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Bumps and efficiency



 
 
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  #1  
Old June 29th 06, 08:02 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

Do bumpy road surfaces typically exact costs in riding efficiency?
While doing a loop that I've ridden dozens of times, I noticed that my
speed had dropped almost two MPH from my norm on a section that had
recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked (at
least, no more than usual), there didn't seem to be any wind, and I was
able to ramp the speed back up to normal after turning off the choppy
surface, all of which led me to question whether it was indeed the
bumpiness that was affecting me.

Does anyone have any similar anecdotes? Any studies of this? Was I
dreaming? I'm curious if it is more beneficial in a long ride/race
where crappy roads are the norm to use 25mm tires vs. 23s.

TIA,

SYJ

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  #2  
Old June 29th 06, 08:17 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

Yes, most definitely. For the same reason that knobby tires are less
efficient than smooth ones (on pavement, anyways).

On a bumpy road, part of your energy output is used to overcome the
bumps, leain less for propelling you forwards. Therefore you have to put
out more energy to accomplish the same amount of horizontal movement.

- -
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"Your Friendly Neighborhood Wheelman"

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

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

  #3  
Old June 29th 06, 08:20 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

On 29 Jun 2006 12:02:23 -0700, "SYJ" wrote:

Do bumpy road surfaces typically exact costs in riding efficiency?
While doing a loop that I've ridden dozens of times, I noticed that my
speed had dropped almost two MPH from my norm on a section that had
recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked (at
least, no more than usual), there didn't seem to be any wind, and I was
able to ramp the speed back up to normal after turning off the choppy
surface, all of which led me to question whether it was indeed the
bumpiness that was affecting me.

Does anyone have any similar anecdotes? Any studies of this? Was I
dreaming? I'm curious if it is more beneficial in a long ride/race
where crappy roads are the norm to use 25mm tires vs. 23s.

TIA,

SYJ


Dear SYJ,

Yes, rougher surfaces slow tires down.

Coefficient of Rolling Resistance
Wooden Track 0.001
Smooth Concrete 0.002
Asphalt Road 0.004
Rough but Paved Road 0.008

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

If you plug those values into the calculator and use the defaults, you
get speeds of 7.79, 7.68, 7.46, and 7.04 m/s, or 17.43, 17.18, 16.69,
and 15.75 mph.

The effect of chip seal is quite noticeable. My daily downhill speed
improved nicely years ago after the wretched chip seal was paved.

Cheers,

Carl Fogel
  #4  
Old June 29th 06, 08:22 PM posted to rec.bicycles.tech
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Default Bumps and efficiencyP.S.

If you regularly ride a good portion of chip & tar (or as I like to call
it "40 grit") pavement I would seriously consider tires no less than
25mm wide.

Here in the Carolina Piedmont, where most secondary roads are of this
type, you almost never see anything narrower than 25mm, even on the top
level road racing machines.

- -
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

  #5  
Old June 29th 06, 08:44 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

On 29 Jun 2006 12:02:23 -0700, "SYJ" wrote:

Do bumpy road surfaces typically exact costs in riding efficiency?


Yes, particularly if the bike has high-pressure tires and lacks
suspension.

While doing a loop that I've ridden dozens of times, I noticed that my
speed had dropped almost two MPH from my norm on a section that had
recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked (at
least, no more than usual), there didn't seem to be any wind, and I was
able to ramp the speed back up to normal after turning off the choppy
surface, all of which led me to question whether it was indeed the
bumpiness that was affecting me.


It was the road. There may have been an additional penalty from the
stickiness of the surface if the sealer was leaking through to the top
of the gravel layer, but a good tar-and-gravel application won't put
any tar on the top.

Does anyone have any similar anecdotes? Any studies of this? Was I
dreaming? I'm curious if it is more beneficial in a long ride/race
where crappy roads are the norm to use 25mm tires vs. 23s.


2mm of tire won't help IMO. 15mm might, but I would expect the gain
to be small if any. I can't offer any figures to support that
assertion; it's just an opinion based on limited experience. I know
that swapping from a knobby to a smooth tire of the same size had a
benefit similar to what you saw in the case of the smooth vs
gravel-encrusted surface. Wider tires may produce increased rolling
resistance relative to a narrower one (partially due to running at a
lower pressure), and they add to the frontal profile (and thereby to
drag) somewhat as well.
--
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  #7  
Old June 29th 06, 09:12 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

SYJ wrote:

Do bumpy road surfaces typically exact costs in riding efficiency?
While doing a loop that I've ridden dozens of times, I noticed that my
speed had dropped almost two MPH from my norm on a section that had
recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked (at
least, no more than usual), there didn't seem to be any wind, and I was
able to ramp the speed back up to normal after turning off the choppy
surface, all of which led me to question whether it was indeed the
bumpiness that was affecting me.

Does anyone have any similar anecdotes?


Yes. Around here road maintenance is by county. At many places one can
cross a county line and go from chip seal to smooth pavement or
vice-versa.

Transitioning to smooth pavement is more than enough to shift up a gear,
despite no change in grade or wind direction.

Mark

  #9  
Old June 29th 06, 10:01 PM posted to rec.bicycles.tech
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Default Bumps and efficiencyP.S.


Chris Z The Wheelman wrote:

---snip---
If you regularly ride a good portion of chip & tar (or as I like to call
it "40 grit") pavement I would seriously consider tires no less than
25mm wide.

---/snip---

Is this due to the perception of increased comfort, or because there is
an increase in efficiency (decrease in rolling resistance) due to the
fatter tires?

SYJ

  #10  
Old June 29th 06, 10:38 PM posted to rec.bicycles.tech
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Default Bumps and efficiency

Mark Logan writes:

Do bumpy road surfaces typically exact costs in riding efficiency?
While doing a loop that I've ridden dozens of times, I noticed that
my speed had dropped almost two MPH from my norm on a section that
had recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked
(at least, no more than usual), there didn't seem to be any wind,
and I was able to ramp the speed back up to normal after turning
off the choppy surface, all of which led me to question whether it
was indeed the bumpiness that was affecting me.


Does anyone have any similar anecdotes? Any studies of this? Was
I dreaming? I'm curious if it is more beneficial in a long
ride/race where crappy roads are the norm to use 25mm tires
vs. 23s.


As everyone else has said, yes, bumpy roads make you go slower. The
book "Bicycling Science" (Wilson, MIT Press) cites a study that
looked at the relationship of energy loss to bump frequency
(i.e. speed divided by peak-to-peak distance of the bumps). One
interesting finding of the study was that energy loss was
proportional to the level of discomfort reported by the rider. So
the more it hurts, the more its slowing you down.


I think this subject got off on the wrong foot, the term "bumps" and
road surface being ill defined. Chip-seal is surface roughness that
flexes tire tread and causes rubber losses. A bumpy road with smooth
surface makes pedaling and sitting difficult. Both have an effect on
speed.

Effect of chip seal is easily seen if one rider coasts down the
shoulder of the road that wasn't chip-sealed while another coasts on
the rough surface. Switching back and forth shows a noticeable
relative difference in speed. As for bumpy roads with, for instance
many smooth patches and dips and lumps, is harder to find for such a
test, such roads generally not being straight enough and constant in
slope to do a coasting test.

I don't believe a chip-seal can take off 2mph through rubber losses
but it can be uncomfortable enough to slow a rider that much together
with the rolling resistance.

Jobst Brandt
 




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