Steering oscillation ... what to do?

carlfogel@comcast.net

On Sun, 15 Jun 2008 13:57:37 -0500, A Muzi <am@yellowjersey.org>
wrote:

>carlfogel@comcast.net wrote:
>> On Fri, 13 Jun 2008 19:53:20 -0700 (PDT), carlfogel@comcast.net wrote:
>>
>>> On Jun 13, 5:28 pm, "Mike Jacoubowsky" <Mi...@ChainReaction.com>
>>> wrote:
>>>
>>> [snip]
>>>
>>>> A bicycle isn't inherently stable; if it were, you
>>>> could give it a push and get it to head down the road a ways. In all cases
>>>> (with normal bikes) the bike is dependent upon rider input for stability.
>>>> Which is a problem, since a nervous rider does things that reinforce a
>>>> tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits hard
>>>> enough on the fact that a bicycle is inherently unstable until you add a
>>>> person to it. That should be enough to get people thinking in the right
>>> [snip]
>>>
>>> Dear Mike,
>>>
>>> Like you, I thought that a riderless bicycle was inherently unstable
>>> and would topple over shortly after being released.
>>>
>>> Several posters enjoyed setting me straight with movies like this:
>>>
>>> http://ruina.tam.cornell.edu/resear...e_stability.mov
>
>> Aha! An email suggests that the front fork may have been reversed to
>> improve stability.
>>
>> Sure enough, if you stop the movie at the start of the second run, you
>> can see that the fork is backward:
>>
>> http://ruina.tam.cornell.edu/resear...e_stability.mov
>>
>> That may account for the recovery when the bicycle is slapped
>> sideways.
>>
>> On the other hand, numerous posters have mentioned pushing bicycles as
>> kids and watching them stay upright for long distances.
>>
>> Alas, most of us aren't willing to experiment with our own bikes,
>> since the results is usually a crash.
>
>
>Usually?
>What is the other result?

Dear Andrew,

The experimenter pushes his riderless bike, lets go, runs along next
to it, and catches it before it can crash, laughing wildly.

(I once saw some little kids doing this. They didn't seem to care that
their experimental technique invalidated their results.)

Cheers,

Carl Fogel

Doug McLaren

In article <9b04be0a-13a4-4973-93cd-7a1e8d7a721b@y21g2000hsf.googlegroups.com>,
dustoyevsky@mac.com <dustoyevsky@mac.com> wrote:

| On Jun 13, 2:10*pm, "Doug McLaren" <dougmc
| +usenet-20080...@frenzied.us> wrote:
|
| > It's a Giant OCR2 2003 or so -- aluminum frame, fork. *It's pretty
| > much stock, except that it has 700x28c tires, and a luggage rack.
|
| What's on the rack, if anything?

I had a Transit Metro Trunk Bag on top of the rack with about 5 lbs of
stuff in it. It's pretty well secured.

Now, I'd forgotten that the night before, I moved the rack back a bit
to make it more level. The bottom supports I left alone, but the top
ones I extended as far as they'd go, which would reduce it's resonant
frequency.

The resonant frequency of the rack seems higher than the shimmy I had,
but then again, adrenalin messes with your sense of time so perhaps
the shimmy was faster than I thought.

Either way, I put the rack back the way it was.

I'm probably a large part of the problem. I wrecked my comfortable
Bridgestone RB-T in a fluke accident involving just the bike, the
pavement and me, and I haven't really gotten my confidence back, and
I'm still not comfortable with the new bike. So when I get outside of
outside my comfort zone (as I certainly am on this stretch of road) I
do tense up. The shimmy incident didn't help with getting my
confidence back, but now knowing why should, and I'll just have to
work on it.

Thanks for the advice, guys ...

--
Doug McLaren, dougmc@frenzied.us
Marriage is a three ring circus: engagement ring, wedding ring, and
suffering. -- Roger Price