[python] Re: Python/Hipparion Trike
- From: George Durbridge <gdurbrid@xxxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: 06 Jan 2006 20:51:51 +1100
On Thu, 2006-01-05 at 07:44, Christoph Falkner wrote:
> Thanks to Dirk, Jürgen and Jukka for advice! I think I keep
> the wheelbase at 1050mm. Still quite short, I will sit very
> near to the front axle because of the 16 inch frontwheel and
> hope the relation between front length (pivot to front axle) and
> rear length (pivot to rear axle) is ok for a stable ride. I
> expect to have 2/3 of the weight on the single front wheel
> (without luggage) - good conditions for a solid braking power
> only with front brake.
This is unnecessary and may lead to the trike tipping in corners,
particularly under brakes, downhill. Its resistance to overturning
sideways depends on the height of the centre of gravity, the width of
the track and how far forward the weight is in the wheelbase.
Why it is unnecessary to sit so far forward: one effect of braking is to
transfer weight forward from the rear wheel(s) to the front wheel(s).
This can lead to the rear wheels being lifted from the road. It means
that most braking effort is applied through the front wheels, even if
the static weight distribution is biased towards the rear. All bikes
and all cars have their main brakes at the front. The lower and the
further back the centre of gravity is, the more braking acceleration is
possible before the rear wheels are lifted from the road.
Why it is dangerous: the contact patches of the three wheels make a
triangle on the ground. The trike is stable, so long as the resultant
of the forces acting through the centre of gravity meets the ground
within that triangle. The main forces are gravity (downwards),
centrifugal force (to the outside of a corner) and the reaction to
braking (forwards).
You propose a fairly low centre of gravity, but you will put the weight
a long way forward, and the track will be fairly low.
That will put the weight above a fairly narrow portion of the triangle.
When you add a moderate sideways force from cornering, the resultant sum
of those vectors will soon fall outsde the triangle, and over you go. If
you apply the brakes at the same time, you will add a forward vector, so
that the resultant meets the ground at a point where the triangle is
even narrower than directly below the centre of gravity.
Consider putting the seat between the rear wheels, as far back and as
low as you can make it, for safety's sake. There is plenty of room to
sit between wheels 600mm apart.
> But - what´s about stability when braking hard with a Python/Hippo
> only by front brake?
It will probably be OK. Esko Meriluoto seems happy with the brakes on
the original Hipparions. Tadpole trikes generally have only front
brakes. And with the weight distribution you propose, plus forward
weight transfer under brakes, most of the braking effort will come from
the front brakes, even if you fit and use rear brakes. Rear brakes
might be useful to take some of the heat from long descents.
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