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From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 55-60mph Realistic? Re: High-speed shimmy problem
Date: 17 Dec 1997 16:42:02 GMT

Tom Wertz writes:

> 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.

To which Dave Blake writes:

> 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
> 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.

> In fact, you could take Marty Nothstein in a sprint easily.
> 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      <jbrandt@hpl.hp.com>



From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Max speed with high winds?
Date: 20 Dec 1997 00:38:06 GMT

John Serafin writes:

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

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      <jbrandt@hpl.hp.com>




From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wheel shake
Date: 23 Sep 1998 23:49:37 GMT

Dave Blake writes:

>> You can't "fix it".  You can alter the excitation speed, but it
>> will still be there.

> I don't believe it. Any system with adequate damping will not
> shimmy.  Try to get a bike with knobby tires to shimmy. I have not
> experienced the phenomena on 2.0" tires at all.

You must furnish the reasonable conditions for the above statement,
like, a light weight road bike.  It is obvious that shimmy can be
countered but beyond a certain level, the effort, cost, or weight
makes further pursuit of the matter useless.

> You could also place clamps to tie together different sections of
> the down and seat tube which would at least double the necessary
> speed, and make it irrelevant.

I don't think you will get many takers for a bicycle with extra tubes
that increase the weight of the bicycle, considering that for many
years able bodied racers have been riding frames that can shimmy
without complaint.  I for one have no problem with the shimmy that my
bicycle has above 22mph, because it does this only on smooth roads
while riding no-hands in the resting upright position.  In contrast I
achieve all my maximum speeds, coasting no-hands with hands on the
stem tucked in, knees against the top tube.  This is the most stable
condition for a bicycle and it only gets better as speed increases.
I've been doing this for many years with my riding pals, reaching
unmentionable speeds.  Unmentionable because I don't want anyone else
to feel obligated to emulate them.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: Top speed, was Re: Shimmy - SOLUTIONS?
Newsgroups: rec.bicycles.tech
Date: Sat, 10 Nov 2001 20:16:49 GMT

Matt O'Toole <matt@deltanet.com> writes:

>> The pro's don't go 65MPH unless you want to believe Phil Ligget,
>> who fills his reporting with such tidbits.  Pro's are generally not
>> a heavy as the readers of this newsgroup and the locals don't coast
>> over 50 MPH but rarely, when they have a tailwind downhill or there
>> is a steep straight run on a mountain highway.

> I have no idea how fast they can go in Alpine races, but I've never
> been able to punch through the air at more than 50mph or so on a
> bike.  I don't have a speedometer on my bike, but comparing my
> "terminal" speed to traffic on roads I drive often, I find my top
> speed is around 50mph.  I can't imagine a road steep enough, for a
> long enough stretch, to achieve 65mph.

> I hear they approach 70 mph in the Alps, but I don't believe it.

Don't!

There are few mountain roads in the Alps that are both straight and
steep enough to do this even theoretically.  I weigh more than most
professional racers and ride in the Alps a lot.  I am not guessing
about this and like to descend fast.  Bob Roll told us that on one
stage of the Tour de Suisse, he exceeded 60 MPH for the first time and
was not thrilled by the event because it was early in the stage that
started on a downhill... many bicycles close together.

Jobst Brandt    <jobst.brandt@stanfordalumni.org>



From: jobst.brandt@stanfordalumni.org
Subject: Re: Hit 60mph in less than 3 tenths of a mile.
Newsgroups: rec.bicycles.tech
Message-ID: <Eaj0d.13017$54.182500@typhoon.sonic.net>
Date: Fri, 10 Sep 2004 14:50:12 GMT

Carl Fogel writes:

> Coasting, my money's still on Chalo. This calculator even handles
> tandems, with a note about details

http://www.kreuzotter.de/english/espeed.htm

> Let's roll you all down a long 10% grade, no watts, no
> cadence.

Well I find the calculator does not reflect my experience.  It
calculates a speed of 63.3mph for a 10% grade (no pedaling) and one of
72.6 for 13%.  Whenever I get the opportunity to reach max speed on a
descent, I have taken a run at it and then tucked in, hands on stem
and in practical fetal posture of the upper body and found that I take
at least 13% grade to reach 62mph.  Only with tailwinds have I
exceeded 60mph on 10% grades.  Therefore, I find this calculator not
useful for estimating terminal velocity.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: Hit 60mph in less than 3 tenths of a mile.
Newsgroups: rec.bicycles.tech
Message-ID: <bWo0d.13092$54.183197@typhoon.sonic.net>
Date: Fri, 10 Sep 2004 21:22:15 GMT

Carl Fogel writes:

>>> Coasting, my money's still on Chalo. This calculator even handles
>>> tandems, with a note about details

>> http://www.kreuzotter.de/english/espeed.htm

>>> Let's roll you all down a long 10% grade, no watts, no cadence.

>> Well I find the calculator does not reflect my experience.  It
>> calculates a speed of 63.3mph for a 10% grade (no pedaling) and one
>> of 72.6 for 13%.  Whenever I get the opportunity to reach max speed
>> on a descent, I have taken a run at it and then tucked in, hands on
>> stem and in practical fetal posture of the upper body and found
>> that I take at least 13% grade to reach 62mph.  Only with tailwinds
>> have I exceeded 60mph on 10% grades.  Therefore, I find this
>> calculator not useful for estimating terminal velocity.

> The calculator may well be imperfect, but check me on my guesses for
> you and your bicycle here. (And take a moment to re-check your
> entries--the confounded thing has a nasty habit of silently changing
> defaults on you in a helpful but maddening fashion.)

> I'll put in triathlon (better than hands on drops, not as good as
> superman) for your tuck position, then 72 inches, 180 lbs for rider,
> and 20 lbs for bike (obviously guesses), 5000 feet (maybe high,
> maybe low?), -10 for slope, 0 cadence, 0 watts:

> http://www.kreuzotter.de/english/espeed.htm

> I get 58.9 mph for 10% and 67.6 for 13%, so we're obviously using
> different values.

> The analytic cycling calculator doesn't include pedal motion and you
> have to figure out your own drag notions:

> http://www.analyticcycling.com/ForcesSpeed_Page.html

> For 200 lb = 91 kg, 1.056 for density at 1500 meters, -0.10 slope,
> and default drag inputs of 0.5/0.5, this calculator predicts 23.13
> meters per second, or 51.7 mph.

> But your tuck is presumably better than the defaults, which probably
> assume a pedalling hands-on-drops situation. If we try 0.4 and 0.4
> for the drag inputs, we get 28.91 mps, or 64.66 mph on the 10%
> slope.

> I suspect that riders often overestimate the effectiveness of their
> tucks. They hunch over and pull their arms in, but they were already
> hunched down quite a bit and their arms weren't sticking out much to
> start with.

I estimate the effectiveness of my position on results of casting
side-by-side with other riders and generally being faster as well as
catching and passing riders who believe in pedaling at speeds over
30mph down long grades.

> They often overlook the huge drag reduction produced when they stop
> pedalling at high bicycling speeds.

I don't pedal on such slopes where high speeds are attainable.
Besides, I couldn't pedal when tucked in because my elbows are where
the knees need to be at the top of each stroke... in my gut.

> About all that they do for their legs, cranks, and pedals, which are
> a bigger problem than their arms and upper body, is to put their
> feet at 3 and 9 o'clock and to place the soles of the shoes on the
> crank arms, with one heel and one toe near the bottom
> bracket--something that riders who use clipless pedals rarely do.

Arms and upper body make a significant difference.  I regularly see
riders tuck in with their head and shoulders lower than their butt
that sticks way up.

> If you'll give me height, weights, and elevation, I'll fool
> around with drag a bit and let you know what the calculators
> suggest.

You have them correctly except height 77in body weight 175lbs.

Jobst Brandt
jobst.brandt@stanfordalumni.org


From: jobst.brandt@stanfordalumni.org
Subject: Re: Hit 60mph in less than 3 tenths of a mile.
Newsgroups: rec.bicycles.tech
Message-ID: <Tpq0d.13097$54.183329@typhoon.sonic.net>
Date: Fri, 10 Sep 2004 23:04:19 GMT

Carl Fogel writes:

> For a beanpole 175 lb rider 77 inches tall in a triathlon tuck on a
> 20 lb bike at 5000 foot elevation, 10% grade, 0 watts and 0 cadence,
> and defaults elsewhere, this calculator:

http://www.kreuzotter.de/english/espeed.htm

> predicts 58.0 mph. Tilt things to 13% and it expects 66.5 mph. Your
> tuck might not be as good as a triathlon bike configuration in
> normal pedalling, but the lack of pedal motion while coasting could
> make up for that.

Well... as I said that's too high a speed.

> These seem like fairly good predictions.

Not to me, considering that there are few places in all the mountain
roads I have ridden in California and in the Alps where 60mph was
reached.  In fact the most commonly touted run is Tioga Pass CA, east
slope for 60mph.  It may be at 9000ft but it doesn't go any 60mph
without a wind AND an assist from a camper truck past which one can
take a flyer.  Otherwise a bit over 50mph is possible.

I must qualify that by assuring you that my tuck position, knees
together under top tube, hands on stem, elbows in gut and back
horizontal, is faster than any rider's with whom I have ridden except
one who weighed over 250 and who used a similar position.  That he was
faster was tested on the long straight run of HWY395, Conway Summit
Pass going north at the red cursor on this map:

http://www.topozone.com/map.asp?z=11&n=4223454&e=308561&s=100&size

> Let's try the other calculator:

http://www.analyticcycling.com/ForcesSpeed_Page.html

> For 175 lb rider and 20 lb bike at 88.6kg, 1.056 for the air density
> at 1500 meters, -0.10 slope, and 0 watts for coasting, with 0.5/0.5
> drag figures and the usual 0.004 rolling resistance coefficient for
> an asphalt road, Tom Compton's calculators predicts 23.33 meters per
> second, or about 52 mph.

That's a bit closer but you must realize by now that these speeds
compare as their squared values because that is the air drag effect.
Thus they are farther apart than the speeds at first appear.  I don't
believe this is a good method for indicating how fast a rider will
coast down a hill, there being too large a spread in results among
programs that should be applying the same values.  The math is simple.
It's the constants that are difficult to guess.

> Reduce the frontal area and drag coefficient by the same arbitrary
> 20% used in the last post to 0.4/0.4 and the result is 29.16 mps, or
> around 65 mph.

That's a large change in area.

> The wider range is likely due to the difference between the
> kreuzotter's better informed decision about what drag is for a
> triathlon setup than my purely arbitrary switch to 0.4/0.4.

> Another approach would be to compare the kreuzotter hands on the
> drops results with its triathlon results on the assumption that your
> tuck lies somewhere in between. With the triathlon setup, the
> 77-inch 175 lb rider on a 20 lb bike at 5000 feet coasted down the
> 10% grade at 58.0 mph.

> On the drops, he rolls only 52.9 mph.

Well, I roll right by people with hands on the drops with about 5mph
or more at 50mph.

> So presumably your tuck is somewhere between the 52.9 mph on the
> drops to 58.0 on a triathlon.

I find the whole method questionable.  Again, its for lack of an
adequately accurate model on which to apply the equations.

> Since your earlier post indicated that your experience was often
> lower speeds than predicted, another factor is the length of the
> run. Accelerating those last few miles per hour takes much longer
> than the initial 90% of the drag race. Here's a calculator for
> graphing terminal velocity:

Not to worry, I am aware of that and make sure that the run is long
enough to yield insignificant additional increases.  My 0.1 resolution
Cyclometer is steady and records the maximum.

Note: "triathlon"

Jobst Brandt
jobst.brandt@stanfordalumni.org

 






































































































































































































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