Fat tire riders look like "fat heads."

On Tue, 07 Jul 2020 07:20:22 +0700, John B.
wrote:

Doesn't wind resistance increase as a square of the velocity?

Yep. Wind resistance is drag and is proportional to the square of the
velocity. However, the energy needed to overcome that drag increases
with the cube of the velocity:
https://physics.info/drag/
See the section on "drag and power":
...if drag is proportional to the square of speed,
then the power needed to overcome that drag is proportional
to the cube of speed (P ? v3). You want to ride your
bicycle twice as fast, you'll have to be eight times
more powerful. This is why motorcycles are so much
faster than bicycles.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Tue, 07 Jul 2020 07:20:22 +0700, John B.
wrote:

Doesn't wind resistance increase as a square of the velocity?

Yep. Wind resistance is drag and is proportional to the square of the
velocity. However, the energy needed to overcome that drag increases
with the cube of the velocity:
https://physics.info/drag/
See the section on "drag and power":
...if drag is proportional to the square of speed,
then the power needed to overcome that drag is proportional
to the cube of speed (P ? v3). You want to ride your
bicycle twice as fast, you'll have to be eight times
more powerful. This is why motorcycles are so much
faster than bicycles.



Right, but you get there in half the time, so the energy required to go a
certain distance should go up as the square of the speed, once you reach a
velocity where aerodynamic drag dominates.

On Tue, 7 Jul 2020 00:52:05 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Mon, 6 Jul 2020 10:41:58 -0700 (PDT), Lou Holtman
wrote:

On Monday, July 6, 2020 at 7:15:32 PM UTC+2, Mark J. wrote:



It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with most
rides in the 30-33 range. Not, of course, on rides that start and end
at different elevations.


Tell that to the people that say that 10-20 Watt on average is insignificant.

Lou

Well, it is the difference between 0.01 and 0.02 H.P. :-)
--
Cheers,

John B.



If 1000 W = 1 HP, yes...

I believe that the usual calculation is 1 hp = 745.69987 watts.
--
Cheers,

John B.

John B. wrote:
On Tue, 7 Jul 2020 00:52:05 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Mon, 6 Jul 2020 10:41:58 -0700 (PDT), Lou Holtman
wrote:

On Monday, July 6, 2020 at 7:15:32 PM UTC+2, Mark J. wrote:



It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with most
rides in the 30-33 range. Not, of course, on rides that start and end
at different elevations.


Tell that to the people that say that 10-20 Watt on average is insignificant.

Lou

Well, it is the difference between 0.01 and 0.02 H.P. :-)
--
Cheers,

John B.



If 1000 W = 1 HP, yes...

I believe that the usual calculation is 1 hp = 745.69987 watts.
--
Cheers,

John B.



That’s what I thought too, but 1 HP = 1000 W was the only way to explain
your previous post. Maybe you’ve got better horses over there :-)

On 7/6/2020 5:20 PM, John B. wrote:
On Mon, 6 Jul 2020 10:15:27 -0700, "Mark J."
wrote:

On 7/5/2020 3:41 PM, Duane wrote:
Andre Jute wrote:
On Sunday, July 5, 2020 at 5:46:09 PM UTC+1, Jeff Liebermann wrote:
On Sat, 04 Jul 2020 19:21:20 -0700, Jeff Liebermann
wrote:

When you take the same rider and bike, and switch from slicks to
knobbies, you reduce the ground patch area. That increases the ground
pressure, which causes the rolling resistance to increase. That's one
reason why riding knobbies on pavement is like dragging an anchor.

I forgot to mumble something about tire pressu

"Everything You Think You Know About Bicycle Tire Pressure is Probably
Wrong"
https://www.roadbikerider.com/the-tire-pressure-revolution-by-jan-heine-d1/
Quoting:
Tire pressure has almost no effect on a tire’s speed.

If lower pressures don’t make tires slower, then you
can create wide tires with supple casings. You run
them at lower pressures, and you don’t give up any
performance on smooth roads. On rough roads, you
actually gain speed, because the tire (and you) bounce
less. And on all roads, you are more comfortable.

Conclusion
Tire pressure does not significantly affect your
bike’s rolling resistance, but the casing construction
of your tires does. This means that you can ride lower
pressures without going slower, and that wide tires
are no slower than narrow ones - as long as they have
similar casings. The fastest tires have supple casings
that consume less energy when they flex, and transmit
fewer vibrations, creating a win-win situation. These
tires roll super-fast no matter at what pressure you
run them.

So, you have a choice. A hard stiff narrow tire at high pressure or
a soft flexible wide tire at low pressure.

I'm not surprised, Jeff. Comparing the standard and the lightweight
folding Big Apples, and the thinner T19A tubes with the standard T19
tubes for 60x622 tyres, I found the lightweight versions to be very much
more comfortable with no degradation in handling and roadholding at the
limit, and not more fragile either on my rough but tarmacced lanes.
Handling is what the tyre does that is expected in response to normal
inputs up to the margin of error, roadholding is recovery from something
extreme stupid the rider does (or the road or environment does to him)
beyond the margin of error.

It must have been a common experience, because elements of the folding
Big Apple, and especially its ultra-flexible sidewall, were then spread
throughout the Big Apple range by Schwalbe, so that the folding tyre is
no longer a separate line within the brand.

Andre Jute
A life spent on the response of wheeled vehicles is not wasted. Sometimes
I wish I continued as a hot rodder all my life.


I tend to notice handling more than slight differences in rolling
resistance. Granted I’m not a racer trying to milk milliseconds from my
times. But cornering in a tight downhill is something I care about. My
HED wheels running 23mm conti folding tire at 90 psi are the sweet spot for
me. Comfortable and good handling. Just my two cents but I find the
discussion on rolling resistance without handling considered to be a bit
useless.

For a very different perspective, yesterday I took the gravel bike out
for a spin.

On the gravel bike - on gravel - rolling resistance takes on a much more
dominant role. Handling is more of an issue than on pavement. Never
mind efficiency, a harder/narrower rear tire gives so much bouncing and
skittering side-to-side that /control/ takes a lot more effort - and I'm
talking about riding in a straight line! I've found that good side lugs
on a tire help with the skittering - feels like the tire stays on top of
pieces of gravel rather than riding up and falling off sideways.

I've written before that the gravel in my county is pretty rough, though
that seems to vary by the week. Sometimes I'll find a nice hard-pack
track down the middle of the road, but I think the county just re-spread
gravel, 'cause it was all loose stuff yesterday.

There's no doubt I'm sinking a lot more energy into rolling resistance
than on a road bike. I can even quantify it a bit, being a data junkie
and having PowerTap wheels on both road and gravel bikes. On the road,
it takes a very brisk ride to burn over about 33-34 kiloJoules per mile.
Yesterday on the gravel, at a much lower speed, I averaged 35 kJ/mile.
This is for rides that start and end at the same elevation.

It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with most
rides in the 30-33 range. Not, of course, on rides that start and end
at different elevations.

Doesn't wind resistance increase as a square of the velocity?

That seems to be the consensus, yes, for the *force* of wind resistance.
Power is force x velocity, so it's proportional to the cube of velocity.

Mark J.

On 7/6/2020 7:19 PM, Ralph Barone wrote:
Jeff Liebermann wrote:
On Tue, 07 Jul 2020 07:20:22 +0700, John B.
wrote:

Doesn't wind resistance increase as a square of the velocity?

Yep. Wind resistance is drag and is proportional to the square of the
velocity. However, the energy needed to overcome that drag increases
with the cube of the velocity:
https://physics.info/drag/
See the section on "drag and power":
...if drag is proportional to the square of speed,
then the power needed to overcome that drag is proportional
to the cube of speed (P ? v3). You want to ride your
bicycle twice as fast, you'll have to be eight times
more powerful. This is why motorcycles are so much
faster than bicycles.



Right, but you get there in half the time, so the energy required to go a
certain distance should go up as the square of the speed, once you reach a
velocity where aerodynamic drag dominates.


Good point, fits with Frank's observation also.

Mark J.

On 7/6/2020 5:40 PM, Frank Krygowski wrote:
On 7/6/2020 1:15 PM, Mark J. wrote:


There's no doubt I'm sinking a lot more energy into rolling resistance
than on a road bike.Â* I can even quantify it a bit, being a data
junkie and having PowerTap wheels on both road and gravel bikes.Â* On
the road, it takes a very brisk ride to burn over about 33-34
kiloJoules per mile. Â*Â*Yesterday on the gravel, at a much lower speed,
I averaged 35 kJ/mile. Â*Â*This is for rides that start and end at the
same elevation.

It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with
most rides in the 30-33 range.Â* Not, of course, on rides that start
and end at different elevations.

I don't recall coming across kJ/mile numbers before, but looking at the
units, they reduce to units of force. So what those numbers represent is
the average force applied to drive the bike forward over the course of
the ride. So that would equal the total drag force on the bike, more or
less - rolling resistance, air resistance, what's lost in jiggling the
rider's body, etc.

Working the conversions, I get 30 kJ/mile = 18.6 Newtons force, or 4.2
pounds drag force on the bike, on average.

Air drag varies as the square of speed; but I'd expect for a reasonable
variation in low-ish speeds, the air drag would be at least fairly
constant. I'm assuming you're not riding over 20 mph.

Generally not, unless downhill/downwind.

That's an interesting way to think about it. I've mostly been crudely
equating kJ/mile with Cal/mile - that's Cal *input*, *not* output -
since ~25% biomechanical efficiency of cycling means 1 Cal input ~= 1 kJ
output. [1 Cal = 1 kcal = 4.184 kJ]. So I've been taking a very
different point of view.

Several years back I was teaching a freshman course that included
dimensional analysis and unit conversion. Being only a little creative
you can "convert" cookies eaten into miles cycled. I showed 'em that
one big cookie will get you 10 miles down the road. A student replied
"no way that's right." Cycling is vastly more efficient than most
people realize.

Mark J.

On Tue, 7 Jul 2020 03:56:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Tue, 7 Jul 2020 00:52:05 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Mon, 6 Jul 2020 10:41:58 -0700 (PDT), Lou Holtman
wrote:

On Monday, July 6, 2020 at 7:15:32 PM UTC+2, Mark J. wrote:



It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with most
rides in the 30-33 range. Not, of course, on rides that start and end
at different elevations.


Tell that to the people that say that 10-20 Watt on average is insignificant.

Lou

Well, it is the difference between 0.01 and 0.02 H.P. :-)
--
Cheers,

John B.



If 1000 W = 1 HP, yes...

I believe that the usual calculation is 1 hp = 745.69987 watts.
--
Cheers,

John B.



That’s what I thought too, but 1 HP = 1000 W was the only way to explain
your previous post. Maybe you’ve got better horses over there :-)


Well granted I did round a fairly lengthy number but no, 1 hp /
745.69987 watts = 0.0013410220896 hp.
So 10 watts is actual 0.013410220896 hp and 20 watts = 0.0268204417919
hp
--
Cheers,

John B.

On 7/6/2020 10:19 PM, Ralph Barone wrote:
Jeff Liebermann wrote:
On Tue, 07 Jul 2020 07:20:22 +0700, John B.
wrote:

Doesn't wind resistance increase as a square of the velocity?

Yep. Wind resistance is drag and is proportional to the square of the
velocity. However, the energy needed to overcome that drag increases
with the cube of the velocity:
https://physics.info/drag/
See the section on "drag and power":
...if drag is proportional to the square of speed,
then the power needed to overcome that drag is proportional
to the cube of speed (P ? v3). You want to ride your
bicycle twice as fast, you'll have to be eight times
more powerful. This is why motorcycles are so much
faster than bicycles.



Right, but you get there in half the time, so the energy required to go a
certain distance should go up as the square of the speed, once you reach a
velocity where aerodynamic drag dominates.

I'd leave Time out of it.

I'd just say that Energy, like Work, is Force times Distance. If you
were to double your speed, the Force required would indeed increase by a
factor of 4 (i.e. the square of speed, as you said). Multiplying that by
the same distance traveled yields four times the Work (or Energy) required.

I'm sure there are other ways of thinking about this, but my explanation
seems simplest to me.


--
- Frank Krygowski

On 7/6/2020 11:57 PM, Mark J. wrote:
On 7/6/2020 5:20 PM, John B. wrote:
On Mon, 6 Jul 2020 10:15:27 -0700, "Mark J."
wrote:

On 7/5/2020 3:41 PM, Duane wrote:
Andre Jute wrote:
On Sunday, July 5, 2020 at 5:46:09 PM UTC+1, Jeff Liebermann wrote:
On Sat, 04 Jul 2020 19:21:20 -0700, Jeff Liebermann

wrote:

When you take the same rider and bike, and switch from slicks to
knobbies, you reduce the ground patch area.Â* That increases the
ground
pressure, which causes the rolling resistance to increase.
That's one
reason why riding knobbies on pavement is like dragging an anchor.

I forgot to mumble something about tire pressu

"Everything You Think You Know About Bicycle Tire Pressure is
Probably
Wrong"
https://www.roadbikerider.com/the-tire-pressure-revolution-by-jan-heine-d1/

Quoting:
Tire pressure has almost no effect on a tire’s speed.

If lower pressures don’t make tires slower, then you
can create wide tires with supple casings. You run
them at lower pressures, and you don’t give up any
performance on smooth roads. On rough roads, you
actually gain speed, because the tire (and you) bounce
less. And on all roads, you are more comfortable.

Conclusion
Tire pressure does not significantly affect your
bike’s rolling resistance, but the casing construction
of your tires does. This means that you can ride lower
pressures without going slower, and that wide tires
are no slower than narrow ones - as long as they have
similar casings. The fastest tires have supple casings
that consume less energy when they flex, and transmit
fewer vibrations, creating a win-win situation. These
tires roll super-fast no matter at what pressure you
run them.

So, you have a choice.Â* A hard stiff narrow tire at high pressure or
a soft flexible wide tire at low pressure.
I'm not surprised, Jeff. Comparing the standard and the lightweight
folding Big Apples, and the thinner T19A tubes with the standard T19
tubes for 60x622 tyres, I found the lightweight versions to be very
much
more comfortable with no degradation in handling and roadholding at
the
limit, and not more fragile either on my rough but tarmacced lanes.
Handling is what the tyre does that is expected in response to normal
inputs up to the margin of error, roadholding is recovery from
something
extreme stupid the rider does (or the road or environment does to him)
beyond the margin of error.

It must have been a common experience, because elements of the folding
Big Apple, and especially its ultra-flexible sidewall, were then
spread
throughout the Big Apple range by Schwalbe, so that the folding
tyre is
no longer a separate line within the brand.

Andre Jute
A life spent on the response of wheeled vehicles is not wasted.
Sometimes
I wish I continued as a hot rodder all my life.


I tend to notice handling more than slight differences in rolling
resistance.Â* Granted I’m not a racer trying to milk milliseconds
from my
times.Â* But cornering in a tight downhill is something I care
about.Â* My
HED wheels running 23mm conti folding tire at 90 psi are the sweet
spot for
me.Â* Comfortable and good handling.Â*Â* Just my two cents but I find the
discussion on rolling resistance without handling considered to be a
bit
useless.

For a very different perspective, yesterday I took the gravel bike out
for a spin.

On the gravel bike - on gravel - rolling resistance takes on a much more
dominant role.Â* Handling is more of an issue than on pavement.Â* Never
mind efficiency, a harder/narrower rear tire gives so much bouncing and
skittering side-to-side that /control/ takes a lot more effort - and I'm
talking about riding in a straight line!Â* I've found that good side lugs
on a tire help with the skittering - feels like the tire stays on top of
pieces of gravel rather than riding up and falling off sideways.

I've written before that the gravel in my county is pretty rough, though
that seems to vary by the week.Â* Sometimes I'll find a nice hard-pack
track down the middle of the road, but I think the county just re-spread
gravel, 'cause it was all loose stuff yesterday.

There's no doubt I'm sinking a lot more energy into rolling resistance
than on a road bike.Â* I can even quantify it a bit, being a data junkie
and having PowerTap wheels on both road and gravel bikes.Â* On the road,
it takes a very brisk ride to burn over about 33-34 kiloJoules per mile.
Â* Yesterday on the gravel, at a much lower speed, I averaged 35 kJ/mile.
Â* This is for rides that start and end at the same elevation.

It's a topic for another post, but I find on the road that energy /per
mile/ is surprisingly consistent, ranging from around 27 kJ/mile for a
gentle pootle to maybe 35 kJ/mile for a very brisk hilly ride, with most
rides in the 30-33 range.Â* Not, of course, on rides that start and end
at different elevations.

Doesn't wind resistance increase as a square of the velocity?

That seems to be the consensus, yes, for the *force* of wind resistance.
Â*Power is force x velocity, so it's proportional to the cube of velocity.

+1


--
- Frank Krygowski