Sustaining higher speed

yk said:

Assuming no acceleration, flat road, no wind, does it require more effort
to sustain higher speed ?
If yes, what would be the incremental force needed ?
Apparently, it does not require x2 force to sustain x2 speed. Correct ?
I presume, the air resistance plays an important role.
Could somebody explain ?
Thanks.

Neglecting the small difference in rolling resistance the power required

varies as the cube of the speed. This means that to go twice as fast
requires eight times the power.

HTH,
Ernie

someone said:

Assuming no acceleration, flat road, no wind, does it require more
effort to sustain higher speed? If yes, what would be the
incremental force needed? Apparently, it does not require x2 force
to sustain x2 speed. Correct? I presume, the air resistance plays
an important role. Could somebody explain?

I think you mean power not force but that effect, air resistance being
the effort, is contained in the folloing:

http://www.sheldonbrown.com/brandt/wind.html

[email hidden]

yk said:

Assuming no acceleration, flat road, no wind, does it require more effort
to sustain higher speed ?
If yes, what would be the incremental force needed ?
Apparently, it does not require x2 force to sustain x2 speed. Correct ?
I presume, the air resistance plays an important role.
Could somebody explain ?

Power required increases with the cube of speed. So doing 40mph
requires 1.6kW if 20mph requires 200W. That's why you can't ride at
40mph for more than a few seconds, if at all.

On Tue, 22 Mar 2005 18:41:50 +0000, Zog The Undeniable

may have said:

yk said:

Assuming no acceleration, flat road, no wind, does it require more effort
to sustain higher speed ?

Power required increases with the cube of speed. So doing 40mph
requires 1.6kW if 20mph requires 200W. That's why you can't ride at
40mph for more than a few seconds, if at all.

Except downhill and/or with a stiff tailwind, but the OP wasn't asking
about that...

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On Tue, 22 Mar 2005 14:28:02 -0700, [email hidden] may have

Quoted message said:

.... if we roll a 6'5" 185-lb Brandt
on a 20-lb bicycle down an endless 7% grade with no wind and
his hands on the drops at 5,000 feet, what terminal velocity
do you predict and why?

If his hands are on the drops at 5000 ft, where's the rest of him if
this grade is in the San Jose area? Wouldn't that be an awfully tall
bike?

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Werehatrack said:

If his hands are on the drops at 5000 ft, where's the rest of him if
this grade is in the San Jose area? Wouldn't that be an awfully tall
bike?

From the pictures I've seen, Jobst does ride an awfully tall bike:

http://www.sheldonbrown.com/brandt/

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Thank you all. Very interesting. and educational.
Since the wind resistance is a dominant force at higher speed, it seems to
make more sense to spend money for a device such as an aerobar than a carbon
bottle cage ;-)
Is there any other ideas or products that helps reducing wind resistance ?
I've seen acryl canopy(?) for a recumbent. Is there such device for a
regular road bicycle ?

On Tue, 22 Mar 2005 19:25:38 -0800, "yk" <[email hidden]> may have

Quoted message said:

Thank you all. Very interesting. and educational.
Since the wind resistance is a dominant force at higher speed, it seems to
make more sense to spend money for a device such as an aerobar than a carbon
bottle cage ;-)
Is there any other ideas or products that helps reducing wind resistance ?

Many things are marketed. Their value is often questionable. The
rider accounts for the bulk of the frontal area, so that's the logical
place to seek efficiencies, though it's also the most difficult to
objectively measure without a wind tunnel.

Quoted message said:

I've seen acryl canopy(?) for a recumbent. Is there such device for a
regular road bicycle ?

It's been tried. The problem is that in any environment where there
is a crosswind, such a fairing can act like a sail, making maintenance
of vertical stability a bit of a challenge. It also tends to add
significant weight and reduce ventilation for the rider...which, in
turn, can lead to overheating and the attendant problems.

To go faster, first build strength and endurance, then work on riding
technique; when you approach the level of performance of the dedicated
athlete, it may be time to worry about modifications to the bike
itself. Until then, the bike is not the important limiting factor.

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Quoted message said:

Carl Fogel writes:

Quoted message said:

Quoted message said:

Er, I think you mean why do I believe these three different
calculators?

Quoted message said:

Probably because I believe that the three different programmers
spent considerable time on the subject and looked at how to predict
power and speed for a variety of bicycles rolling on a road. They
also seem to predict coasting speeds on my daily ride fairly well,
given weight, tuck, and slope.

I suspect they all used a similar model and that the faster you go the
less mechanical losses are involved in the result. How much that is
is unclear because the equipment is not specified.

The three sites agreed that a cyclist on the drops of a regular upright
bicycle would have about 6.8 times the energy expenditure at 40 mph as
compared to 20 mph. Since we also know that energy to overcome air
resistance goes as the cube of speed and energy to overcome rolling
resistance and frictional losses goes linearly with speed (constant drag
force) we can determine the relative contributions of air resistance vs.
the other losses. The results are consistent if at 20 mph about 20% of
the energy is used to overcome rolling resistance and frictional losses
and 80% is used to overcome air resistance. When we get to 40 mph just
over 94% of the energy is used to overcome air resistance.

Quoted message said:

I prefer to
separate the variables and look at wind losses independently of
mechanical losses. That way people will not draw incorrect
conclusions from an undefined model.

That's fine as long as relevant parameters are not left out. In this
case it seems reasonable to include the effects of factors other than
air resistance even though that's by far the largest contributor to drag.

On Tue, 22 Mar 2005 20:14:33 -0800, Peter <[email hidden]> may

have said:

Quoted message said:

I prefer to
separate the variables and look at wind losses independently of
mechanical losses. That way people will not draw incorrect
conclusions from an undefined model.

That's fine as long as relevant parameters are not left out. In this
case it seems reasonable to include the effects of factors other than
air resistance even though that's by far the largest contributor to drag.

I would point out that all such generalized calculators must, as a
matter of course, make some assumptions about the magnitude of various
contributuions to the total energy requirement. As such, unless the
numbers happen to be dead on for a specific instance, they're really
only useful for estimation of relative effects, not determination or
prediction of specific results applicable to a particular rider. As a
tool for illustrating the *potential* (lack of) magnitude of the
change in performance of a rider due to a given tweak, and little
more. In reality, the bike/rider system is sufficiently complex, and
the factors that effect a given rider's instantaneous speed are so
many (and not limited to what's listed, by any means), that such
estimates are unlikely to reflect actual results unless considerable
attention is paid to accurate measurement of each of the components of
the total...and that's a decidedly nontrivial task.

Such tools can be useful for certain purposes, but predicting the
actual speed a rider will attain is probably beyond them for reasons
that have nothing to do with the accuracy of their algorithm.

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yk said:

Thank you all. Very interesting. and educational.
Since the wind resistance is a dominant force at higher speed, it seems to
make more sense to spend money for a device such as an aerobar than a carbon
bottle cage ;-)
Is there any other ideas or products that helps reducing wind resistance ?
I've seen acryl canopy(?) for a recumbent. Is there such device for a
regular road bicycle ?

Yes. See <http://www.zzipper.com/prod_upright.htm>. These fairings are
polycarbonate not PMMA (acrylic), since PMMA is brittle at normal
temperatures while polycarbonate is generally not brittle above about -60C.

A few full fairings have been tried on uprights, but due to the huge
side area, these can only be ridden in very low winds. A lowracer
recumbent is a much better platform for a full fairing e.g.
<http://home.arcor.de/zoxed/photos/images/bikes/velomobiles/john_tetz_foam_fairing_l.jpg>.

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

Carl Fogel said:

...
Instead of increasing by a factor of 8 when speed doubles,
the power seems to go up by a factor of around 6.5. Or so
the folks who worry enough about it to calculate it predict.
Probably the transmission and rolling resistance fail to
increase wildly with speed--unlike wind drag.

I was going to ask if this was for air or milk filled tires, but then I
figured that someone would have a cow if I continued to milk the curdled
joke long after it should have been put out to pasture.

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

On Wed, 23 Mar 2005 00:05:18 -0600, Tom Sherman

may have said:

Carl Fogel said:

...
Instead of increasing by a factor of 8 when speed doubles,
the power seems to go up by a factor of around 6.5. Or so
the folks who worry enough about it to calculate it predict.
Probably the transmission and rolling resistance fail to
increase wildly with speed--unlike wind drag.

I was going to ask if this was for air or milk filled tires, but then I
figured that someone would have a cow if I continued to milk the curdled
joke long after it should have been put out to pasture.

Cheese, guy, can't you do any butter than that?

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On Tue, 22 Mar 2005 21:29:11 -0700, [email hidden] may have

Quoted message said:

With a 195-lb rider and 20-lb bike at 1000 feet, a 0.38 cda
suggested for a racing-position diamond-frame bike, and a
0.0075 crr for touring tires (there's a table below the
calculator) . . .

20.0 mph 245 watts
40.0 mph 1575 watts (6.43 x 245)

A 'bent with a rider of that weight at an altitude of 1000 ft around
here would probably reach a speed of about 70mph just before impact.

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On Tue, 22 Mar 2005 21:29:11 -0700, [email hidden] may have

Quoted message said:

With a 195-lb rider and 20-lb bike at 1000 feet, a 0.38 cda
suggested for a racing-position diamond-frame bike, and a
0.0075 crr for touring tires (there's a table below the
calculator) . . .

20.0 mph 245 watts
40.0 mph 1575 watts (6.43 x 245)

Correction: A 'bent with a rider of that weight at an altitude of
1000 ft around here would probably reach a speed of about 120mph just
before impact, assuming that the system has approximately the same
coefficient of drag as the rider would alone. (Forgot a conversion of
units there on the first pass.)

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Werehatrack said:

Not even close; the incremental increase ratio is closer to the ratio
of the difference of the squares, so doubling the speed could require
approximately four times the force, which is eight times as much
energy.

Not to be pedantic, but it's power, not energy.

Werehatrack said:

I would point out that all such generalized calculators must, as a
matter of course, make some assumptions about the magnitude of

various

Quoted message said:

contributuions to the total energy requirement. As such, unless the
numbers happen to be dead on for a specific instance, they're really
only useful for estimation of relative effects, not determination or
prediction of specific results applicable to a particular rider. As

a

Quoted message said:

tool for illustrating the *potential* (lack of) magnitude of the
change in performance of a rider due to a given tweak, and little
more. In reality, the bike/rider system is sufficiently complex, and
the factors that effect a given rider's instantaneous speed are so
many (and not limited to what's listed, by any means), that such
estimates are unlikely to reflect actual results unless considerable
attention is paid to accurate measurement of each of the components

of

Quoted message said:

the total...and that's a decidedly nontrivial task.

Such tools can be useful for certain purposes, but predicting the
actual speed a rider will attain is probably beyond them for reasons
that have nothing to do with the accuracy of their algorithm.

I think you missed your calling, you could make a good living writing
indeciperable disclaimers.

Werehatrack said:

On Wed, 23 Mar 2005 00:05:18 -0600, Tom Sherman

may have said:

Carl Fogel said:

...
Instead of increasing by a factor of 8 when speed doubles,
the power seems to go up by a factor of around 6.5. Or so
the folks who worry enough about it to calculate it predict.
Probably the transmission and rolling resistance fail to
increase wildly with speed--unlike wind drag.

I was going to ask if this was for air or milk filled tires, but then I
figured that someone would have a cow if I continued to milk the curdled
joke long after it should have been put out to pasture.

Cheese, guy, can't you do any butter than that?

Udder nonsense. It makes me wanna s-cream "bull" .

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

On 23 Mar 2005 04:53:38 -0800, "Peter Cole" <[email hidden]>

may have said:

I think you missed your calling, you could make a good living writing
indeciperable disclaimers.

BTDT, actually, but I'm out of practice.

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