Help with static vs apparent mass of rotating wheel

[[email protected]]

On Nov 28, 11:15 pm, [email protected] wrote:
> On Wed, 28 Nov 2007 12:47:43 -0800 (PST),
>
> "[email protected]" <[email protected]> wrote:
>
> [snip]
>
> >Not at all. The guy who agreed to participate in our dumbell test had
> >at the time the same power output as I did, based on calculations we
> >did for 10km TT's we rode. He is smaller than me and weighed about
> >75kg. We put 25kg into the backpack.
>
> [snip]
>
> Dear Joseph,
>
> Sometimes I'm amazed by the details that people forget to mention
> until deep in a thread.
>
> Don't you think that just sitting up with a 25 kg (55 pound) backpack
> might demand a bit of the 75 kg rider's power before he even starts to
> pedal?
>
> That is, a 55 pound weight on your back is not the same thing as a 55
> pound weight on a luggage rack.
>
> You put out X watts _while_ holding up a 100 kg body.
>
> Your friend puts out X watts while holding up only a 75 kg body.
>
> But just holding up the extra 55 pounds awkwardly placed on his back
> is going to reduce the watts available to push on the pedals.
>
> This is the kind of thing that led a famous British trials rider to
> shake his head at the sight of clueless U.S. amateurs wearing
> jumpsuits with endless pockets full of metal tools and spares.
>
> (Hey, I was only 16 and just doing what everyone else did. Besides, an
> orange jumpsuit looked cool, even if my neck was sore for some reason
> after riding around with a few pounds of wrenches, spare tubes, and
> other stuff pulling down on my collar.)
>
> Cargo should be carried by the bicycle (or motorcycle), not the rider.
>
> That's why touring bicycles come with luggage racks instead of
> backpacks, why cowboys laugh at innocents who climb onto horses while
> wearing knapsacks, and why even young mothers learn to hang purses and
> infant paraphernalia on the baby carriages.
>
> Cheers,
>
> Carl Fogel

We thought about that, and it is was his pack he uses while skiing,
the weight was low mor eor less resting on his lower back, and we
remained seated while climbing. It wasn't exactly scientific, but the
difference was huge. We could try it on a rack and I'm sur eth e
results would be quite similar.

I don't believ the rider output is necessarily the same independent of
what type of resistance the legs meet. At high speed on a flat tt
course where the momentum is high, vs a steep hill at low speed where
the momentum is low.

Joseph

 

[[email protected]]

On Thu, 29 Nov 2007 01:31:51 -0800 (PST),
"[email protected]" <[email protected]> wrote:

>On Nov 28, 11:15 pm, [email protected] wrote:
>> On Wed, 28 Nov 2007 12:47:43 -0800 (PST),
>>
>> "[email protected]" <[email protected]> wrote:
>>
>> [snip]
>>
>> >Not at all. The guy who agreed to participate in our dumbell test had
>> >at the time the same power output as I did, based on calculations we
>> >did for 10km TT's we rode. He is smaller than me and weighed about
>> >75kg. We put 25kg into the backpack.
>>
>> [snip]
>>
>> Dear Joseph,
>>
>> Sometimes I'm amazed by the details that people forget to mention
>> until deep in a thread.
>>
>> Don't you think that just sitting up with a 25 kg (55 pound) backpack
>> might demand a bit of the 75 kg rider's power before he even starts to
>> pedal?
>>
>> That is, a 55 pound weight on your back is not the same thing as a 55
>> pound weight on a luggage rack.
>>
>> You put out X watts _while_ holding up a 100 kg body.
>>
>> Your friend puts out X watts while holding up only a 75 kg body.
>>
>> But just holding up the extra 55 pounds awkwardly placed on his back
>> is going to reduce the watts available to push on the pedals.
>>
>> This is the kind of thing that led a famous British trials rider to
>> shake his head at the sight of clueless U.S. amateurs wearing
>> jumpsuits with endless pockets full of metal tools and spares.
>>
>> (Hey, I was only 16 and just doing what everyone else did. Besides, an
>> orange jumpsuit looked cool, even if my neck was sore for some reason
>> after riding around with a few pounds of wrenches, spare tubes, and
>> other stuff pulling down on my collar.)
>>
>> Cargo should be carried by the bicycle (or motorcycle), not the rider.
>>
>> That's why touring bicycles come with luggage racks instead of
>> backpacks, why cowboys laugh at innocents who climb onto horses while
>> wearing knapsacks, and why even young mothers learn to hang purses and
>> infant paraphernalia on the baby carriages.
>>
>> Cheers,
>>
>> Carl Fogel
>
>We thought about that, and it is was his pack he uses while skiing,
>the weight was low mor eor less resting on his lower back, and we
>remained seated while climbing. It wasn't exactly scientific, but the
>difference was huge. We could try it on a rack and I'm sur eth e
>results would be quite similar.
>
>I don't believ the rider output is necessarily the same independent of
>what type of resistance the legs meet. At high speed on a flat tt
>course where the momentum is high, vs a steep hill at low speed where
>the momentum is low.
>
>Joseph

Dear Joseph,

I think that you needed to think more.

Cheers,

Carl Fogel

 

[[email protected]]

On Nov 29, 8:26 pm, [email protected] wrote:
> On Thu, 29 Nov 2007 01:31:51 -0800 (PST),
>
>
>
> "[email protected]" <[email protected]> wrote:
> >On Nov 28, 11:15 pm, [email protected] wrote:
> >> On Wed, 28 Nov 2007 12:47:43 -0800 (PST),
>
> >> "[email protected]" <[email protected]> wrote:
>
> >> [snip]
>
> >> >Not at all. The guy who agreed to participate in our dumbell test had
> >> >at the time the same power output as I did, based on calculations we
> >> >did for 10km TT's we rode. He is smaller than me and weighed about
> >> >75kg. We put 25kg into the backpack.
>
> >> [snip]
>
> >> Dear Joseph,
>
> >> Sometimes I'm amazed by the details that people forget to mention
> >> until deep in a thread.
>
> >> Don't you think that just sitting up with a 25 kg (55 pound) backpack
> >> might demand a bit of the 75 kg rider's power before he even starts to
> >> pedal?
>
> >> That is, a 55 pound weight on your back is not the same thing as a 55
> >> pound weight on a luggage rack.
>
> >> You put out X watts _while_ holding up a 100 kg body.
>
> >> Your friend puts out X watts while holding up only a 75 kg body.
>
> >> But just holding up the extra 55 pounds awkwardly placed on his back
> >> is going to reduce the watts available to push on the pedals.
>
> >> This is the kind of thing that led a famous British trials rider to
> >> shake his head at the sight of clueless U.S. amateurs wearing
> >> jumpsuits with endless pockets full of metal tools and spares.
>
> >> (Hey, I was only 16 and just doing what everyone else did. Besides, an
> >> orange jumpsuit looked cool, even if my neck was sore for some reason
> >> after riding around with a few pounds of wrenches, spare tubes, and
> >> other stuff pulling down on my collar.)
>
> >> Cargo should be carried by the bicycle (or motorcycle), not the rider.
>
> >> That's why touring bicycles come with luggage racks instead of
> >> backpacks, why cowboys laugh at innocents who climb onto horses while
> >> wearing knapsacks, and why even young mothers learn to hang purses and
> >> infant paraphernalia on the baby carriages.
>
> >> Cheers,
>
> >> Carl Fogel
>
> >We thought about that, and it is was his pack he uses while skiing,
> >the weight was low mor eor less resting on his lower back, and we
> >remained seated while climbing. It wasn't exactly scientific, but the
> >difference was huge. We could try it on a rack and I'm sur eth e
> >results would be quite similar.
>
> >I don't believ the rider output is necessarily the same independent of
> >what type of resistance the legs meet. At high speed on a flat tt
> >course where the momentum is high, vs a steep hill at low speed where
> >the momentum is low.
>
> >Joseph
>
> Dear Joseph,
>
> I think that you needed to think more.
>
> Cheers,
>
> Carl Fogel


Riding fast on flat ground at a given power output of 400W at 90rpm
means an average force on the pedals of about 25kg. Most of this force
is applied during a limited part of the pedal stroke. The momentum of
the rider means that this force need not be evenly applied. If the
force applied is significantly less during some part of the pedal
stroke, this does not affect the speed of the bike, nor does it
require any additional effort to reaccelerate the rider with each
fluctuation of pedal force.

Riding up a steep hill at 90 rpm and 400W also requires an average of
25kg force on the pedals. But in this case, the force must be more
evenly applied or else the bike slows significantly with each pedal
stroke. even if the bike is allowed to do so, the muscles are perhaps
required to do more work in portions of the pedal stroke than they
would do otherwise.

These two situations are different, and the latter favors muscle
strength. The latter is also more exaggerated the steeper the hill, or
the heavier the load. Lighter riders do not really feel these effects
until the going gets quite steep. Adding a huge amount of extra weight
brings them to this effect on not so steep roads and to uncharted
territory in terms of what their muscles can handle.

The 75kg rider was in much better aerobic condition than I (witnessed
by our having the same power output despite my significantly larger
size), but was nowhere near as strong. So when the extra weight meant
his muscles needed to provide more force in parts of the pedals stroke
he was not used to needing, it sapped his energy.

Joseph

 

[[email protected]]

On Thu, 29 Nov 2007 12:04:11 -0800 (PST),
"[email protected]" <[email protected]> wrote:

>On Nov 29, 8:26 pm, [email protected] wrote:
>> On Thu, 29 Nov 2007 01:31:51 -0800 (PST),
>>
>>
>>
>> "[email protected]" <[email protected]> wrote:
>> >On Nov 28, 11:15 pm, [email protected] wrote:
>> >> On Wed, 28 Nov 2007 12:47:43 -0800 (PST),
>>
>> >> "[email protected]" <[email protected]> wrote:
>>
>> >> [snip]
>>
>> >> >Not at all. The guy who agreed to participate in our dumbell test had
>> >> >at the time the same power output as I did, based on calculations we
>> >> >did for 10km TT's we rode. He is smaller than me and weighed about
>> >> >75kg. We put 25kg into the backpack.
>>
>> >> [snip]
>>
>> >> Dear Joseph,
>>
>> >> Sometimes I'm amazed by the details that people forget to mention
>> >> until deep in a thread.
>>
>> >> Don't you think that just sitting up with a 25 kg (55 pound) backpack
>> >> might demand a bit of the 75 kg rider's power before he even starts to
>> >> pedal?
>>
>> >> That is, a 55 pound weight on your back is not the same thing as a 55
>> >> pound weight on a luggage rack.
>>
>> >> You put out X watts _while_ holding up a 100 kg body.
>>
>> >> Your friend puts out X watts while holding up only a 75 kg body.
>>
>> >> But just holding up the extra 55 pounds awkwardly placed on his back
>> >> is going to reduce the watts available to push on the pedals.
>>
>> >> This is the kind of thing that led a famous British trials rider to
>> >> shake his head at the sight of clueless U.S. amateurs wearing
>> >> jumpsuits with endless pockets full of metal tools and spares.
>>
>> >> (Hey, I was only 16 and just doing what everyone else did. Besides, an
>> >> orange jumpsuit looked cool, even if my neck was sore for some reason
>> >> after riding around with a few pounds of wrenches, spare tubes, and
>> >> other stuff pulling down on my collar.)
>>
>> >> Cargo should be carried by the bicycle (or motorcycle), not the rider.
>>
>> >> That's why touring bicycles come with luggage racks instead of
>> >> backpacks, why cowboys laugh at innocents who climb onto horses while
>> >> wearing knapsacks, and why even young mothers learn to hang purses and
>> >> infant paraphernalia on the baby carriages.
>>
>> >> Cheers,
>>
>> >> Carl Fogel
>>
>> >We thought about that, and it is was his pack he uses while skiing,
>> >the weight was low mor eor less resting on his lower back, and we
>> >remained seated while climbing. It wasn't exactly scientific, but the
>> >difference was huge. We could try it on a rack and I'm sur eth e
>> >results would be quite similar.
>>
>> >I don't believ the rider output is necessarily the same independent of
>> >what type of resistance the legs meet. At high speed on a flat tt
>> >course where the momentum is high, vs a steep hill at low speed where
>> >the momentum is low.
>>
>> >Joseph
>>
>> Dear Joseph,
>>
>> I think that you needed to think more.
>>
>> Cheers,
>>
>> Carl Fogel
>
>
>Riding fast on flat ground at a given power output of 400W at 90rpm
>means an average force on the pedals of about 25kg. Most of this force
>is applied during a limited part of the pedal stroke. The momentum of
>the rider means that this force need not be evenly applied. If the
>force applied is significantly less during some part of the pedal
>stroke, this does not affect the speed of the bike, nor does it
>require any additional effort to reaccelerate the rider with each
>fluctuation of pedal force.
>
>Riding up a steep hill at 90 rpm and 400W also requires an average of
>25kg force on the pedals. But in this case, the force must be more
>evenly applied or else the bike slows significantly with each pedal
>stroke. even if the bike is allowed to do so, the muscles are perhaps
>required to do more work in portions of the pedal stroke than they
>would do otherwise.
>
>These two situations are different, and the latter favors muscle
>strength. The latter is also more exaggerated the steeper the hill, or
>the heavier the load. Lighter riders do not really feel these effects
>until the going gets quite steep. Adding a huge amount of extra weight
>brings them to this effect on not so steep roads and to uncharted
>territory in terms of what their muscles can handle.
>
>The 75kg rider was in much better aerobic condition than I (witnessed
>by our having the same power output despite my significantly larger
>size), but was nowhere near as strong. So when the extra weight meant
>his muscles needed to provide more force in parts of the pedals stroke
>he was not used to needing, it sapped his energy.
>
>Joseph

Dear Joseph,

I meant that I think that you need to think more about the effect of
55 pounds of extra weight sitting on the back of a 165-lb rider
instead of sitting on a luggage rack.

Cheers,

Carl Fogel

 

[Ben C]

On 2007-11-29, [email protected] <[email protected]> wrote:
[...]
> Riding fast on flat ground at a given power output of 400W at 90rpm
> means an average force on the pedals of about 25kg. Most of this force
> is applied during a limited part of the pedal stroke. The momentum of
> the rider means that this force need not be evenly applied. If the
> force applied is significantly less during some part of the pedal
> stroke, this does not affect the speed of the bike, nor does it
> require any additional effort to reaccelerate the rider with each
> fluctuation of pedal force.

I don't think the effect is momentum, but because of the way the
resistive power varies with speed.

We're comparing a hill (constant gradient) to the flat, but 400W, 90rpm
and constant speed in both cases (so going faster on the flat).
Resistive power is the same: 400W.

Slow down a bit and resistive power drops a bit. On the hill resistive
power is proportional to speed. On the flat, it's proportional to speed
cubed (roughly).

In other words, slow down a bit and it gets easier, but by much more on
the flat than on the hill.

I think that's why the flat feels easier and why you don't feel like
you're starting to go backwards if you slack off for an instant.

 

[[email protected]]

On Nov 29, 10:39 pm, Ben C <[email protected]> wrote:
> On 2007-11-29, [email protected] <[email protected]> wrote:
> [...]
>
> > Riding fast on flat ground at a given power output of 400W at 90rpm
> > means an average force on the pedals of about 25kg. Most of this force
> > is applied during a limited part of the pedal stroke. The momentum of
> > the rider means that this force need not be evenly applied. If the
> > force applied is significantly less during some part of the pedal
> > stroke, this does not affect the speed of the bike, nor does it
> > require any additional effort to reaccelerate the rider with each
> > fluctuation of pedal force.
>
> I don't think the effect is momentum, but because of the way the
> resistive power varies with speed.
>
> We're comparing a hill (constant gradient) to the flat, but 400W, 90rpm
> and constant speed in both cases (so going faster on the flat).
> Resistive power is the same: 400W.

I guess I mean to say that perhaps someone who can put out 400W on the
flats at 90rpm, might not be able to do so at 90rpm on a wicked steep
hill or with additional weight.

> Slow down a bit and resistive power drops a bit. On the hill resistive
> power is proportional to speed. On the flat, it's proportional to speed
> cubed (roughly).
>
> In other words, slow down a bit and it gets easier, but by much more on
> the flat than on the hill.
>
> I think that's why the flat feels easier and why you don't feel like
> you're starting to go backwards if you slack off for an instant.

You don't feel like you are going backwards because you have momentum
due to speed, and what momentum you have isn't being sapped by a
gradient.

I believe flats feel easier due to this momentum and because on the
flats you can be more (unconsciously) selective about where you
concentrate your effort in the pedal stroke.

Joseph

 

[[email protected]]

On Nov 29, 5:16 pm, "[email protected]"
<[email protected]> wrote:
>
>
> I guess I mean to say that perhaps someone who can put out 400W on the
> flats at 90rpm, might not be able to do so at 90rpm on a wicked steep
> hill or with additional weight.

That doesn't seem at all obvious to me. And while it's not precisely
what you're saying, I believe almost all riders put out more power,
not less, while climbing hills. I think that's true of almost all
competitive rides, not only casual rides.

I suppose we could figure this out if we had data on speeds on the
flat, compared to speeds uphill.

> You don't feel like you are going backwards because you have momentum
> due to speed, and what momentum you have isn't being sapped by a
> gradient.

What you seem to be implying is that power output of a cyclist's legs
is significantly reduced by changes in angular velocity of the cranks
during the pedal stroke.

That's the sort of thing that an exercise physiologist might study in
detail, if it were known to exist. But I've certainly never heard of
such a thing. And I'll note that changing other factors affecting the
crank motion - for example, crank length - seem to have negligible
effect.

- Frank Krygowski

 

[[email protected]]

On Nov 30, 1:05 am, [email protected] wrote:
> On Nov 29, 5:16 pm, "[email protected]"
>
> <[email protected]> wrote:
>
> > I guess I mean to say that perhaps someone who can put out 400W on the
> > flats at 90rpm, might not be able to do so at 90rpm on a wicked steep
> > hill or with additional weight.
>
> That doesn't seem at all obvious to me. And while it's not precisely
> what you're saying, I believe almost all riders put out more power,
> not less, while climbing hills. I think that's true of almost all
> competitive rides, not only casual rides.

I suppose I meant that the power outputs might be different. Not that
flat would necessarily be more.

On the flats you don't need to apply nearly any force at the very top
of the pedal stroke, but on steep climbs with near zero momentum you
need to apply quite a bit more, and the heavier and/or steeper, the
more required. I think this muscle usage pattern is different than on
the flats where more of the force generation can be concentrated in
other parts of the pedal stroke. This may effect how much power a
rider is cabable of producing.

> I suppose we could figure this out if we had data on speeds on the
> flat, compared to speeds uphill.

Or everyone could pitch in and buy me a powermeter. I promise to
report back with lots of data!

>
> > You don't feel like you are going backwards because you have momentum
> > due to speed, and what momentum you have isn't being sapped by a
> > gradient.
>
> What you seem to be implying is that power output of a cyclist's legs
> is significantly reduced by changes in angular velocity of the cranks
> during the pedal stroke.

Maybe by changes in angular velocity, but certainly in what part of
the pedal stroke most of the effort is concentrated in. Think about
pedalling by ONLY pushing forward at the top of the stroke and
scraping the shoe at the bottom, no pushing in the normal way. How
much power could you produce? Could you exhaust yourself? I don't
know.

> That's the sort of thing that an exercise physiologist might study in
> detail, if it were known to exist. But I've certainly never heard of
> such a thing. And I'll note that changing other factors affecting the
> crank motion - for example, crank length - seem to have negligible
> effect.
>

It probably is just something that disappears in the noise, and is
covered by "ride lots".

Joseph

 

[[email protected]]

On Nov 29, 10:45 pm, [email protected] wrote:

>> Dear D,
>
> You keep mentioning a seven-second difference in a 40k TT.
>
> Please tell us what wheels were being compared.


Way back in the beginning of this thread, someone mentioned a
theoretical time savings...

<I tried a pair of G36 wheels, changing the weight to match, and the
calculator predicted 466.98 seconds for both.
Take 200 grams off each wheel on one bike, and the time drops to
466.29 seconds, about 7/10ths of a second faster for the slightly
lighter bike that accelerates slightly faster on a theoretical 4 km
TT
course with no theoretical braking.>

Seven seconds for 40k.

Continuing:

<In contrast, slightly heavier wheels with better aerodynamics (the
default for the right-hand bike) can take about 12 seconds off the
same time.>

Since I sometimes don't attribute very well, I'll ask for help in
finding where I was the one who dragged aero into the discussion.
Maybe I did! But my intended point lies elsewhere. --D-y

 

[[email protected]]

On Nov 28, 3:30 pm, "[email protected]" <[email protected]> wrote:
> On Nov 28, 3:35 am, "[email protected]"
>
> <[email protected]> wrote:
> > The wheels in question (not quite barbell territory, but still a big
> > difference):
>
> > 6600 hubs, Velocity Deep-V 28 and 32, DT Competition, brass, Vittoria
> > Pave, Continental tubes
> > vs
> > AC hubs, Mavic Oro-10 28, DT Revolution, alloy, Veloflex Criterium
>
> What is your reference or actual weight difference between these two
> sets of wheels?
>
> Given a minimum reliability for your size, fellow largeperson, those
> might be very nice to ride, other considerations aside. My last set of
> sewups were fun. I'll do it again sometime. The budget is elsewhere
> presently.

Since my scale is less precise than the cardboard box it came in, this
is theoretical weight:

2753 vs 1631 (including tires/tubes), or 2113 vs 1211 for just the
metal bits.

Joseph