Those with shortened cranks

[Joe.B]

This is quite topical for me as I’ve just returned from a 5 day tour of Skye, Uist & Barra with my knees and ankles in pieces. It was spinning the bent fully loaded with winter camping up the hills on skye that did it for them. The pain didn’t stop me riding but walking was quite painful.

I’m not short at 6ft and I’m already running 165mm cranks but maybe I should be trying 155’s.

I’m not going to rush out for shorter cranks just yet but I shall look at how longer rides affect my knees and ankles as the year go on and make a decision later.

[landsurfer]

Landsurfer... there's some biomechanics to deal with in here. Lift a kilo next to your body, then do the same work a metre out...

Think i mentioned moment arms in my post. ???

[[XAP]Bob]

It's not just moment over gear ratio though. It's to do with the muscles efficient/effective ranges of contracting

It's far more complex than physics...

[landsurfer]

This is quite topical for me as I’ve just returned from a 5 day tour of Skye, Uist & Barra with my knees and ankles in pieces. It was spinning the bent fully loaded with winter camping up the hills on skye that did it for them. The pain didn’t stop me riding but walking was quite painful.

I’m not short at 6ft and I’m already running 165mm cranks but maybe I should be trying 155’s.

I’m not going to rush out for shorter cranks just yet but I shall look at how longer rides affect my knees and ankles as the year go on and make a decision later.

Suspect you answered most of your problems and issues in your post .......?
How will shorter cranks reduce the force required to move your "bent" up a hill fully loaded with winter camping ?
Your cadence will rise, but surely more repetitions per mtr will make the knee/ankle issues worse ?
I think we need some clever maths here ..... any clever maths out there ?????

[[XAP]Bob]

Depends if the issue is reps or load...

[landsurfer]

It's not just moment over gear ratio though. It's to do with the muscles efficient/effective ranges of contracting

It's far more complex than physics...

Must disagree, it IS physics ... and bio-mechanics, as was pointed out by a previous poster .... An objective approach would be good rather than a subjective one .... there must be some Science on this folks ?
I am genuinely interested in the Mechanics of this post.

Personally, i ride 175 cranks with a single front ring (38 tooth) and an 8 speed block (12 -32).... since dispensing with the upper and lower sprockets on my triple setup all my knee pain has gone ...... but why ?????

[[XAP]Bob]

I meant that the biomechanics was much more complex than the simple physics.

There is basically no chance that the contraction of muscles follows any simple relationship and every chance that that relationship varies according to speed, work done in the last hour, work done in the last ten seconds as well as what the owner had for tea.

Once a force is generated at the pedal then it's all easy physics - but before then, it's a messy subject.

[hercule]

I've no great insights other than my own experience. On the biological side of the interface, a variety of factors will be relevant, I'm sure - joint flexibility - ankles, knees, hips; muscular strength; type of muscle fibres predominating (fast vs slow twitch); circulation. I suspect that means there is no simple answer, what works for me won't necessarily work for anyone else.

I bought a 152mm triple second hand a number of years ago (the same model as ICE offer). It sat and gathered dust, I was sure that the the tiny big ring (44T) and the consequent loss in gear inches would just have me twiddling along slowly. Then on a whim I decided to fit it to my Fuego. I wondered if it would help with my knee discomfort after moderate rides, and hoped another benefit might be less heel strike (an effect of big feet and relatively shorter legs!).

I've been pleasantly surprised by the results. Less knee pain, less heel strike, and I spin much faster - on 170mm cranks I typically average 90 rpm, on the shorter ones it's just under 110 rpm. I seem to go just as quickly (or slowly!). Hills are less of a problem paradoxically, I think because I spin up them more than I could before and there's less of a wobble at slow speeds as a result. It felt a bit weird at first - like trying to run with tiny steps - but after a couple of miles I stopped noticing it. According to Sheldon Browns's concept of "gain ratios", 44/11 with 152 cranks as 48/11 with 170 cranks on a 26" wheel, I feel I'm just slightly undergeared but not by much.

Relevant biomechanical factors might include the fact that I'm not very flexible, and the fact I do a lot of running (with a less knee flexion on average than turning 170 mm cranks requires, I suspect).

The knee problem has never affected me riding uprights, and I don't feel any urge to try short cranks on them. There does seem to be biomechanical differences riding recumbent vs upright - for example on the bent I do much better with cleats positioned much further back in the shoe, to the extent that I have different shoes set up for upright and recumbent riding.

YMMV, of course!

[landsurfer]

I have absolutely no experience of recumbents ...
So..
Is it possible the position is not optimised for the human skeletal form ?
If you ride on a traditional upright (traditional because it works for the vast majority of humans) do you suffer from the same trauma ?
As an Engineer i have viewed riders of recumbents, during various sportives, and all seems well until hills appear .....
Just as there is an optimum crank length (?) there must be an optimum riding position ??????
The ultra long distance rides on recumbents means that they have mechanical efficiency ... but riding a relatively flat route for 12 months is an amazing achievement but not a stake in the ground for the cycle type ......
Please feel free to put me right ....

[[XAP]Bob]

I have absolutely no experience of recumbents ...
So..
Is it possible the position is not optimised for the human skeletal form ?
If you ride on a traditional upright (traditional because it works for the vast majority of humans) do you suffer from the same trauma ?
As an Engineer i have viewed riders of recumbents, during various sportives, and all seems well until hills appear .....
Just as there is an optimum crank length (?) there must be an optimum riding position ??????
The ultra long distance rides on recumbents means that they have mechanical efficiency ... but riding a relatively flat route for 12 months is an amazing achievement but not a stake in the ground for the cycle type ......
Please feel free to put me right ....

On the basis that the early adopters were not top flight racers and dominated road races as well as velodromes in their day - I think you're wrong.

The hunched over 'form' when riding a rover safety bicycle is hardly the result of biomechanics research.
The mechanical efficiency is better, even uphill (see Dave McCraw's work with a power meter), although it appears that the max power input is lower.

I'm not saying that 'bent is optimum because there are *so* many things you can optimise for, and so many different 'bent positions. Similarly there are many 'upright' positions...

[landsurfer]

Not sure how I can be "Wrong" .....
I asked only questions, and hoped for considered response.

[Dave W]

I don't fully understand the reason recumbents give more knee pain apart from the extra weight of them. Surely the distance to the bottom bracket is identical to a diamond frame? Is it something to do with KOPS? I've not checked mine.

[[XAP]Bob]

Not sure how I can be "Wrong" .....
I asked only questions, and hoped for considered response.

Only that you said 'put me right'

[hercule]

I don't fully understand the reason recumbents give more knee pain apart from the extra weight of them. Surely the distance to the bottom bracket is identical to a diamond frame? Is it something to do with KOPS? I've not checked mine.

You can exert substantially more force on the power stroke by pushing against the seat, possibly even unconsciously - if you do that on a DF, you just rise up out of the saddle. I suspect that is my problem on the Fuego and that the rapid cadence and shorter power phase reduces the knee loading. I don't get it so much on my Trice, which has a mesh seat (more complaint?), compared with the rigid GRP seat on the Fuego

[531colin]

Interesting stuff....
I didn't know it was knee pain that drove recumbent riders to try short cranks.

Depends if the issue is reps or load...

...to which I would add angle (in any plane) and over-reaching.
My experience is limited to uprights, where in very many cases knee pain can be eliminated by putting the saddle in the right place, spinning the gear, and stretching.
Its interesting to think about crank length, cadence and gearing in relation to road speed and rider effort, but foot speed must come in there as well.

..........Relevant biomechanical factors might include the fact that I'm not very flexible, and the fact I do a lot of running (with a less knee flexion on average than turning 170 mm cranks requires, I suspect).

The knee problem has never affected me riding uprights, and I don't feel any urge to try short cranks on them. There does seem to be biomechanical differences riding recumbent vs upright - for example on the bent I do much better with cleats positioned much further back in the shoe, to the extent that I have different shoes set up for upright and recumbent riding. .......

The reference to running is interesting, I remember watching Steve Ovett and Seb Coe in the same races, where Coe's stride was very much shorter than Ovett's......on the occasions that Coe beat Ovett, Coe's foot speed must have been higher.
I used to position my cleats so the ball of my foot was over the pedal spindle (BOFOPS?) until I read Steve Hogg on the subject https://www.stevehoggbikefitting.com/bikefit/2011/04/power-to-the-pedal-cleat-position/ and now I am more comfortable with the ball of my foot 5 or 10mm in front of the pedal spindle. On some shoes the cleats won't go much further, but i have wide feet and they don't reach the front of the shoe.

I don't fully understand the reason recumbents give more knee pain apart from the extra weight of them. Surely the distance to the bottom bracket is identical to a diamond frame? Is it something to do with KOPS? I've not checked mine.

You can exert substantially more force on the power stroke by pushing against the seat, possibly even unconsciously - if you do that on a DF, you just rise up out of the saddle. I suspect that is my problem on the Fuego and that the rapid cadence and shorter power phase reduces the knee loading. I don't get it so much on my Trice, which has a mesh seat (more complaint?), compared with the rigid GRP seat on the Fuego

On an upright, "forcing the gear" I'm pulling on the hoods, pulling back on the pedal at the bottom and forward at the top. When i get out of the saddle, I'm pulling on the hoods as well as pushing against my body weight. For racing on an upright the saddle is (generally) set further forward than an old man like me uses, so the rider's weight is forward onto their hands, and the upward reaction from pedalling supports the torso.