"Death Wobble" descending question

[Borrall Wonnell]

A recent thread got me thinking about this, particularly because I own
a bicycle that is notorious for the problem...the Giant TCR
(composite).

When I descend, I usually stretch out and take my weight off the
saddle, keeping the pedals level and my back as flat as possible. On
smooth sections, I often remain on the saddle and continue pedalling.
Either way, I do not experience any sort of 'shimmy', front or rear.
No problems at speeds up to 85 km/h (53 MPH). The only time I get an
indication of a problem is if I am so far forward that no part of me
touches the saddle.

For those who do experience a wobble, is your position on the bike
significantly different than what I describe? Maybe I'm doing it wrong
I would be considered a large rider by most (6', 35" inseam, 190
lbs), and I'm using a large frame.

 

[Michael Warner]

On 19 Jul 2006 11:20:45 -0700, Borrall Wonnell wrote:

> For those who do experience a wobble, is your position on the bike
> significantly different than what I describe? Maybe I'm doing it wrong
> I would be considered a large rider by most (6', 35" inseam, 190
> lbs), and I'm using a large frame.

I have a large TCR, and I never have problems regardless of my position.
However, a smaller, lighter friend did initially have this problem with the
medium TCR, as well as a carbon Bianchi, and we established that it was
because he gripped the bars too tightly. His position made no difference.

It hadn't caused shimmy on his previous alloy bike, but he had to learn
to loosen up and relax on carbon frames.

--
Home page: http://members.westnet.com.au/mvw

 

[rsquared]

Borrall Wonnell wrote:
> A recent thread got me thinking about this, particularly because I own
> a bicycle that is notorious for the problem...the Giant TCR
> (composite).
>
> When I descend, I usually stretch out and take my weight off the
> saddle, keeping the pedals level and my back as flat as possible. On
> smooth sections, I often remain on the saddle and continue pedalling.
> Either way, I do not experience any sort of 'shimmy', front or rear.
> No problems at speeds up to 85 km/h (53 MPH). The only time I get an
> indication of a problem is if I am so far forward that no part of me
> touches the saddle.
>
> For those who do experience a wobble, is your position on the bike
> significantly different than what I describe? Maybe I'm doing it wrong
> I would be considered a large rider by most (6', 35" inseam, 190
> lbs), and I'm using a large frame.

I have had this happen on a steel frame. Don't be took quick to
dismiss the usual suspects - - improperly adjusted headset?

rsquared

 

[[email protected]]

Borrall Wonnell wrote:
> A recent thread got me thinking about this, particularly because I own
> a bicycle that is notorious for the problem...the Giant TCR
> (composite).
>
> When I descend, I usually stretch out and take my weight off the
> saddle, keeping the pedals level and my back as flat as possible. On
> smooth sections, I often remain on the saddle and continue pedalling.
> Either way, I do not experience any sort of 'shimmy', front or rear.
> No problems at speeds up to 85 km/h (53 MPH). The only time I get an
> indication of a problem is if I am so far forward that no part of me
> touches the saddle.
>
> For those who do experience a wobble, is your position on the bike
> significantly different than what I describe? Maybe I'm doing it wrong
> I would be considered a large rider by most (6', 35" inseam, 190
> lbs), and I'm using a large frame.

I get front wheel shimmy on my Waterford 1200 58cm and Litespeed
Tuscany 59cm at about 28mph when I coast with no hands on the bars.
Every time. I stop the wobble by either putting my knee against the
top tube, or putting my hands back on the bars. With hands on the
bars, I've had the Waterford to 60mph without shimmy. Litespeed only
to mid 40s since its new and when in the mountains a week ago the
weather was rainy on the descents so I did not think it too wise to try
for any speed records. Due to a bit of sanity and self preservation
instincts, I haven't tried to take my hands off the bars at speeds
significantly above 28mph to see if the shimmy does not appear outside
of a the 28-35mph speed window.

Wheel shimmy is due to the frame and rider combination.

 

[Borrall Wonnell]

> Wheel shimmy is due to the frame and rider combination.

Thanks for all the comments! Riding without hands on the bars is not a
skill I'm 100% comfortable with yet, and that isn't helped by the road
conditions around here.

Cheers,
Dave

 

[[email protected]]

Borrall Wonnell wrote:
> > Wheel shimmy is due to the frame and rider combination.
>
> Thanks for all the comments! Riding without hands on the bars is not a
> skill I'm 100% comfortable with yet, and that isn't helped by the road
> conditions around here.
>

It is possible you have an overtightened/damaged headset which may be
making you be uncomfortable with no hands. This could also make the
wobble worse, or more frequently apparent. I used to get wobble on my
old steel frame, and was likewise not comfortable no-handed until I
replaced the pitted headset. And I used to be very good at no hands. I
once completed a century riding about 95% no hands due to a cast on my
arm that was very uncomfortable using bars. With a pitted or overtight
headset, riding no hands is very, very difficult.

If you have a well balanced fore-aft position on the bike, riding no
hands even on lousy pavement shouldn't be too difficult. If you are
unable to remove you hands from the bars without using too much back
muscles, and straining, you may have a riding position too far forward
with too much weight on your hands. This could cause all sorts of
problems.

Joseph

 

[john]

[email protected] wrote:
> Borrall Wonnell wrote:
> > A recent thread got me thinking about this, particularly because I own
> > a bicycle that is notorious for the problem...the Giant TCR
> > (composite).
> >
> > When I descend, I usually stretch out and take my weight off the
> > saddle, keeping the pedals level and my back as flat as possible. On
> > smooth sections, I often remain on the saddle and continue pedalling.
> > Either way, I do not experience any sort of 'shimmy', front or rear.
> > No problems at speeds up to 85 km/h (53 MPH). The only time I get an
> > indication of a problem is if I am so far forward that no part of me
> > touches the saddle.
> >
> > For those who do experience a wobble, is your position on the bike
> > significantly different than what I describe? Maybe I'm doing it wrong
> > I would be considered a large rider by most (6', 35" inseam, 190
> > lbs), and I'm using a large frame.
>
> I get front wheel shimmy on my Waterford 1200 58cm and Litespeed
> Tuscany 59cm at about 28mph when I coast with no hands on the bars.
> Every time. I stop the wobble by either putting my knee against the
> top tube, or putting my hands back on the bars. With hands on the
> bars, I've had the Waterford to 60mph without shimmy. Litespeed only
> to mid 40s since its new and when in the mountains a week ago the
> weather was rainy on the descents so I did not think it too wise to try
> for any speed records. Due to a bit of sanity and self preservation
> instincts, I haven't tried to take my hands off the bars at speeds
> significantly above 28mph to see if the shimmy does not appear outside
> of a the 28-35mph speed window.
>
> Wheel shimmy is due to the frame and rider combination.

Were you using the same set of wheels on both frames?

Regards, John

 

[Chris Z The Wheelman]

"Death Wobble". I like that term, much more descriptive than "shimmy"
which sounds more like a dance. LOL

- -
Comments and opinions compliments of,
"Your Friendly Neighborhood Wheelman"

My web Site:
http://geocities.com/czcorner

To E-mail me:
ChrisZCorner "at" webtv "dot" net

 

[Borrall Wonnell]

> It is possible you have an overtightened/damaged headset which may be
> making you be uncomfortable with no hands. This could also make the
> wobble worse, or more frequently apparent. I used to get wobble on my
> old steel frame, and was likewise not comfortable no-handed until I
> replaced the pitted headset. And I used to be very good at no hands. I
> once completed a century riding about 95% no hands due to a cast on my
> arm that was very uncomfortable using bars. With a pitted or overtight
> headset, riding no hands is very, very difficult.
>

OP here. I gave no hands another (brief) shot at around 10 MPH. No
problems with shimmy, but I still need practice. The shimmy I get only
occurs when my weight is shifted forward (out of saddle, not
pedalling)...in this position, I doubt I could let go of the bars and
not fall over

The bike hasn't been crashed and the steer mechanism still seems smooth
after 2 years. I haven't pulled the fork to inspect the headset
(internal type). I think hands-free is purely a function of practice
on my part, given the condition of the bike.

Cheers,
Dave

 

[David L. Johnson]

On Mon, 24 Jul 2006 04:11:34 -0700, Borrall Wonnell wrote:

> OP here. I gave no hands another (brief) shot at around 10 MPH. No
> problems with shimmy, but I still need practice. The shimmy I get only
> occurs when my weight is shifted forward (out of saddle, not
> pedalling)...in this position, I doubt I could let go of the bars and
> not fall over
>
> The bike hasn't been crashed and the steer mechanism still seems smooth
> after 2 years. I haven't pulled the fork to inspect the headset
> (internal type). I think hands-free is purely a function of practice
> on my part, given the condition of the bike.

No, not really. Such a shimmy can occur with any rider, given the right
combination of position, bike, and incline. It is a set of coincidences
that produces resonance. Changing any piece of it will change the
resonant frequency. Those who do not experience shimmy are those for whom
that set of coincidences doesn't occur in their riding. For example, a
stiffer frame might move the resonant frequency up some, so that one would
have to go 60+ mph to experience it. Since few of us go that fast, and
those who do (or claim to) only hit such speeds occasionally, for short
timespans, shimmy will not be likely to occur.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems.
_`\(,_ | -- Paul Erdos
(_)/ (_) |

 

[[email protected]]

> > I get front wheel shimmy on my Waterford 1200 58cm and Litespeed
> > Tuscany 59cm at about 28mph when I coast with no hands on the bars.
> >
> > Wheel shimmy is due to the frame and rider combination.
>
> Were you using the same set of wheels on both frames?

Not the exact same but similar wheels. 32 hole, 3 cross, 14/15 DT or
WS spokes, Mavic Open Pro rims, Chorus or Record hubs.

Waterford with 1999 Campagnolo Vento wheels does not shimmy in the
28-35mph speed with no hands. Have not tried the Vento wheels on the
Litespeed. Nashbar aluminum frame bicycle does not shimmy with the
aforementioned 32 hole Open Pro wheels in the 28-35mph speed with no
hands.

So I'll restate my comment to "Wheel shimmy is due to the frame and
wheels and rider combination."


>
> Regards, John