OK, here goes. I've been intrigued by the Python for a quite a while now and a build is next on my bike building list. However my perception of the Python (having never built or even ridden one) is that it has many advantages but perhaps two major failings.
1) It is difficult to ride initially. This can be overcome by practise but has to be taken into account before building. I hypothesize that this is due to the steering geometry not providing a correcting force that increases with increased steering lock.
2) This is the big one for me, apparently there can be stability issues, particularly when coasting down hills at high speed. On one of my routes to work I can hit 48 mph and exceed or approach 40 mph a number of times. This speed is then put to good use climbing the next hill. Having a bike that I can't use fully under these conditions is a problem I hypothesize that this problem is caused by the steering geometry not providing an increasing centring force with speed. This I would find difficult to live with.
There have been suggestions for altering the steering to provide a virtual steering axis, but this solution suffers from making the front wheel move differentially with the feet which probably would cause interferences, it also adds quite a bit of complexity as the solution is often on the lines of a four bar linkage.
My solution (which I was going to keep under wraps until I had tried it out) is the following:-
Assuming the turning force on the steered wheel of a cycle isproportional to sin(steering head angle) X distance from the point of contact of the wheel with the ground
Then by introducing a second steering head that steers the rear wheel the tendency of the Python front wheel to turn away from centre at high speed can be overcome.
By having a more vertical rear steering head a smaller turning of the rear wheel is required relative to the front.
My plan is to start with a standard Python configuration but with a vertical steering head for the rear wheel. The ratio of front wheel steer to rear wheel steer I was originally planning to try at 2F:1R.
Although this idea is adds some complexity (an extra steering head and a linkage) it retains all the other advantages of the Python layout, the increased centring force with steering angle may make it easier to ride and increased centring force with speed should promote stability.
Does anyone have any comments on this? As I said I was going to try it out myself first but since I haven't had time to try it yet I thought I'd share it.
Paul Lowing ============================================================ This is the Python Mailinglist //www.freelists.org/list/python Listmaster: Jürgen Mages jmages@xxxxxxTo unsubscribe send an empty mail to python-request@xxxxxxxxxxxxx
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