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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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.

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SYJ said:

Do bumpy road surfaces typically exact costs in riding efficiency?

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

Quoted message said:

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.

Quoted message said:

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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On Thu, 29 Jun 2006 15:22:11 -0400, [email hidden]

(Chris Z The Wheelman) said:

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.

Here in sunny, parched[1] Houston, there is an additional reason to
favor tires of greater width, with my preference being not to drop
below 30mm; we have *lots* of wide, open linear seams in our streets,
and wider tires traverse these much more safely and predictably than
narrow ones. (The presence of lots of small potholes and heaves also
mitigates in favor of the wider tires, due to their greater ability to
go over such obstructions without pinch-flatting.)

I have one roadie with 25mm tires; I have to exercise much greater
caution when riding it than with any of the other bikes in the stable.

[1] It's not raining at the moment.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

SYJ said:

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

SYJ said:

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.

I have definitely noticed an effect going across bumpy bridges on the
bike trail. Even though I slow down, I have a few seconds of fatigue
after going across the bridge. I think there may be an interaction with
the shock directly causing muscle fatigue. It reminded me of the
athletic wear that is supposed to decrease fatigue by providing
stabilization of the muscles. I don't know, but I think there may be
something to it.

This may be different from what you are describing because you said you
didn't feel cooked, but the effect may have been more subtle for you.
These bridges will bounce your water bottle out if the holder isn't
snug.

On Thu, 29 Jun 2006 15:22:11 -0400, [email hidden]

(Chris Z The Wheelman) said:

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.

Assuming we're talking about same model of tyre, same tyre pressure,
how would that be any better than decreasing the 23mm tyre pressure a
bit - say, from 120 to 110 psi, for instance??

cheers,
jbr

Chris Z The Wheelman wrote:

---snip---

Quoted message said:

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

SYJ said:

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 🙂

-Mark

Mark Logan said:

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

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

SYJ said:

Do bumpy road surfaces typically exact costs in riding efficiency?

Yes... but it is difficult to tell how much.

I've seen no testing that addresses this, but Bicycling Science
discusses it briefly. They show an old chart developed by the army (for
tank crew) that gives power absorbed by a person's body versus
frequency and amplitude. An amplitude of only .1 inches corresponds to
~50W power loss at 5hz (10.7m/sec; 23.9mph... if the bump occurs once
per wheel rev). Some approximate values from the chart are tubulated
below:

Amplitude (inches), Frequency (hz), Speed (mph), Power Absorbed (W)

..1, 4, 19.0, 3
..1, 5, 23.9, 50
..1, 6, 28.6, 100

..25, 4, 19.0, 290
..25, 5, 23.9, 1200
..25, 6, 28.6, 1900

Clearly, the losses go up a lot with increasing frequency and
amplitude. In a field test this would tend to mimic aero losses more
than rolling resistance. In fact it would increase much faster with
speed than even the aero losses.

The difficult thing is relating this to a bicycle. I don't think I
typically ride on any roads that are smoother than .1 inches every
wheel revolution... so am I lossing 50-100W when riding at a good
speed? Somehow I doubt it. Probably, considerable attenuation of
vibration occurs before it reaches the rider's body. I would expect
elastic parts like tires, stems, frames, seats, etc, to absorb little
energy (ie they would flex with little loss). Still, .1 inches is not a
lot of motion, and I'm sure I experience that much fairly often... on
my hands and butt.

If someone wanted to test for this, a large roller with a rough surface
could be constructed, and the tire could be weighted by an actual
person... ie have a bicycle with rider on top supplying the force. Or
maybe someone with a good power meter could do a field test on
different surfaces.

Quoted message said:

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.

I'd think so... even 28s... and drop the pressure as low as you dare. A
good quality tire suffers little degradation in Crr going from
120-80psi even on an extremely smooth surface, so I think you'd be
faster... and that doesn't even consider the comfort issue!

Quoted message said:

of discomfort reported by the rider. So the more it hurts, the more
its slowing you down 🙂

.... which is probably as good a gauge as any. If the vibration is
enough to be noticable and annoying, you could go faster (as well as
more comfortably!) by lowering the pressure.

Quoted message said:

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.

Do you know the approximate speed and difference in speed when you
experienced this?

SYJ said:

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.

It's more a matter of the vibration affecting the engine than any increase in
rolling resistance. I think the fatter tires at lower pressures and tubular
tires are advantageous.

I have had a hard time going fast on bad buzzy road and cross riding on clumpy
uneven grass. Familiarity helped a lot. I still work on that, and it was work
getting used to pushing for speed on bad surfaces.

Ron

From: [email hidden] (Werehatrack)

Quoted message said:

Here in sunny, parched[1] Houston,
there is an additional reason to favor
tires of greater width, with my preference
being not to drop below 30mm; we have
*lots* of wide, open linear seams in our
streets, and wider tires traverse these
much more safely and predictably than
narrow ones.

Not much problems with road cuts, but we do have some RR crossings that
would send shivers up your spine, and I don't mean from road vibration
either!

- -
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

From: [email hidden] (BigBen)

Quoted message said:

Assuming we're talking about same
model of tyre, same tyre pressure, how
would that be any better than decreasing
the 23mm tyre pressure a bit - say, from
120 to 110 psi, for instance??

cheers,
jbr

Well, it would make for an even rougher ride for one, but the problem is
not so much road vibration as it is control. A 23mm tire wouldn't be any
wider that the gravel it's rolling over, and narrower tires tend to e
harder to keep on a line, as the road texture constantly tries to direct
it's direction of travel and the rider has to struggle more to keep the
bike riding straight.

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

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

To E-mail me:
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On Sun, 2 Jul 2006 15:38:25 -0400, [email hidden]

(Chris Z The Wheelman) said:

Well, it would make for an even rougher ride for one, but the problem is
not so much road vibration as it is control. A 23mm tire wouldn't be any
wider that the gravel it's rolling over, and narrower tires tend to e
harder to keep on a line, as the road texture constantly tries to direct
it's direction of travel and the rider has to struggle more to keep the
bike riding straight.

You don't think that droping tyre pressure a bit - 10 or 15 psi -
would make the contact surface of the tyre with the ground any wider??

And you think a 23mm tyre with less air pressure would be harsher? I
could swear I had the diferent feeling.

jbr