Wednesday, July 02, 2008

Inspector Gadget

OK - another pictorial adventure coming up for your viewing pleasure.

I recently reported on getting a dedicated bike leg attachment made up. Some aren't exactly sure what that means, so let me show you....

First we start with the leg I have today, set up as a normal walking leg.

If we zoom in to look at the special clamp at the bottom of the socket (the large black carbon fibre part that my legs fits inside of), you can see a number of allen key bolts secure the pipe section to the socket.

These can be loosened to remove the lower pipe section which has a foot attached at the other end.

Here you can see the two parts normally hidden from view, showing the unique block style clamping system. There are four of those allen bolts, one on each side and they enable you to adjust the angles at which the pipe section fits onto the socket.

As long as I only ever undo two of these bolts (must be next to each other and not opposite) then the attachments will always clamp back on in exactly the same place each time. If I loosen three bolts, the the positioning changes. Hence I have put some loctite on the two bolts I don't intend to undo.

Here is a picture of the walking foot attachment and my cycling "foot" attachment. As you can see, there is no foot for the cycling leg. It is simply a pedal cleat attached to an adapter plate right under the end of the pipe. This enables direct force transfer down through the leg, the socket, the pipe section and onto the pedal.

Here is a picture of the cycling leg attachment connected to the socket.

On Monday I visited my good buddy, Steve Hogg at Steve specialises in fitting bikes to people. So away I went and we worked on getting the bike leg attachment adjusted for length and all the multitude of angles you can adjust. Indeed it's almost as if there is too much adjustment available!

The best part was that we discovered that my knee was able to cope with using a 155mm long crank arm. At the moment I have a short 100mm crank on the bike, as I hadn't been able to bend the knee enough to use a longer crank. On my road bikes I normally use 175mm cranks and on the track I use 170mm. So my leg has improved enough so that I am not far away from using a full length crank.

That is really important as it means I will have a much greater ability to get power through to the pedals.

All I need now is a 155mm crank arm. I have a buddy looking into that for me (he made the short crank up for me), although I know there are manufacturers of cranks that small, normally designed for BMX riders, so I'm pretty sure finding one won't take long.

Then I expect to graduate to 160mm, 165mm and hopefully at least 170mm cranks.

Ultimately I would really like to have a dedicated cycling socket, so I can simply transfer from a walking leg to a cycling leg without having to bolt things on and off. Also, the design of the walking leg socket is not quite ideal for the way I pedal the bike - there are a large number of dynamic factors at play but basically the lower socket shape angles outwards when it would be better if the line between the knee, lower socket and pedal was aligned. It will certainly do for now though.

The best way to make sure that happens is to keep riding!


Blue Eyed Samurai said...

A beginner cyclist here, stumbled across your blog looking for other cycling blogs. Am absolutely floored and awed at your positive outlook and dedication. You're an inspiration.

Kevin said...

Good on you mate. I got back on a bike for first time yesterday after 16 years, AK but the one thing I can't find is some simple click device to give me toe in to stop my heel knocking the crank. V frustrating. Any ideas from your network, i'm a casual cyclist so 1 leg does all i'm afraid so needs to be practical.
Setting up wise do you how much hyper extension do you recommend, full leg or partial, i am trying to figure out best seat height.

Alex Simmons said...

Thanks Kevin.

Have you tried using a cycling shoe and pedal/cleat arrangement?

You clip into the pedal (bit like a ski binding). Then it's simply a matter of adjusting the cleat so that your foot is pointing the right direction once clipped in.

As for leg length, while I can't specifically say for AK athletes, the rough rule of thumb is for your leg to be fully extended when your heel is resting on the pedal at bottom dead centre. That way when your foot is on the pedal in a normal pedalling location (with pedal under ball of foot or thereabouts), your knee should still have some bend at bottom dead centre of pedal stroke.

The main thing is to try to keep the hips stable. If seat is too high, it will tend to exacerbate the rocking of the hips from side to side.