Cotterless & Splined

What is the difference between cotterless cranks and splined cranks? I know Splined are better, but what is the difference? Is it just how they are made, or how they are put onto your uni?

more points to take stress… uhhh thats all i can tell

Re: Cotterless & Splined

Cotterless cranks attach to a square spindle/axle. This square is slightly angled and acts as a wedge as the crank is pressed onto the spindle/axle. This is held together with a nut or bolt that screws down on the crank arm.

Splined cranks attach to a splined spindle/axle. Both have a large number of grooves (splines) that are machined in them to create a tight fit that is much stronger than a cotterless crank set-up. Because of the large number of splines the axle and joining part on the crank have a larger diameter which also gives added strength to this type of set up.

Also there are (at least) two types of splines (aside from number of splines). 1:The type that are held on by a retaining nut and 2: The type that have a pinch bolt. Either case is stronger than the square beveled type. -But also more costly. Aside from the cost disadvantage, the spline on the axle must exactly match the spline on the crank.

How does the weight of a splined hub compare to that of a normal hub? All the splined hubs I’ve seen look a fair bit bigger than normal hubs, which I presume makes them stronger, but wouldn’t it also make them heavier?


i don’t have one on my freestyle unicycle.

I was curious, so I looked up “spline” in some online dictionaries. This is from


  1. Any of a series of projections on a shaft that fit into slots on a corresponding shaft, enabling both to rotate together.
  2. The groove or slot for such a projection.

There was more to it, but that’s the relevant part. So why is a splined axle better? Three main reasons I get off the top of my head:

  1. Much stronger than conventional axle
  2. Crank stays on much better than conventional axle
  3. Much stronger cranks are made for splined axles

The move to splined axles was a move for unicycles from “standard” bike parts to “high end” stuff. Now we can choose from the top available BMX and Trials equipment.

Square taper cranks have two main disadvantages. Because they are square, their effective diameter is reduced to that of a circle that just touches the flats, from the inside. So the weak point of the axle is much smaller in diameter than the axle itself. On a splined axle, the effective circle is a lot closer to the outside diameter of the axle. Then if you increase the base axle diameter, it only gets stronger.

The second weakness of square tapers is the way cranks come loose. on a bike, you pedal in one direction only. Cranks stay on. If they didn’t they would have been redesigned ages ago. Since unicycles aren’t money-makers, they use bike parts, even when the bike parts are over-strained.

Because we pedal in both directions with equal force, and constant reversals of that force, a square tapered crank arm is naturally going to be trying to work its way down the taper. It’s held in place by a small nut, and however much Loctite you can get to work. Even then, they usually come loose unless you constantly tighten them (talking about MUni here).

On my DM ATU, there is no taper in the axle. Once (in 3 years of use) I noticed one of the cranks had been slowly working its way off the axle. I tapped it back on, tightened the screw on the crank, and it hasn’t moved since.

I’d rather have a heavy axle that doesn’t break than a lighter axle that needs to be replaced. I think in the realm of BMX and Trials, even the highest-end splined stuff is heavier.