Crude but effective adjustable cranks

I saw this today on a disabled person’s tricycle. By the look of things, the crank can be adjusted to a variety of lengths.

Folding crank.jpg

I’ve never seen that before.
A different angle for a different crank length, right?

You think we should tell Dakoroman?


I don’t know why, but I imagine it requiring weight to be pushed in a different direction on the pedal in order to rotate all the way around. I just can’t wrap my head around it.

But they ARE the brilliant idea.

Ok, I’m going to make some of these. I won’t make them adjustable to any length but instead I’ll have slots in the junction so that they only go to specific lengths.

I can imagine that it would be slightly awkward to have different crank lengths on each side:p

The pedal is still in a straight line away from the axle, so it’s OK. However, this introduces a whole new kind of pedal bash: crank bash. On the shorter crank lengths, the crank could jut out further than the pedal, and hit objects while riding.

It’s probably really weak, too.

Yes. This is way simpler than his idea. He probably won’t check this forum, but I’m sure he posted his email somewhere.


So simple. Ow, my head. In order to figure this out, I would have had to be thinking about adjustable cranks while installing a door or something.

The only time I ever thought about adjustable cranks was whilst reading Dakoroman’s thread. I was thinking half thickness crank parts bolted together, but decided that the difficulty of adjustment was nearly equal to simply changing cranks.

torque is rotationally related in a way that makes the distance from the center of the pedal spindle to the center of the axle the distance that matters, the look of the crank does not matter… it could be a C shape.

if you had a good way to lock the adjustment at certain angles it would be a great way to make an adjustable crank.

We could be witnessing the birth of what will be an essential piece of 36er equipment. Kudos to Mikefule for spotting it and being quick-witted enough to get a pic. Now, if only someone could figure out how to make them adjustable on-the-fly while riding!

This is something I have been mulling over for quite a few months now. I think I have worked out not only how to get them to adjust on the fly, but to automatically adjust based on speed. As soon as I’ve got a bit of spare cash I’m hoping to get some samples built up, but if I get the time, I might put some drawings up on here too.


Al Lieffring made some like that a few years ago. He tried to sell them but couldn’t make them for a price anybody was willing to pay - he got a bit angry about it from what I can remember.

The thread is here


Looks like all the pictures are dead in that thread I linked to.

Here’s pdc’s for sale thread with some pics.

And here’s the fight that broke out over them :roll_eyes:


Wow! How much cash do you need?

How much you got? :stuck_out_tongue:

…And as long as there are people out there who believe there will be cranks that are adjustable, yet not weigh three times as much as regular cranks, and not cost hundreds of dollars, and be strong enough to handle road riding with a few bumps, people will keep plugging away at figuring out how to do it! :slight_smile:

Dakoroman’s ideas seem to revolve around increasing mechanical advantage using levers / pulleys / etc. Dunno that he’d bite on this idea… especially since he didn’t come up with it. :smiley:

Is this like your brilliant idea called “flux”, or your brilliant road handlebar idea which never saw the light of day.

I get the impression that your ideas are about as brilliant as black holes.

Why not just make a hub with multiple gears? I mean bikes don’t change crank sizes but just change gears (usually).

Because now you can have a geared hub with adjustable cranks for crazy-riding madness!

We have a hub with multiple gears, but that’s a much more difficult engineering problem, which means it’s more expensive and more failure-prone.

If you think the cranks won’t get built, it may be worth sharing your ideas with Semach The Monkey. That way they could get incorporated in his design and still see the light of day…

Or share them with the community for more input so they either stand a better chance of being built, or saves a non-working prototype being invested in :slight_smile: