----- Original Message -----
From: "Dirk Bonne" <dirk_bonne@xxxxxxxxxx>
To: <python@xxxxxxxxxxxxx>
Sent: Tuesday, May 10, 2005 10:26 PM
Subject: [python] Re: max downhill speed --lost mail, second try
The flevoracer with 28" wheels has been reported to have "strange" high speed effects. That´s why they build it now with 26" wheels.
Aha! No my 10cents fall. Years and years ago some guy was talking about his bad experience with coasting downhill on a flevo race (he talked about not being able to control the bike). At the time, it nearly brought me off the idea of building a flevo. But when I finally build mine (20" sized), I never ever experienced anything wrong.
I could not understand why he had problem while I had none. ...never went over +-65kmh though, so may be the problem would also have been there on my bike, but I just never went fast enough.
Do you have pointers to info about this? I mean when they came unto the idea of making the wheel smaller, they probably also understood what was going on.
May be this effect has nothing to do with the trail being negative. But just that on centered steered bikes the effect is stronger ---just like that loading heavy bagage on a centered steered bike is immediatly felt.
Hi Dirk,
I found the postings about this flevoracer issue in the flevofan mailinglist:
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From: "Koen Van den Bergh" <koen@...> Date: Tue Nov 9, 2004 6:35 am Subject: Re: [Flevofan] Flevo statistics koen_vdbergh Send IM Send Email
On Mon, 08 Nov 2004 15:41:15 -0800, John Sisler <jsisler@...> wrote:
I think I read (on this site) that the Flevo Racer was dropped because of poor high speed stability.
At Tempelman you can still buy a racer which has 26" wheels. ( http://www.ligfietsshop.nl Dutch site)
Koen
John,
fun to read the account of your first spins on the racer!
Re. your question about actually racing a racer: I remember seeing a guy who participated in the 1 or 6 hours race at cycle vision 2000 (?) on a Flevo racer. He finished somewhere mid-field, I think. Just to show that it is in fact possible to race them...
About the 26/28 inch issue, I think the problem is in the stronger gyroscopic precession of large wheels. The gyroscopic action of a wheel generates strange and unexpected extra forces as you steer. The larger the wheel, the stronger this effect. Because of the extremely inclinated steering angle of the Flevo design, relatively large sideways rotations are necessary even for small corrections. And, as you may guess: the faster the wheel spins, the heavier it is, and the larger and quicker these shifts in the axis of rotation are, the stronger these gyroscopic forces. At 45 km/h, the forces generated by a 28 inch wheel are 50% stronger in comparison with 26 inch, assuming that there is no difference in weight. See my messages 80 and 86, posted some time ago.
to calculate for yourself: http://www.gyroscopes.org/math.asp
Today's fast motocycles have much smaller wheels than those of, say, 50 years ago. Probably for the same reason.
Fokke - has just built up a nice new 28 inch front wheel - Buwalda
On Mon, 08 Nov 2004 23:14:51 -0800, John Sisler <jsisler@...> wrote:
Thanks for the information, but I'm still confused. 28" not strong enough? Why not? Is there a larger load on the wheels of a Flevo Racer compared to an upright bike?
I'm not an engineer, but I guess it's because of the different way of steering. Maybe someone else can give more information.
I know an 28" wheel can be strong too (look at the cyclocross), but a 26" with a wider rim is obviously stronger. Maybe it's the same as with the headset. The different characteristics of the flevo can be the reason for much higher forces on certain components.
Koen -correct me if I'm wrong-
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