Test of SH axle

At the Cali MUni weekend, Ryan Atkins was once again willing to risk bodily harm to test equipment. In this case it is the splined axle made by Steve Howard from 17-4PH stainless steel. The interesting property of this alloy is that it can be hardened to the strength and toughness of CroMoly with an air quench so no oil is involved in the tempering process.

The picture included (Tom Blackwood’s shot) shows the drop to be of order 7-8 feet to flat with me as the height scale reference. Ryan did three drops from this height, the first one was a bounce and the second two he landed successfully. The photos from John Childs in his gallery indicate the damage. They are on the last page.

John Childs Damage Photos

The wheel is slightly tacoed, probably due to the fact that the rim had a flat spot in it last time it was laced. The cranks are no longer parallel. Visual inspection revealed nothing. Replacing the Kooka cranks (which Steve broached for me) with KH cranks showed the same lack of parallelicity. Clearly the axle twisted uniformly along its length.

I have done several 5 foot drops with this unicycle and I bounce and land like a pig more often than not. I thought this might be a better test of the rig than Ryan’s because I’m heavier and more awkward. Clearly that’s not the case and the height makes a big difference. Kris has done five foot drops on the same unicycle but he is quite light and lands like a cat so there is really little comparison there.

The test results show that I can’t possibly destroy the setup because I can’t go as big as Ryan. But the material, which is the same as the artistic axle, flange, crank combo that Lloyd received as a prize, is probably not a good choice over CroMoly especially because it is somewhat expensive. Producing an expensive, inferior product is not one of Steve Howard’s goals so don’t plan on seeing a variation of this setup in the future.

Steve and I would both like to thank Ryan Atkins and Kris Holm for participating in the drop tests. Also thanks go to John Childs and Tom Blackwood who provided the photos.

Re: Test of SH axle

The photos of the drop and aftereffects are on page 4 of the Tahoe 2004 gallery

Did the flange twist on the axle at all? If the splines under the flange twisted then the flange itself would rotate a bit. That rotation would tweak the spokes on that side of the wheel and cause the wheel to taco.

nobody bothered to check the damage to ryan’s knees/back/ankles/brain?

he is immortal


Geez. Expensive tests.

Whats that…8, 9 feet?

Is it impossible to machine the same type of hub out of chromoly?

Ryan was fine.

That was around 8’.

Machining the hub is no problem, except that the machining must be done before the hub is heat treated. From my understanding, chromoly is very difficult and expensive to heat treat, whereas this stainless steel is much easier to heat treat. I could be completely wrong, though.

Re: Test of SH axle

Wish I could take the credit for the photo, but that’s not mine. I was driving to the airport by that time, missing the great final action.


I don’t know if the flange twisted noticeably. You are certainly correct that it could weaken the wheel locally and cause it to taco.


The KH hub and axle are probably CroMoly and are mass produced. The SH axle copies the spline of the KH axle.


You are essentially correct. Mass producing would make heat treating at an outside facility relatively cheap for CroMoly because you do gobs of parts at once. The 17-4PH is extremely easy to heat treat so doing a few parts is cost effective. Machining pre-treated materials are roughly the same, the 17-4PH may be easier to machine. I thought it was very easy to machine 17-4PH but I haven’t done CroMoly, maybe Steve has.


I hate to give you any credit for something you didn’t do. I even hate to give you credit for things you actually do. You noticed how I short changed your Coker ride by 14 miles in the bike shop. Maybe it was Nathan’s photo.