[python] Re: max downhill speed --lost mail, second try

  • From: "25hz" <25hz@xxxxxxxxxx>
  • To: <python@xxxxxxxxxxxxx>
  • Date: Fri, 6 May 2005 22:36:37 -0400

So, when coasting downhill at speed, a few things seem to be happeing.  In
no particular order . .
- your pivot angle starts to flatten out relative to the direction gravity
is working on, namely straight down.  So, as mentioned in the python stats,
the larger the angle, 70 degrees or more, the "lighter" the steering feels,
which is likely not a good feeling at speed, when you are normally used to a
"heavier" feel.
- when pedalling, on any grade of road, the friction is in front of the
pivot, pulling, and this helps keep the python wanting to run straight and
true.  When coasting on a downhill, now, the fricion on the front tire is
pushing backwards, TOWARDS the pivot.  The faster the coasting, the higher
the friction gets, and at some point the friction pushing backwards likely
approaches the ability of your weight to keep the pivot at it's lowest
point, and keep the bike running straight, with the comfortable/normal
"heavy" feel to the steering input.  This friction on the front wheel, it
would seem, will try to dissipate or reduce itself by rotating the front
wheel around and behind the pivot - which likely also adds to the creepy

What is the effect of continuing to pedal to try to keep some "drive" going
into the front wheels contact patch while simultaneously riding the rear
brake a little?  While it can't fix the reduced pivot angle due to the
hill's angle, it might put the pivot under tension by pulling ahead of the
pivot, and dragging behind the pivot to artificially increase the "weight"
on it?

> Hi,
> Yesterday I went along a tour around the Øresund, and had the chance to
> test the maximum downhill speed.
> Well it lies around 55 - 60kmh. After that it gets really scary.
> This is a little disappoining as I had hoped that with the smaller trail
> the limit would be well beyond the speed range I personally would want
> to reach. 60kmh however is at the border of that range.
> I have been groping for words to descirbe the feeling at the speed. Mind
> you, it doesn't come suddenly. It slowly builds up as speed goes up. But
> first at 50kmh it really gets your attention ;-)
> Seen from an observer nothing wrong can be noticed. The bike does not
> sway. The bike does not schimmer, or vibrate. Nothing of that.
> The feeling  on the bike is that the steering is in some way
> "activated". At least I get the feeling that when something happens I
> won't be able to correct it. And the consequence will have an explosive
> effect.
> It is like something in the steering is *acting* to fast for me to react
> to, and I doubt very much that braking in the rear would help at all
> (except bringing the speed down).
> On that trip of about 130kms I had the chance to compare the bicycle 5
> other "normal" recumbents. And the python -wich I control fully now- is
> in no way a lesser bike then the others -apart from my downhill max
> speed. At speed or manouvarability or climbing, everything works at
> least as good. I the case of manouvarability I sometimes had the
> impression I could easier slip and slalom than normal steered bike (my
> effective turn circle is 2.5m diameter).
> Dirk


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