## [python] Re: Jetstream

• From: dirk.bonne@xxxxxxx
• To: python@xxxxxxxxxxxxx
• Date: Wed, 28 Feb 2007 18:14:48 +0100

```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

```