Changeable crank length

I’ve just found this Crank Arm Shortener and thought it might be of interest here. I’ve not tried it but saw one in the LBS. Price: $100USD is the best I saw on-line and in the LBS.

it’s available in the Quality Bike Parts catalog, so just about any LBS can order it. they will, however, increase the “Q” factor of your cranks.

Took me a while to figure out how they worked from the dimensions page; the assemlby page made it a bit clearer-

Interesting that they’re designed for a different function:-

“TANDEMS - Crankarm Shorteners are a device that allows an elementary age child or short adult to ride on the back seat (the stoker’s seat) of a tandem bicycle. The Crankarm Shorteners reduce the length between the stoker’s seat and the pedals. Briefly, the pedal is removed from the crankarm, the Crankarm Shorteners installed and the pedals are then reinstalled on the Crankarm Shortener.”

ie the adjustment is so those with short legs can use the bike, rather than the leverage change that unicyclists would want them for; but, the result is the same.

Re: Changeable crank length

That’s quite a profit margin… from the designs it looks to be about $12 in aluminum stock and 2 or 3 $1 bolts per crank.

For that much money you’re better off buying two sets of cranks and swapping 'em out with one bolt each.

This design might not stand up to the strains induced by trials riding… I’m curious, why are you interested in these?

Re: Re: Changeable crank length

If that’s the case, why don’t all cranks cost less? Normal cranks use even less material.

Anyway, I don’t think anyone would use these for trials. To start with, they must be heavier because of the added material used to make it adjustable. I have always thought that road use is where adjustable cranks are the most useful.

It took me a while to understand how these cranks work. Now that I think I have a grasp on that, I wonder how well they work.


If i remember rightly, Nathan Hoover has adjustable cranks…might be worth talking to him about them?

Re: Re: Re: Changeable crank length

I bought some 7075-T6 to make some beefy MUni cranks, the same material used in the Odyssey Black Widows and Kooka Kranks. The cost for six cranks came out to less than $10 per crank.

In higher quantities, the price breaks might bring the cost down to $6 or $7 each, unless the manufacturer has the stock cut up at the supplier, add (worst case) $1 each there.

The rest of the cost goes to paying the machinist, renting / leasing the CNC machine and covering other overhead. Machinists charge a hefty hourly wage, and CNC machines aren’t something you can just buy off eBay…

I’d say if people bought cranks like they bought soda pop, we’d see the prices on these things plummet. But until then we should just gloat that we’re (collectively) pushing the edge of cycle sports… we’re breaking everything the industry is making, so we’ve gotta pay for them to develop better products!

Yes, he does. However, they cost something like US$500. Bronson Silva also has cool adjustable length cranks on his titanium suspension Coker.

There is a past thread on some adjustable crank ideas: Adjustable crank idea I like the eccentric crank that Steve Howard drew up in his CAD system. It just seems like a neat design. It’s similar in design to the cranks that Bronson Silva has on his Creative Gecko bionic Coker.

Here’s a link to Steve Howard’s gallery of two adjustable crank designs he drew up: Adjustable cranks gallery