Rear wheel steering
this is a sort of summary that Jurriaan Bol wrote about his article in the dutch HPV magazine 11-3 (May 1995).
Many years ago I set out to design my own recumbent bicycle.
Like so many others, when I started thinking and sketching I soon found that front wheel steering, that seems so natural in a upright-bike,
generates a lot of problems in a recumbent. Holland is a great recumbent country so I was able to consult several experienced recumbent designers.
They all told me 'we have tried it, but it just does not work, forget it!'
When I asked them what they had tried the standard response was 'everything'.
When I asked them why it would not work the answer was 'it just not stable'
I know now that they where right. But at the time I just was annoyed, nobody seemed to know WHY it did not work.
For after all, understanding why something does not work is the key to a solution.
So the main motivation for my RearWheelSteeringBikes work was to try to prove them wrong, finding out 'why not?'
would be the second best outcome.
As a conclusion to my project I published an article in 'HPV-nieuws' in 1995. In this article I tried to explain (in Dutch)
why rear wheel steering on a bicycle does not work.
Now of course there are stories of RearWheelSteeringBikes's actually being ridden. They are probably true.
Actually I drove one around the house block myself. (the block was 500 m with lots of curves and bumps). But I only succeeded once
or twice in doing the entire block without stopping.
The point is, driving a RearWheelSteeringBikes is like driving a onewheeler. Yes it is possible but no, it is no substitute for a real bike.
You just cannot use it to travel from A to B.
Now, why is it different?
I discovered you have to distinguish two phases is cycling stability.
Also some behaviours in geometry that are felt in the dynamic stage are different. When it leans over in a corner
a ForeWheelSteeringBike shifts the contact area between road and frontwheel forward.
- From standstill.
We talk about the first 10 meters or so.
At first no dynamic processes are involved. It is just a matter of static balance. Very much like you can balance a broom upside down
on the tip of your finger by moving your finger below the broom's centre of gravity every time the broom begins to fall.
What you do on a bike is much the same. By changing the angle of the steer one can shift the contact point of the front wheel
and the road sideways.
Together with the shifting of ones weight sideways this enables a cyclist to get started.
(It is typical to observe people doing just that on take off. This especially visible with beginners)
- Once moving things get different. Dynamic processes kick in. Mass moving and wheels spinning.
The problem is that it is possible to design a bike that mimics the behaviour of a ForeWheelSteeringBikes in stage 1 OR in stage 2.
Never in both. So you either have a bike that is reasonable to ride (though extremely tiring) but impossible to get going.
Or you have a bike that is fairly easy to get started, but absolutely unstable and hazardous to drive.
This increases the radius of the turn. (wider turn)
Thus requiring the driver to steer more to maintain the intended radius. This is a process that no cyclist is aware of.
What it comes down to is that a turning instruction is dampened. A ForeWheelSteeringBikes does exactly the
opposite this means that when you steer into a corner the minute you lean over the bike dives into the corner. If you
are not trained to correct you simply fall. It takes all your attention to just make it through a corner.
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