High-speed shimmy problem

I have tried different wheels and tires and the problem persists on rough
roads. I have tried 28X2, 32X3 and 36X3 front wheels. The shimmy always
starts with power off (coasting and without spinning the cranks). I recover
from the shimmy by either holding on for dear life or spinning the cranks.

Now I know some readers in this NG think that everything gets smoother at high
speed and you really don't need to touch the bars in a high speed tuck (i.e.
Jobst), but give me a break I have a problem. I am not making the bike shimmy
by shivering!

My frame size is 58 cm center to center and I have a Kestral fork. My headset
does not seem to have any wear!

Help!

I will try rotating the bearing races 90 degrees. At this point I will try
anything or I will stay below 43 mph on rough roads. However, the headset DOES
NOT seem to have brindeled (sic?) races. The bike does not seem to be auto
steering. The shimmy does not occur on smooth roads. One the resonance starts
it is a wild ride.

Victor

It quits when you spin because you are softening the coupling between your
mass and the saddle. Your butt is the mass that the front of the frame is
"vibrating against" (for lack of better words). Next time, try lifting
your butt slightly off the saddle to remove the "reaction mass". When I
tried this on a bike that wobbled (another name for shimmy) the wobble
stopped instantly.

Credit to Jim P (who moderates the hardcore-bicycle-science mail-list) for
pointing this out to me. To see the effect at zero speed, lean your saddle
against something solid (like a 6x6 post that holds up the porch roof, with
the rest of the bike just standing there (not touching anything solid
except the tires on the ground). Then, give the head tube a whack
sideways, you should see the same frequency of wobble.

This is slightly analogous to hanging a ruler off the edge of the desk and
flicking it to make it vibrate up and down -- it stops vibrating if you
don't keep it held firmly against the desk.

Before you flame me -- give it a try. It's usually easy to get any frame
to wobble if you attach some mass (say 2 kg) rigidly to the side of the
head tube.

I did not notice this problem until recently. However, that does not mean that
the problem did not exist when the frame was new. As I pointed out before, the
problem only occurs coasting above 43 mph on rough roads. High speeds on
smooth roads do not create problems. Once the resonance starts, the problems
begin.

I have checked frame alignment myself (only with a fine cord and not an
alignment table like it should be done) and it seems OK. Any frame/rider will
resonate at a certain speed. Does this mean that there is something wrong with
my frame?

8.60 Shimmy or Speed Wobble

From: Jobst Brandt <jbr...@hpl.hp.com>

"Shimmy is not related to frame alignment or loose bearings as is often
suggested. Shimmy arises from the dynamics of forward motion and the
elasticity of the frame, fork, and wheels, and the saddle position.
Both perfectly aligned bicycles and ones with wheels out of plane to
one another shimmy nearly equally well. The same is true for bearing
adjustment. In fact shimmy is more likely with properly adjusted
bearings than loose ones. The bearing or alignment concept is usually
offered as a cause of shimmy and each airing perpetuates the idea.

"Shimmy, the lateral oscillation at the head tube, depends primarily on
the frame and its geometry. The inflation of the tire and the
gyroscopic effects of the front wheel make it largely speed dependent.
It cannot be fixed by adjustments because it is inherent to the
geometry and elasticity of the components. The longer the frame and
the higher the saddle, the greater the tendency to shimmy, other
things being equal. Weight distribution also has no effect on shimmy
although where that weight contacts the frame does.

"In contrast to common knowledge, a well aligned frame shimmies more
easily than a crooked one because it rides straight and without bias.
The bias force of a crooked frame impedes shimmy slightly. Because
many riders never ride no-hands downhill, or at least not in the
critical speed range, they seldom encounter shimmy. When it occurs
with the hands on the bars it is unusual and especially disconcerting.
There is a preferred speed at which shimmy initiates when coasting
no-hands on a smooth road and it should occur every time when in that
critical speed range. Although it usually does not initiate at higher
speed, it can.

"Pedaling or rough road interferes with shimmy on a bicycle that isn't
highly susceptible. When coasting, laying one leg against the top
tube is the most common way to inhibit it. Interestingly, compliant
tread of knobby tires give such high lateral damping that most
bicycles equipped with knobbies do not shimmy.

"Shimmy is caused by the gyroscopic force of the front wheel that acts
at 90 degrees to the axis of the steering motion. The wheel steers to
the left about a vertical axis when it is leaned to the left about a
horizontal axis. When the wheel leans to the one side, gyroscopic
force steers it toward that side, however, the steering action
immediately reverses the lean of the wheel as the tire contact point
acts on the trail of the fork caster to reverse the steering motion.

"The shimmy oscillates at a rate that the rider's mass on the saddle
cannot follow, causing the top and down tubes to act as springs that
store the energy that initiates the return swing. The shimmy will
stop if the rider unloads the saddle, because the mass of the rider is
the anchor about which the oscillation operates. Without this anchor
no energy is stored. The fork and wheels may store some energy,
although it appears the frame acts as the principal spring.

"Shimmy can also be initiated with the hands firmly on the bars by
shivering, typically in cold weather. The frequency of human
shivering is about the same as that of a typical bicycle frame."

I would add that I have often known shimmy to result from seriously
inadequate spoke tension, especially in the rear wheel.

Sheldon "Thanks, Jobst" Brown
Newtonville, Massachusetts
+--------------------------------------------+
| In order to understand recursion, |
| first, you have to understand recursion. |
+--------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-1040 FAX 617-244-1041
http://www.sheldonbrown.com/harris

From the high speed of onset of your shimmy, it seems that it must
also have a small excursion and that you are probably not assuming a
reasonable coasting position. You are coasting because I don't
believe that you can pedal to that speed, there being no advantage to
pedaling at that speed because you could only add 2.7mph to your speed
by pedaling, assuming you are a 25mph flat land rider.

I think I pointed out that these things do not in themselves cause
shimmy, but as an aggregate of several elasticities in the frame fork
and wheel, coupled with rider position. If you coast with your knees
pressed against the top tube (where the should be aerodynamically),
there is no reasonable way for the bike to shimmy. The length of
your bar stem also affects the interaction of your hands and damping.

I never advocated not touching the bars. In fact, that's the best way
to make a bike shimmy, by riding no-hands without the legs touching
the top tube. I suggested that one can go faster with the hands on
the stem and elbows in on the legs that are held closely together.
This ii in effect riding no-hands, but in no way takes the hands off
the bike.

Jobst Brandt <jbr...@hpl.hp.com>

Would you please explain why you believe frame alignment is causing
this. I have never ridden a bicycle that doesn't shimmy new or old.
Of course they don't do this unless I coast no-hands on a smooth road
without my legs touching the top tube. A soft front tire increases
the oscillation and lowers the onset speed a little. So from what do
you draw your conclusions, and who is "Bobby"?

Jobst Brandt <jbr...@hpl.hp.com>

A bike is a system of springs. Unless you change the stiffness,
configuration or damping of the system, there is nothing you can do
about the shimmy.

To change the stiffness, buy a stiffer frame or fork.

To change the damping, pinch the top tube with your knees.

To change the configuration of the system, change your position.
If you are sitting when the shimmy starts, stand. If you
are standing when it starts, sit.

Damon Rinard

I don't know if I could pedal to 43 mph? I was running a 119.25 inch gear and
I guess it is possible to attain that velocity spinning at 120 RPM's (at least
on paper). I agree that it would be difficult to sustain that speed. I really
think I was coasting.

My real question is what do you call a reasonable coasting position? I have
never noticed any real differances in stability from the different hand
positions. Although, I would agree top speed can be lowered by poor
positioning.

Sorry! My mistake. I finally did read your FAQ 8.60 Shimmy or Speed Wobble.
I will try resting my knee on the top tube.

> The most likely cause [of the shimmy] in your case

I don't believe that bad frame or fork alignment can cause a shimmy.
(Seems to me it would be more likely to prevent or damp a shimmy.)
Can you explain why you think it can? It's often mentioned, but I've
never heard a likely sounding explanation of the mechanism for
misalignment to cause a shimmy. This doesn't prove it isn't true, but
do you have any evidence that it is?

I've seen lots of straight frames that shimmied, and quite crooked ones
that didn't, with no clear correlation between those factors.

Mark Bulgier, Seattle
mailto:Ma...@TiCycles.com
http://TiCycles.com

Any suggestions for those who own a straight frame that has a high speed
shimmy? Is that Ti frame with the 650C wheels that I saw you on, less likely
to shimmy? Are Ti frames with long wheelbases and long top tubes more likely
to shimmy?

SNIP

> Sheldon "Thanks, Jobst" Brown

Well I guess I won't have to search for Jobst's posts any more if Sheldon's going to do
his posts for him!

Chris McSweeny
--
cpmcs...@dera.gov.uk
The views expressed above are entirely those of the writer and do not
represent the views, policy or understanding of any other person or
official body.

What, with a tow rope? That is 90-97kph. What were you
doing, driving a 56-12 down a straight 20% grade? What do you weigh?

Somewhat incredulous, Rob

...

Well, prepare to be amazed. It is quite easy to hit 90 kph
in the Rocky Mountains. Add a nice westerly Chinook wind,
and I've hit 98 kph (according to the computer, mind you).
But I have been paced by an auto at 95, so I suspect the
computer is close.

Tom

There seems to be some question about what a shimmy is and
how it starts etc. I thought that Jobst had covered that in
pretty good detail so many times that it would be in the FAQ.

A shimmy is an oscillation around the track of the bike. The natural
frequency of a bicycle frame is about that which can be excited
by:

1) the self-centering forces of the rake and trail
2) the muscle reaction of the rider
3) the 'bounce' of the tires (such as hitting a pothole etc.)

Frames that are most likely to be in the proper range to cause
a shimmy have to be straight because bent frames do not track
straight and therefore require the rider to be putting in a
dampening force all the time during the ride.

If you have a bike built of 'normal' sized steel tubing you can
easily get it to shimmy by riding with no hands on a level road
(or with a slight descent) at about 20 mph. The bike might ride
along smoothly for a bit, but the first time the tire is deflected
the self-centering forces will cause the bike to overcorrect slightly
and the oscillation will start. Pushing on the top tube with your
leg will cause it to stop. As will standing on the pedals (it's
an interesting exercise to stand without touching the bars.)

The slightest touch on the bars will immediately dampen the shimmy.

At certain speeds hitting a pothole or even getting hit by a side
gust of wind can start the oscillation. If you (like me) are too
tight on the bars, your muscles can cause a powerful self-centering
overcompensation that you could swear was really the bike. Yet loosening
your grip (almost impossible sometimes) will cause the 'speed wobble'
to stop.

Multishaped/Oversize steel bikes, aluminum frames, carbon fiber bikes
and ti seldom have these problems because the natural frequency of these
bikes is much higher and excitation is much more unlikely. It is a bit
disconcerting but once you know how to deal with it it isn't much
of a problem.

-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet

Mark Bulgier wrote:

My frame was put over 5mm of alignment at the BB (in relation to the
headtube) during a severe crash this year. The bike had been rock solid at
60 mph downhill on a number of occasions, nary a hint of shimmy. After the
crash, there was no visible sign of damage so I continued riding it, but
hadn't taken it past 40 mph. The last time I took it up over 50 mph, the
bike seemed to induce a shimmy, and also seemed like it wasn't tracking
normallyl. Thats when I sent it off to get the alignment checked and found
out of the misalignment. Based upon this experience, I can't say that
alignment is the one and only cause of shimmy, but certainly can
contribute. Unfortunately, this is based upon a real world experience and
no lab tests were done by certified technicians to provide data to back it
up.

Well, one at a time.

Sprint finishes. I have a hard time swallowing 50 MPH.
45 MPH no problem, but I think 50 is a little beyond
the envelope. This is of course on the flats.

On hills, it takes a fairly long straight steep hill to hit
50 going solo. To hit 60 you need a significant slope
for a long distance (or a tandem on a 50 MPH hill). These
hills exist, but they are far less common that people
seem to think they are.

--
Dave Blake
dbl...@phy.ucsf.edu
http://www.keck.ucsf.edu/~dblake/

Try the West side of Moniter Pass every July in the Death ride.

Eat to Ride
Ride to Eat

__O
-\<,
( )/ ( )

Dave Blake wrote:

> for a long distance (or a tandem on a 50 MPH hill). These

Dave, take a jaunt up to Napa and try going down Oakville Grade. If you
know the downhill, you can attain speeds of 60, as I have done it
several times. However, this is based upon my cyclocomputer, as I have
not had any engineers out in the field with laser based radar guns to
actually confirm if the speed is correct to the .00001 of a mph. Also
try Petrified Forest road in Sonoma County 16% grade or may Geyers at
18%. Cobb Mountain is another great downhill with 4 miles of smooth
road with an AVG of 11%. Also a nice climb. By the way, I weigh 195
lbs.

I don't think so....give me a hill where I can get on top of my 53-12
and I can get up to 55 or 56 mph and I only weigh 140 soaking wet.

: On hills, it takes a fairly long straight steep hill to hit

A long steep grade isn't necessary if you have a stong enough
tailwind. On a day when the Chinook winds were blowing near
Boulder, I hit 58 MPH on a hill that I estimate at 6-7% (feed
hill on the Morgul Bismark course). Altitude was a factor too.

Bret Wade
Boulder, CO

>I don't think so....give me a hill where I can get on top of my 53-12

You must be an amazing dude to be able to put out
enough power at 50 MPH to overcome the increased
air resistance inherent to the pedalling position
compared to the tucked position.

In fact, you could take Marty Nothstein in a sprint
easily. Pedalling does not help at these speeds
because the air resistance difference is too large.

--
Dave 'tuck' Blake
dbl...@phy.ucsf.edu
http://www.keck.ucsf.edu/~dblake/

now dave, we all know someone is perfectly capable of doing it. he may just
need the right hill.
now, as to his cyclometer calibrations... ;)

--
fast#forward# "Would she prefer it if i washed myself more often #www
.. __o # than i do? would she prefer it if i took her to an #louisville
.. -\<, # opera or two? i could disort myself to be the perfect #edu
..(_)/(_) # man. she might prefer me as i am..." -sting #/~csmayh01
cycling#team#-----------------try again, jan 1st, mtb---------------###########

> > Somewhat incredulous, Rob

Gee, that means you're "getting on top of" that 53-12 158 times every
minute, not to mention putting out some major Wattage. I suggest you
quit your job and immediately start cycling professionally.

Mark
R13884.at.email.sps.mot.com

Yes, and the moon IS made of green cheese Santa Claws.

Jobst Brandt <jbr...@hpl.hp.com>

Believe it, Rob. There are a couple of hills around here where I can get
up to 55 mph, and I don't weight all that much. One of them has a stop
sign at the bottom, which is a real drag.

There's another hill where I think I could go even faster, but so far I
have only attempted to climb it (not entirely successfully, I must
admit!). This has a *barricade* at the bottom, so I might not try it.

Adam Rice | adam...@crossroads.net
Austin TX USA | http://www.crossroads.net

> 53-12 and I can get up to 55 or 56 mph and I only weigh 140 soaking
> wet.

> MPH to overcome the increased air resistance inherent to the
> pedaling position compared to the tucked position.

In fact, assuming you are already in an upright pedaling position and
can put out the same power as on the flat, you could theoretically
increase from 50 to 52mph by pedaling. Meanwhile, in a suitable
crouch, as much as 10mph can be gained. However, since the people who
write these stories have never done this, they are not aware of how
absurd their claims ring. To sit up and pedal when coasting crouched
at 50mph serves only to slow the bicycle down no matter how briefly
and hard you try.

> Pedaling does not help at these speeds because the air resistance
> difference is too large.

Not long ago, I was passed on a flatter section of a local descent by
a young powerful rider who pedaled mightily all the way down a six
mile mild grade on which he did not prevail as I and my friend coasted
the entire distance. We did not reach 50mph.

Jobst Brandt <jbr...@hpl.hp.com>

It takes a tail wind to break 50mph on that hill.

Jobst Brandt <jbr...@hpl.hp.com>

Oh, and you were pedaling to achieve this speed? Besides, I can't
imagine a bike race finishing on this road, as the proponents of 50mph
sprint finishes of "Pro races" claim. No one here said that steep
roads straight enough to allow high speeds don't exist.

What do you mean by this absurd disclaimer? Are you making an alibi
for speed embellishment, or what are we to make of it?

Jobst Brandt <jbr...@hpl.hp.com>

Garry Lee <gl...@iol.ie> wrote in article <6797co$bcp$2...@nuacht.iol.ie>...

<stuff deleted>

Please don't say "dead" in this thread.

I have tried Oakville grade, Petrified forest and Geysers but the hill
were I went the fastest was the downhill of Marmolada (Dolomites) which
has the big advantage of being straight and fairly steep for a long
time. The fastest I went was 89 Km/h (55.7 Mph) and believe me I was
trying to pass 90km/h.
Emilio

Jobst Brandt wrote:

No, I was not pedalling and I never said anything about a race. With a
53x12, what good would pedalling do anyway? None.

Unfortunately, noone here has a sense of humor. It was smartass remark
based upon the numerous responses people post wherein only those with
"scientific proof" are given credibility. Do I know if my cyclocomputer
is accurate - NO. But is always with .2 to .5 mph of others I ride with,
so it is accurate enough for me.

> Jobst Brandt <jbr...@hpl.hp.com>

I don't know where you folks ride, but I can hit 50 mph any day of the
week. I will add that is downhill, pumping a 53-13 for all it's worth.
Now, if I were to shed a few grams and add a 12, I'm sure I could hit
55-60 mph. Members of my club do it all the time, on specific downhills
(one is named Asphyxiation Hill, in case you're trying to climb it)
around town. Plus, I don't live near mountains, just good, steep
rolling hills carved eons ago by the Ohio River.

I concur. Why the thinly veiled accusation in response to a little
levity? Take a bong hit, Monsieur Brandt! Man, in a newsgroup filled
with heavies, you're the heaviest, IMHO...

We've got plenty of hills around here where you can get on top of a
53-12 and you won't be anywhere near 55 mph. 40-45mph, maybe, 55mph,
no way.

Jeff

In article <3496169A...@zipcon.net>, Mark Bulgier
<bul...@zipcon.net> wrote:

*** Also Respond via Email to paul-...@att.net ***

Just for everyone's perspective, a Chinook, especially in Boulder, is a VERY
strong wind out of the west. About 18 years ago a Chinook blew a box car off
the tracks up there. In other words, a Chinook tail wind is a real advantage
in setting personal speed records.

Tom Gibb <TBG...@aol.com>

> I don't know where you folks ride, but I can hit 50 mph any day of

It isn't worth much and if you would stop pedaling for a moment on
tuck in, you might reach that higher speed that riders claim they
pedal. Besides, the calim was that professional racers sprint at
these speeds regularly. That is not the case.

This is a common thread among people who believe they can go fast
pedaling down hill. The power required goes as the cube of velocity
and because most people have no feel for things that vary with the
third power, they believe that if they wanted, they could go faster.
Not so.

Yes, that's also an old saw. I know a guy who actually saw someone
do this. Really!

Jobst Brandt <jbr...@hpl.hp.com>

My 1997 USCF rulebook lists the world record in the
flying 200 as 9.865 sec in Bogota, by Curt Harnett.
This works out to a little over 45 mph, and it's not
just chance that the world record was set at altitude.

The differences between a flying 200 and a field sprint
are there is no lead out in a flying 200 and on the
track you get a better riding surface and you get to
dive down off the banking making it a downhill sprint.
Also, Harnett was almost certainly riding a disc wheel,
something to don't see in pack sprints.

I think it's *extremely* uncommon for pros to sprint
at 50 mph. Since downhill finishes are rare you would
need a honkin' tailwind to get up that fast.

Bob Schwartz
bsch...@cray.com

As a flyweight spinner, I have no problems staying smooth in a 50x13
at 45 MPH (about 150 RPM), although doing so is slightly slower than putting
the pedals at 3 and 9 o'clock and tucking my knees in against the top tube.

--
"Come to the edge, Life said. They said: We are afraid. Come to the edge,
Life said. They came. Life pushed them...and they flew." -Guillaume Apollinaire
Work: dr...@Qualcomm.COM Play: dr...@PoohSticks.ORG
Home Page: <a href="http://www.poohsticks.org/drew/">Home Page</a>

50-60MPH are fairly typical Chinook winds, although on ocassion they exceed
100 MPH.

On the nearly flat (ie, I'm 3 MPH faster on my way in than on my ride home)
road leading to my office, I've completely spun out at 150 RPM and 45 MPH.

>Erik (who?) snipes:
more importantly, where does eric ride? i live in louisville, on the ohio...

i know how the hills are around here and know that about 56ish is the highest
speed you can hit. around here. perhaps you live in cincinnati. maybe not.
there is no way you pedal that fast... try coasting.

That's the point. Many contributors to this thread have not tried
this and much less done comparisons descending down a section next to
a rider who is coasting, tucked in. It is amazingly demoralizing to
sit up, pedal like hell and fall behind rapidly as the other guy rolls
away without effort.

The one that makes this most obvious is approaching a city, both
riders realizing that they must do something special to win the
sprint. The one who sits up first to pedal usually loses. The real
way is to know exactly where the sign is and drop in behind the other
guy to take a coasting flyer that comes around just before the sign.

Jobst Brandt <jbr...@hpl.hp.com>

>Just for everyone's perspective, a Chinook, especially in Boulder, is a VERY

>the tracks up there. In other words, a Chinook tail wind is a real advantage

I wonder what kind of speeds a bike could have hit in Guam recently?

--
John P. Serafin | Operating a bicycle is more like driving than riding.
jps at pobox com | Operating an automobile is more like riding than driving.

If you caught the right gust, 236 mph. Two seconds of glory and
kerplunk.

Scott

The most famous video of Kelly descending would be his amazing
run down from the Poggio in the '92 Milan-San Remo. I do not
believe for a second he hit that kind of speed, it's way too
technical a descent.

He won that race with his speed through the switchbacks, not on
the straights.

Bob Schwartz
bsch...@cray.com

>

Employees of the shop sponsoring FFCT regularly hit the high 50s when
riding down Floyds Knobs (Indiana). Try Broad Run Road in far eastern
Jefferson County (Kentucky). I've ridden this route 100 times if I've
ridden it once. Coasting down I hit 44. Pedaling hard as I can, I hit
48-49, which disproves Mr. Brandt's theory. However, Mr. Brandt may be
right that, even with a 53-12, my speed would not increase. Still, my
speed is impacted by pedaling, and I have to wonder if a bigger gear
wouldn't add one or two miles an hour, particularly if I'm drafting.
While that's not much, there's a huge psychological difference between
49 and 51.

I don't see why this proves anything other than that you went 44mph.

How about racing another rider of roughly equal stature down that hill
and see what goes faster, coasting in a good crouch or pedaling.

As I mentioned, coasting at 50mph in pedaling position, a rider could
add about 2mph by pedaling and about 10mph by crouching into a minimum
position. This is best appreciated when competing with other riders
who do likewise. Try it.

Jobst Brandt <jbr...@hpl.hp.com>

I have routinely gone over the 40 mph mark on my mountain bike. I did
just under 50 mph at Seven Springs during the nationals this spring on
some of the gravel service roads on the hills. When I was in the Alps
this summer in Southern Germany, Bergesgaden area, I could have easily
gone over 50 mph if I was better at high speed turns. Unfortunately for
me I am not used to such steep and twisty roads. Steepest grade I saw
there on the road was 21%. Steepest grade I rode down hill off road was
over 30% according to the map I have. going up was a bitch but the trip
down was a blast. My forearms got tired just from working the brakes so
hard for so long.

If I had high pressure slicks on the roads there or even a road bike, 50
mph wouldn't have been a big deal given some of the main roads. For me,
I stuck to the trails and some side roads.

Rob

--
email: |"You can't take life too seriously,
rhor...@mailhost.pd4.ford.com | you don't get out alive." Buggs Bunny

Did the recent wind speeds in Guam break the Mt. Washington record for
highest recorded wind speed? I thought the record was 237 mph, but I may
be mis-remembering...

-Ian

Haven't off-road downhillers routinely gone in the mid-to-high 50's (as
measured by radar) at Mammoth, on mountain bikes with knobbies, etc. ?
I know the section on which they are timed is steeper than a road would
be made, but I figure, hey, they are on MTB's, off-road, with aero but
not the MOST aero positions.

-Ian

"for what it's worth, the record for the highest surface wind speed
ever recorded, which was measured at 231 MPH on Mt. Washington, NH, on
april 12th, 1931, was finally broken by a gust measured on Guam at 236
MPH by Typhoon Paka. Our congratulations go out to the Typhoon. Great
job!!"

--
Stella Hackell ste...@apple.com

The really efficient laborer will be found not to crowd his day with
work, but will saunter to his task surrounded by a wide halo of ease
and leisure. --Henry David Thoreau

Without a doubt. While the '92 descent from the Poggio must surely
qualify as one of the epic human achievements, it's not as fast as this
thread is talking about; I'm just talking about a vid from an earlier
TdF Pyrenees stage, where SK somewhow manages to desperately hang on
with the great climbers going up and then on the descent, breaks away
with one other rider and spins/coasts down at over 60 mph. Sorry, maybe
we should move this over to the racing newsgroup!

Sure it is... the only question is whetehr you pedal or
coast to it.

...

Try just about ANY pass in the interior of BC. Like
Richter, Yellow Lakes, Rogers, Kicking Horse etc.

I've hit over 90 kph on all of these

Tom

John Serafin writes:

That is often mentioned about achieving high speeds on a bicycle but
in my experience, high winds seldom increase top speed because they
are so turbulent that you cannot risk high speeds. My best results
have been with 10 to 15mph tailwinds. This is more reasonable because
coasting speeds are almost directly enhanced by the speed of the
tailwind, something that is not true when on the flat pedaling, as
most riders have discovered.

I rode on two passes that are often mentioned with respect to high
speeds that probably never occurred. Conway Summit on (US HWY395) and
Tioga Pass (CAL HWY120) both have long and straight runs on which high
speeds are reasonably safe, neither road is more than 8% and Conway is
probably not more than 6% grade. I descended Conway with gusts of
more than 60mph that came from angles of up to 20 degrees to the side
primarily from behind. We didn't reach 50mph in spite of letting it
roll freely and using the whole of the 4-1/2 lane wide smooth highway.

On Tioga the gusts were as high as 100mph, none of which seemed to be
from behind regardless of which way we were headed. We had hoped to
climb the pass with wind help, but even here the turbulence made it a
net loss but exciting. There was no way to ride when a gust came. We
jumped off and stood legs spread wide leaning on the bike as a brace
until it went by.

Jobst Brandt <jbr...@hpl.hp.com>

Once on our road Sterling, once on our Fisher Gemini (and the FAT tires
were ON). Both times, rock solid steady... no shimmy. But.... we find that
we get more speed in the tight tucks on steep descents, than we do in
sitting up and cranking. The wind is still the enemy.

==============================================================
Brian Managan - GTGTandems - Rochester NY
New York State's Largest Tandem and Recumbent Dealership
Santana, Ibis, Burley, Rans test rides by appointment

Visit our new Website at: www.gtgtandems.com
(716) 872-6120 (business)
br...@gtgtandems.com

(716) 872-1751 (home)
man...@netacc.net

Gear-To-Go Tandems is the sponsor of:
STTR: Southern Tier Tandem Rally (road) - August 1&2, 1998
F.A.R.T: Fall Allegany Rally for Tandems (off-road) - October 2-4, 1998
========================================================================

--
Jim Quinn

Rick Denney
Take what you want and leave the rest.

I've never had the chance to ride with the wind on a mountain pass, since
I live in the Midwest. That might be fun (or really scary).

--
Reach out your hand if your cup is empty;
if your cup is full, may it be again.

-Robert Hunter

snip

One fine day this fall, I found myself in such a heavy crosswind that
I was blown across the road even with spoked wheels. I had to dig my
cycling shoes into the ground on the side of the road to simply stand
upright. But my bike wouldn't stay on the ground without me sitting on
it. Needless to say, I cut my ride short and turned around after the
wind died down a little.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Eric Lin
squ...@NOSPAMinteraccess.com (edit out NOSPAM)
University of Illinois College of Medicine Class of 2001
http://homepage.interaccess.com/~squint

"Me fail English? That's un-possible!" Ralph Wiggum in the Simpsons

> . . . my wife Karen and I have cracked 65mph twice on
> our tandem(s) descending . . .

My personal high water mark is 58 mph, recorded aboard a Nishiki two-fer on
Rte. 19 in Wales, MA. If I've done better on my (uninstrumented) single, it's
on Rte. 118 to Jeffersonville, VT in the Stowe road race. Both were coasting,
and the latter took advantage of drafting through little clumps of riders.

Although tandems usually swing bigger gears, this has little to do with their
higher terminal velocity. The big dog around here is a purple Santana with a
60/12 and 400+ lbs. The 60t "big cookie" gives it a better launch, topping out
at ~125 rpm or 50 mph. It's hard to spin much faster two-at-a-time, and they
coast to full speed in a tuck. At a tandem's top end, even a crafty single has
trouble slinging all the way past, and you're not out there for long. Pedaling
just slows you quicker and scares the poor stoker.

Where slopes are short, sweet and steep (and speedos seldom see sixty),
Todd Holland

--
p...@visi.net
sean_w...@bc.sympatico.ca wrote in message
<349ACA...@bc.sympatico.ca>...

<snip>

The DeciMach prize (75 mph or .1 x speed of sound) is for level, windless
200m.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Brian McKenzie [ Il faut laisser les autres avoir raison.
History graduate student ] Puisque cela les console de n'avoir
velo enthusiast [ pas autre chose.
__* ]
_ \< _ [ Andre Gide
(*)/'(*) ]
[
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Yes, the record was broken. The old record was 231 mph.
Coincidentally, the man who recorded the old record in 1934 passed away
within a few days of the taifun that hit Guam..

--
Karl Frantz * fra...@eng.pko.dec.com

> Drew Eckhardt writes:
>
> > As a flyweight spinner, I have no problems staying smooth in a 50x13
> > at 45 MPH (about 150 RPM), although doing so is slightly slower than
> > putting the pedals at 3 and 9 o'clock and tucking my knees in
> > against the top tube.
>
> That's the point. Many contributors to this thread have not tried
> this and much less done comparisons descending down a section next to
> a rider who is coasting, tucked in. It is amazingly demoralizing to
> sit up, pedal like hell and fall behind rapidly as the other guy rolls
> away without effort.

I have to believe that under all but unusual circumstances, the fastest
speeds are achieved by "tucking in" and not pedaling during the peak speed
time frame. Pedaling hard at the beginning of a steep stretch (and then
tucking) can serve to help reach a high speed if the steep section isn't
very lengthy.

> The one that makes this most obvious is approaching a city limit sign,
> both riders realizing that they must do something special to win the
> sprint. The guy who sits up first to pedal usually loses. The real
> way is to know exactly where the sigh is and drop in behind the other
> guy to take a flyer that comes around about 30 feet before the sign.
>
> Jobst Brandt <jbr...@hpl.hp.com>

I don't know what "The guy who sits up first to pedal usually loses"
means. If you can pass someone in only 30 feet then you must be doing
slow speed uphill sprints.

If two riders are equally skilled in coasting and are coasting
essentially side-by-side, it is the guy who sits up first and spins
who loses mostly because he was too far from the line and the other
rider takes advantage of his draft even half overlapped. I said you
should pass as in "get ahead" of him about 30 feet from the line, too
late for a counterattack.

Jobst Brandt <jbr...@hpl.hp.com>

Andrew Mein

> 57 mph on the flats of Delaware...behind a semi.
> Whipping around a 53/13.

Wow, you must be some sight at 180 rpm. Are you sure that "adrenaline" wasn't
pumping while watching your _Breaking Away_ video?

T. Holland (who's sure his handmade tires are round and true and OK at the
double nickel)

When you lose the pocket you slow down rapidly.

So, T. Holland, give it a try.

--
============== One of "The People Behind MicroStation" ==============
Bruce Frech Phone: (610) 458-5000
Bentley Systems Fax: (610) 458-1060
690 Pennsylvania Drive
Exton, PA USA 19341-1136 Bruce...@bentley.com
=====================================================================

R

[that riders on flat roads ride behind trucks at 60mph]

I see that most of this is done by computing the cadence required,
which by the way is closer to 192 rpm for 60 mph on a common nominal
700-28 or sew-up tire. What escapes these computations is how one can
get up to speed, sitting-on or otherwise. Unless the truck is either
purposely accelerating slowly to not drop the bicyclist, is hauling an
enormous load on a low-bed (that you can't draft), or is descending a
grade where the bicyclist conveniently was already coasting fast
enough to match the speed of the truck, an imagined task.

I have tried this and have observed others who tried to sit-on a truck
at such speeds and it never worked except at lower speeds. That it
didn't work, did not prevent these riders from deriving that it would
have been possible had they only sprinted a little harder, knowing
that people can spin that fast. Therefore, they say they did it.
What they fail to recognize is that there is practically no net power
from that effort, most of it going to turning the pedals and wheel.
Just try to get a rear wheel up to 60 mph on a stationary bike with a
freely suspended rear wheel.

This falls in the category of John Howard pedaling his land speed
record. He had to be towed to near the record speed because below 100
mph there was insufficient turbulent push behind the wind wall to keep
the bike in contact. Ultimately the throttle was placed on the
bicycle so he could control his position while pedaling, as with all
these efforts, was a sham.

Jobst Brandt <jbr...@hpl.hp.com>

While I can't spin anywhere near that fast, I once saw Dan Henry, when
he was in his _seventies_, pedal on rollers at 200 rpm, as determined by
my stopwatch. And amazingly, he did it with no clips - he said they
scared him!
--

Frank Krygowski ae...@yfn.ysu.edu

Andrew Mein

I havn't done any truck drafting. The closest thing was when I was a kid
we would tuck in behind a London (Leyland) bus and get up to 35MPH or so.
These had bodies that came very low to the ground, so there probably
wasn't much air underneath the bus, this might have helped. There was
also some kind of finishing strip along the bottom edge that was below
wheel centre, I'd guess there was less than 10 inches from there to the
ground. At low speeds we'd ride two abreast behind busses and try to
impress each other with how hard we could push on the bus. The goal was
putting black tyre marks on the bus and/or getting the best squeal out of
the front tyre. We'd also make contact with the bus and try to avoid
using our brakes as the bus came to the next stop - another "chicken"
game. I know, lucky to have lived through it.... and helmets were only
for the track.

I see this as driving a motor vehicle. The fact that he was on a bicyle
that didn't have a direct drive from an engine is a technicallity, he was
"air coupled" to the motor vehicle that was providing most of the power.

> Jobst Brandt <jbr...@hpl.hp.com>

7 miles south of Charlottesville, VA on rt 29 (a smooth 4 lane divided
highway with almost no traffic and no intersections in those 7 miles)
there is a side road where stone trucks regularly pull out and head
north. We frequently used that road to finish our rides.

The last 7 miles started with about a mile of gradual uphill which I
could hold 20 mph when riding real hard. Occasionally a truck would
pull out and I would catch it as it started. So both I and the truck
started slowly. Once I drafted a truck all the way up the hill (at
about 30 mph) and down the other side and another mile on the flats.
The downhill was steeper than the uphill and the truck did not use it's
brakes or engine to control it's speed. With suitable calculations one
could compute it's likely speed (mass, drag, slope, ....) but it was
obvious to me and my cyclocomputer we were well over 50 mph (the max
speed it could display was 50 mph and it was maxed). Once we were over
about 40 mph I didn't pedal to maintain speed. I pedaled just to adjust
position within the pocket. I was adding power, so there was a net
increase in power. When I finally left the pocket I rapidly slowed.
Pedaling then would have little use so I didn't.

The wind from the truck was "turning the wheels" and pulling me along.
My added power had an effect on my speed. F=ma, and when I added force
I accelerated.

This was in 1983. We also regularly rode down a pass that had a 10+%
one kilometer straight section where the computer would max out so I was
familiar with those speeds. I no longer encounter situations (very
heavy trucks starting from stop on smooth roads) to replicate with more
accurate speedometers. Thus this may be classified as lore (except that
others have reported similar events).

-Bruce Frech

> ...

You changed the scenario from that which was under discussion. The
claim was that on level ground they drafted trucks at over 60mph. My
response made that clear and I also pointed out that it would take a
hill to get to such speeds. I don't doubt that one can draft trucks
at such speeds but the stories that pop up here always embellish the
imagined event to a degree that it reeks of BS. Your event appears
more close to reality and doesn't raise the BS flag as the ones so
often presented. I have done much of this stuff and when a poseur
comes along, it doesn't ring true.

It is this effect that gets me into expert witness work defending the
bicycle industry against guys who fell off their bikes and blame
everyone else to protect their egos. I have not yet seen a case with
merit. I have always been able to discover the actual sequence of
events that were nothing like the plaintiffs claim. I've fallen off a
bike most of the ways one can do it, and those that I haven't, I've
seen others do. The BS artists can't imagine that.

Jobst Brandt <jbr...@hpl.hp.com>

Have you ever hit a bouncing football with your chainwheel at 25mph?
I have. Something I will never forget. My friend who was with me says
that I and bike shot up into the air. I can't vouch for that but what I
can say is that it was the worst smash I ever had, even though I broke
nothing. I had 9 significant cuts/abrasions and one on my hip which was
bigger than a dinner plate.

Let's play "who can top that and still tell the truth"

In southern Spain they grow sugar beets for sugar. At harvest time
the trucks that haul them make the perfect pacing partners since they
are so heavily loaded. They can't get past 40mph or so. The hazard
comes when the truck hits a bump and five or ten of these sweet potato
looking tubers come floating out of the back!

I also remember a friend getting up to about 90 kph behind a truck on
flat land. I decided to drop off at 70-75 kph when he started tapping
the mud flaps with his front tire!

George.

While I cannot say that I've ever drafted a truck at 55-60, my own
experience leads me to believe it's entirely possible. I have drafted a
truck at 45-50 mph and found that the push I received from behind was
strong enough that I was actually using the brakes as much as I was
pedalling, in order to avoid colliding with the rear bumper. I've also
found that rideing behind the wheels - rather than in the center of the
truck - provides a better draft.

At the risk of raising Jobst's BS detector, I have to tell you the rest
of the story. It was in 1979, back when I was racing. One of my training
partners and I did a lot of truck-drafting (2-3 times/week) and I was
used to jumping on any available draft. I caught a loaded sand and
gravel truck and ensconced myself behind the left side wheels for the
next 14 miles (the longest draft I've ever had, usually they were no
more than a mile or two and often much less).

On a section of four-lane road the truck pulled into the left lane and I
followed him over. Shortly thereafter, we passed a guy in the right lane
in a maroon Pinto. I wanted to wave, but the best I could do was shoot
him a quick smile and wiggle a couple of fingers. You should have seen
the look on his face!

There is a famous case in Scotland where the policecar video caught a chap
draughting an oil tanker on the way into Inverness - he was reportedly doing
70 mph. (it's a long steep hill - dual carraigeway) - The guy was doing a
Lands End to John 'O Groats charity ride.

He didn't get booked - presumably because the policemen dined out on this
story for years afterwards...

callum

-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Callum Wilson Mountain Biker, Internet Consultant
Import java.awt.disclaimer;
Logica UK Ltd. http://www.logica.com
Rapid Descent Innovations. http://www.proflex.demon.co.uk

The policeman wandered up to him and wearily asked him, as Cockneys
characteristically do when being funny

"havin a little trable tyking orff den, Sir?"