheel not required? If so, where can I buy it and how much is it?

I think it depends on the nature of your injury. You just have to go with what feels best. I’m sure the advice about seat height is very important too.

I have knee ligament damage. I fully snapped two ligaments in the right knee in a skiing accident in Feb 2005. I find longer cranks put less strain on my knee, and I get more pain the day after if I ride with shorter cranks.

I put it down to the stress on the knee being applied in a limited range of movement, i.e. the knee is not being fully extended or flexed. Also depending on the seat height, that narrow range of motion might just be in the area that makes your knee worse.
While recovering from knee injury you are told that the more you can use your knee (within reason of course), the better it is for regaining full motion again. Infact unicycling was one of my rehab exercises and works well because it exercises and re-educates the muscles without impact, more so than conventional cycling or the other exercise machines they put me on. I really think it helped me a lot (my doctor agrees) and I have made an exceptional recovery.

Lack of motion is the worst thing for making the knee stiff and painful. Infact even now if I’m laid up for a day or two my knee deteriorates rapidly.

Of course I am not a doctor, I’m just telling you of my experience and what I have learnt having been through a year of rehab, it may be different for you.


Yes it is. You can get it from e-bay and im pretty sure theres a link in Brian MAcKenzies Sig that shows where to get it aswell.

crank length and q-factor

has anyone found that cokers with zero Q cranks are easier on the knees for road riding? I’ve got prowheel 127s with relatively large/high?? Q-factor right now and wanted to try 114s with zero Q.

I haven’t noticed any issues with Q-factor. When I upgraded from a stock narrow hub to a Tom Miller wide hub, I was worried that it would feel funny at least or have some other problem. But it took about 1 second to get used to it - just not a factor at all. I pretty much use Bicycle Euro cranks in 110, 125 and 152 (and occasionally 170 for very steep offroad riding). I have some Dotek 140s and Black Widow 165s that I’ve used a little, but prefer steel cranks.


Q-factor on the Coker doesn’t make a difference for me with regards to the knees. I have used a narrow hub, a wide hub with straight cranks, and a wide hub with wide (flared out) cranks. I haven’t noticed that one setup is better for my knees than another setup. But that is just an individual observation. Could be different for someone else. Some people may be more sensitive to Q-factor changes due to body geometry.

Proper cycling form and pedaling form is also important in minimizing potential knee problems. Proper pedaling form means that your knees are moving up and down in a plane and not making some kind of strange elliptical pattern when viewed straight on from the front. The knees should be moving up and down and not making any side to side movement as you pedal. The side to side movement of the knees can cause knee problems.

You can exaggerate the poor pedaling form by riding like a bow-legged cowboy. You’ll notice that the knees have to make side to side elliptical circles as you pedal (when viewed straight on from the front). That is bad form. Now move the knees in so they are in line with your hips and ankles. Now when you pedal your knees will move straight up and down in a plane (when viewed from the front). That is good form.

Q-factor can make a difference for some people for how they can pedal with good form with the knees moving straight up and down. For me, I haven’t noticed a difference with Q-factor affecting how well and how comfortably I can pedal correctly with the knees moving straight up and down. But I’m sure there are people who are more sensitive to Q-factor changes due to their body geometry (hip width, joint orientation, leg length, etc). If you notice that you have poor pedaling form you can try experimenting with Q-factor changes to see what suits you best.

This seemed like the best place to post this, but it’s not just knee pain - it’s really a general “why do people like short cranks so much?” post…

I’ve always ridden my coker on 150s, or more recently 145s. I’ve never been very good on top speed, usually averaging 12 or 13 mph and topping out at 15.

With unicon coming up I’m intending to ride in the marathon, so in the last couple of months I’ve been experimenting with 125s, just because it’s the thing to do. The first couple of rides were horrible, but I decided it was because it was on my normal commute route, which is quite rough and hilly. So I’ve done a few rides on the flat round a local reservoir. Yesterday I felt like I was a bit more used to the shorter cranks and timed myself. I did 12.5 miles in just under an hour, top speed 15.5mph. So, EXACTLY THE SAME AS WITH THE 145s! And my knees hurt afterwards.

So all the change of cranks appears to have done for me is made the unicycle harder to ride at the same speed.

I’m going to ride that same circuit on the 145s if I get time, just to prove the point, but I suspect I may even be a bit quicker due to not having to slow down for every grain of gravel on the road.

I think my speed is limited by some sort of psychological governer, not by spinning speed. I can spin faster on my muni with 150s, so that doesn’t seem to be it. I tend to average slightly higher speeds on the coker, and it’s certainly a more relaxing ride*, but my top speed in a sprint is probably almost as high on the 26" muni.

I really can’t seem to get on with short cranks. Perhaps my legs are just too used to bike cranks - using the 125s with such a small leg movement just feels really inefficient or something.

(Yes, my saddle is at the right height, 20mm higher than with the 145s)

So, will I be the only one riding the marathon on 145s?


*That’s on 145s. On 125s it’s anything but relaxing and destroys knees.