[python] Re: Jetstream
- From: Stephan Schöling <stephan@xxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 28 Feb 2007 19:38:48 +0100
It took over 1 hour to read that ;-)
May i try to summarize with easy words, please correct me if i'm wrong.
The frame itself isn't stable, the frontpart flops sideway (by gravity).
The self-centering effect works against that, is making the bike stable.
If I put some weight to the seat (gravity too), i increase the
self-centering effect.
My python frame (without rider) balances at ca. 8 kg on the Seat.
(Borderline between the two effects)
The riders weight increases the self-centering effect.
The pivot angle decrease: increase wheel flop, increase self centering
(up to a point). (we still have to find the proportion)
neg trail increase: probably not much influence on wheel flop, increase
self centering.
Luggage placed near the rear wheel doesn't have much effect to the
stability of the bike, because its away from the SBB.
Dirk:
You wrote, your formulas are wrong ?
What is wrong with them ?
Stephan
dirk.bonne@xxxxxxx wrote:
Thomas P Jahn wrote:
There is a borderline where the self centering force compensates the
"weight of front part + leg-feet weight (i.e. that what causes wheel
flop)".That is where the balance is.
I am still confused about the "compensation" or balance. What exactly
has to be compensated?
Uhm, the flopping of the front part. Self centering compensates the
tendency for the front part to flop over.
Turning makes the front part come out of its left-right balance and
gravity will pull it down. That is the wheel flop. Self centering
counteracts wheel flops, giving the tendency for the bike to
straighten up. You tried Torbens bike you certainly noticed that when
not sitting on the bike how unhandable the bike was, but once sitting
on the bike the bike straightent up.
The borderline is where the tendancy to flop is compensated by the
tendency to straigthen up.
Jürgen writes on his homepage:
"*So 63° is the best pivot angle?**
*Not really, but it is close: The optimal pivot angle is exactly the
one where the weight of the whole front part (including the riders
legs) is in equilibrium with the rest of the bike (including the rest
of the rider). This is different with every bike and rider. To be
more exact: It is the angle where the wheel flop effect is nullified
by the seat rising effect.
Yes that is this borderline I am talking about. I do not agree with
the 63degrees though, as trail aspect is left out.
* angle decrease: increase wheel flop, increase self centering (up to
a point).
* neg trail increase: probably not much influence on wheel flop,
increase self centering.
The heavier the rear part is in relation to the front, the closer the
pivot angle may approach the desired maximum seat rising angle. "
Not sure I understand that.
So, here it sounds as if the compensation is to increase rear weight
versus front weight.
Moah, I would not say it like that. There is not a real choice anyway.
And how would it in theory relate to the pivot angle?: The heavier
the rear part compared to the front, the more shallow the angle may be???
But you Dirk say something about pivot angle versus front weight. And
that is probably something that cannot be put in numbers. like degree
angle / kg weight???
What could be done for a reasonable weight distribution calculate a
graph that plots the borderline pivot angle in function of the trail.
I made some formulas in the past that could aid in this, as they can
calculate the seat rise for all the input parameters. But alas the
formulas are wrong :-(
To increase the confusion:
In the other thread "81 inseam" you just said that you did not
experience any difference with the luggage. So, weight plays no role??
luggage = 14kg. that is not so much. I should not have said the word
heavy. I was more thinking on wind effects. I was just agreeing with
25Hz-es point.
Weight to the rear of the bike does have an adverse effect, but has
nothing to do with wheel flop. When you have a lot a weight on the
*far* rear part your bike gets wobbly. Every bike has that effect,
python much.
Then again its sounds as if you on your babypython must be close to
wheel fleep. But still it never happened. That sounds really good.
And your pivot angle is 60° as I can see from the survey. What about
the weight (rear versus front?) Or does it matter at all in your
case??? It seems not!?
On my flevo I can ride without steering damper at all. Without
steering damper the flevo with its positive trail has such a big
flopping tendancy that the front part litterally bangs to the ground
if you take your feets from the pedals. I find I can ride the flevo
even comfortably. I guess it is all what one is used to.
more confusion
Dirk
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