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Elliptical Chainrings



 
 
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  #11  
Old July 19th 13, 05:53 PM posted to rec.bicycles.racing
Sir Gregory Hall, Esq·
external usenet poster
 
Posts: 98
Default Elliptical Chainrings

"none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in message
...
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?


But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.



True, but *overall* diameter doesn't change as the number
of teeth remains the same. So, the gear ratio remains the
same. And, as long as the chainring radius is no greater than
that of the crank arm there isn't even any leverage difference
as if often the (erroneous) claim, due to the fact that it's
the length of the crank arms that determines the lever arm.

--
Sir Gregory


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  #12  
Old July 19th 13, 05:59 PM posted to rec.bicycles.racing
Sir Gregory Hall, Esq·
external usenet poster
 
Posts: 98
Default Elliptical Chainrings

"Friso" wrote in message
...
Yannick Tremblay yatremblay@bel1lin202.(none) wrote:
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?

But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.


I think that's the point of Biopace and this new system (has it got a
name yet?). The strength needed to rotate 1 cycle is equal, but with an
elliptical chainring this strength is supposed to be more equally
distributed.

Given the way everything is shaking and non-smooth there must be an
effect. I would think this effect is negative, also given the silent
passing of Biopace, but given the performance of Froome that doesn't
make sense.

I wonder: is it still possible to stand up on your pedals when you're
going uphill, or is this why Froome is almost always sitting?




Froome mostly sits because any energy used moving the body
up and down when standing is energy wasted compared to
not lifting the body and staying seated. A bicycle is a machine
which should be used for best mechanical advantage. Standing
and running on the machine as opposed to being seated on the
machine and spinning both pushing and pulling causes the machine
to become more efficient. Lifting the pedals while seated causes
more total energy to be put into the machine than lifting when
standing which mostly works against the inertia of the body mass
thus moving the body up and down with the push-pull and this
disrupts the smooth turning of circles which is more efficient
than some jerky motion.

Froome seems to have this insight. Then there's the factor
of wind resistance. Every pro should know that standing
causes more wind resistance. Why stand when it's going
to cost you watts and wear you out prematurely?

It's high time pro cyclists started relying less on drugs and
more on using their heads.

--
Sir Gregory


  #13  
Old July 19th 13, 06:00 PM posted to rec.bicycles.racing
Sir Gregory Hall, Esq·
external usenet poster
 
Posts: 98
Default Elliptical Chainrings

"Steve Freides" wrote in message
...

[trim]

You misread what I wrote. I don't assume that a change in circumference
matters, either - you could accomplish the same thing with a larger or
smaller, but still round, pulley.

The reason tests cannot confirm that this idea works is simple - it doesn't.
Neither the rear wheel nor your legs care about the shape of the chainring.
When you're pulling one tooth's worth of chain, that's what you're doing,
period!




BINGO!!!


  #14  
Old July 19th 13, 06:06 PM posted to rec.bicycles.racing
none
external usenet poster
 
Posts: 13
Default Elliptical Chainrings

In article ,
Friso wrote:
Yannick Tremblay yatremblay@bel1lin202.(none) wrote:
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?

But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.


I think that's the point of Biopace and this new system (has it got a
name yet?). The strength needed to rotate 1 cycle is equal, but with an
elliptical chainring this strength is supposed to be more equally
distributed.


The key is that the human ability to deliver power and generate torque
varies depending on the position of the pedals.

If you had a human with perfect spinning pedalling movement able to
generate the same amount of torque at every points over 360 degs then
these system would be useless. But they are an attempt to compensate
for the imperfect human engine (and pedals).

Given the way everything is shaking and non-smooth there must be an
effect. I would think this effect is negative, also given the silent
passing of Biopace, but given the performance of Froome that doesn't
make sense.


Why would you think that they have a negative effect?

Shimano, Rotors, and the like have made scientific studies on the
subject. We could dismiss some of it as marketing gimmick, other as
flawed science but I would not dismiss the Sky team and David
Brailsford.

The UK cycling team has achieved so much success in the Olympics and
WC in large part by preparing and training better, harder and more
scientifically than anyone else. Team Sky is most probably the most
scientifically trained and tested team. I would be incredibly
surprised if Chris Froome has not spent hundreds of hours on a
training bikes in the lab trying different setup including circular
chain rig and ovoid chain rig. The difference may have been only 0.5%
or even less but Brailsford believes in summing all these small minor
advantages and making it a winning difference.

I wouldn't even be surprised that the exact angle of the ovoid for
Froome differs between his mountain climbing bike and his time trial
bike and that they all differ from Wiggins ones all of that based on
labs measurement for the specific athlete under specific conditions.
Brailsford and his team are that anal with regards to details.

In act, the above probably highlight one of the problem with Biopace
in that it was one setup that may have been good for a certain type of
rider with a certain pedalling style but not for a different rider with
a different pedalling style.

I wonder: is it still possible to stand up on your pedals when you're
going uphill, or is this why Froome is almost always sitting?


Hmm, not sure. In theory "dancing on a bike" is not very good and a
waste of effort in the long term although climbers like to do it for
short efforts. I don't seem to recall someone like Indurain standing
up too often either. I'd put it down to riding style.

Yani

  #15  
Old July 19th 13, 06:20 PM posted to rec.bicycles.racing
Sir Gregory Hall, Esq·
external usenet poster
 
Posts: 98
Default Elliptical Chainrings

" Sir Gregory Hall, Esq·" åke wrote in message
...
"Friso" wrote in message
...
Yannick Tremblay yatremblay@bel1lin202.(none) wrote:
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?

But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.

For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.


I think that's the point of Biopace and this new system (has it got a
name yet?). The strength needed to rotate 1 cycle is equal, but with an
elliptical chainring this strength is supposed to be more equally
distributed.

Given the way everything is shaking and non-smooth there must be an
effect. I would think this effect is negative, also given the silent
passing of Biopace, but given the performance of Froome that doesn't
make sense.

I wonder: is it still possible to stand up on your pedals when you're
going uphill, or is this why Froome is almost always sitting?




Froome mostly sits because any energy used moving the body
up and down when standing is energy wasted compared to
not lifting the body and staying seated. A bicycle is a machine
which should be used for best mechanical advantage. Standing
and running on the machine as opposed to being seated on the
machine and spinning both pushing and pulling causes the machine


to become (correction) LESS efficient. Lifting the pedals while seated
causes


more total energy to be put into the machine than lifting when
standing which mostly works against the inertia of the body mass
thus moving the body up and down with the push-pull and this
disrupts the smooth turning of circles which is more efficient
than some jerky motion.

Froome seems to have this insight. Then there's the factor
of wind resistance. Every pro should know that standing
causes more wind resistance. Why stand when it's going
to cost you watts and wear you out prematurely?

It's high time pro cyclists started relying less on drugs and
more on using their heads.

--
Sir Gregory




  #16  
Old July 19th 13, 06:55 PM posted to rec.bicycles.racing
none
external usenet poster
 
Posts: 13
Default Elliptical Chainrings

In article ,
Steve Freides wrote:
none (Yannick Tremblay) wrote:
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the
gear ratio? Forget the number of teeth, they're only there 'cos a
chain is used. Think of diameter. Variable diameter. Honest. Think
drive belt? Big pulley vs small pulley?

But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the
difference what the shape is? For a belt driven system, a change in
shape could at least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely
correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.

Yan


You misread what I wrote. I don't assume that a change in circumference
matters, either - you could accomplish the same thing with a larger or
smaller, but still round, pulley.

The reason tests cannot confirm that this idea works is simple - it
doesn't. Neither the rear wheel nor your legs care about the shape of
the chainring. When you're pulling one tooth's worth of chain, that's
what you're doing, period.


"When you're pulling one tooth's worth of chain"

Yes absolutely, for the *rear* cog. But how many degree of rotation
of the pedals are needed to move 1 tooth at the back?

On a circular chain rig, pulling 1 tooth of the front 36 rig
will pull 1 teeth of the rear 18 cog. This occurs on a 10 degree
rotation of the pedals regardless of the pedal position and causes a
20 degree rotation of the rear wheel.

On an ovoid chain rig however, this is not the case. While the ovoid
rotate 10 degree, its active diameter also changes. The change in
active diameter of the front can be observed by looking at the
derailler moving in an out as the front rig rotates. It is kind of
equivalent to the front rig dynamically changing between, say 35 and 37
teeth during a full rotation. (This is possible because only about
half of the front rig is touching the chain at any point in time and
there is slack in the chain). For some section of the rotation the
chain is being pulled by the rotation and is getting pulled also by
the increase in diameter while for other sections, the chain will be
pulled by the rotation but some of this will be cancelled by the
reduction in diameter. So while 360 deg front = 720 degs rear,
for some part of the rotation, 10 degree front could result in 19.5 or
20.5 degs rear (because the chain is also being pulled by the increase
in diameter) rather than a constant 20 degree. There is a difference
and this difference can be measured.

The mechanics of ovoid/biopace/etc are pretty easy to demonstrate
experimentally or prove mathematically.

What is a lot less clear are the real benefits to the cyclists.


Yan
  #17  
Old July 19th 13, 07:09 PM posted to rec.bicycles.racing
none
external usenet poster
 
Posts: 13
Default Elliptical Chainrings

In article ,
Sir Gregory Hall, Esq· åke wrote:
"none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in message
...
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?

But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.



True, but *overall* diameter doesn't change as the number
of teeth remains the same. So, the gear ratio remains the
same. And, as long as the chainring radius is no greater than
that of the crank arm there isn't even any leverage difference
as if often the (erroneous) claim, due to the fact that it's
the length of the crank arms that determines the lever arm.


Please, this is pure mathematics and mechanics.

The "active" "current" diameter of the front rig changes dynamically
during a rotation which means that the current amount of rotation
of the pedal that is needs to achieve some specific rotation of
the rear wheel with the pedal-crank-rig-chain-cog-wheel assembly
changes dynamically. In average over 360 degree it is the same but
instantaneously it differs.

The problem and complexity occurs when you start introducing a bloody
human in the equation and these pesky things are pretty much impossible
to model mathematically and are notoriously irregular between
individuals.

Serously, by all mean disagree that it has any benefits to humans (I
am certainly not convinced either) but lets not disagree on
mathematics.

Yan


  #18  
Old July 19th 13, 07:35 PM posted to rec.bicycles.racing
Sir Gregory Hall, Esq·
external usenet poster
 
Posts: 98
Default Elliptical Chainrings

"none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in
message ...

On an ovoid chain rig however, this is not the case. While the ovoid
rotate 10 degree, its active diameter also changes.


Active diameter doesn't matter. Only the gear ratio matters and
that gear ration depends on number of teeth.

The change in
active diameter of the front can be observed by looking at the
derailler moving in an out as the front rig rotates. It is kind of
equivalent to the front rig dynamically changing between, say 35 and 37
teeth during a full rotation. (This is possible because only about
half of the front rig is touching the chain at any point in time and
there is slack in the chain).


Wrong! The gear ration doesn't change. Only the slack in the chain
changes depending upon the position of the shape of the chainring.
The derailleur pulleys are a chain tensioner so of course when the
chain becomes slack it takes up the slack. This doesn't mean the
gear ratio is changing. One could use a square or rectangular
chainring but if it had 53 teeth then the shape of it won't change
the gear ratio. It is gear ratio that determines mechanical advantage
not gear shape. Oddly shaped gears only result in reduced efficiency
compared to circular gears.


--
Sir Gregory


  #19  
Old July 19th 13, 09:20 PM posted to rec.bicycles.racing
Mower Man
external usenet poster
 
Posts: 109
Default Elliptical Chainrings

On 18/07/2013 11:04 PM, Steve Freides wrote:
Mower Man wrote:
On 18/07/2013 9:26 PM, Steve Freides wrote:
Davey Crockett wrote:
" Sir Gregory Hall, Esq·" a écrit profondement:

Elliptical chainrings are a GIMMICK. Why?

Because gearing depends upon the number of teeth on
the chainring and the number of teeth on the cassette.

When spinning the crankshaft it doesn't matter one iota
what shape the chainring is. All that matters is the
relationship between the number of teeth on the
chainring and the number of teeth on the particular
cassette ring.

Any idiot who thinks otherwise is just that, an idiot!

The original concept, way back, was that the eliptical shape
allowed one to transmit the same, or reasoably the same, power to
the drive train whether the cranks were at TDC, BDC or any other
aspect.

(TDC=Top Dead Center)

Wouldn't it make more sense, then for the pedaling circle to be
elliptical, rather than the chainrings? I'm not quite sure how one
would achieve that end, but Sir Gregory Hall seems to have a point
here - if you're still pedaling circles, it doesn't matter how the
chainrings are shaped.

Davey remembers Jeff Bernard proudly sporting the "BioPace" decal
on his regular (round) chainring. He didn't believe the Shimano BS
either apparently.

Ah, yes, I did try BioPace back in the day. NB: they, nor any other
non-round chainrings, are terribly useful on a fixed gear.

-S-


Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?


But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.

-S-


See next post - totally correct!

--
Chris

'Fashion is a form of ugliness so intolerable that we have to alter it
every six months.'

(Oscar Wilde.)
  #20  
Old July 19th 13, 09:20 PM posted to rec.bicycles.racing
Mower Man
external usenet poster
 
Posts: 109
Default Elliptical Chainrings

On 19/07/2013 10:45 AM, none Yannick Tremblay wrote:
In article ,
Steve Freides wrote:
Mower Man wrote:

Isn't it the point that elliptical chain rings actually vary the gear
ratio? Forget the number of teeth, they're only there 'cos a chain is
used. Think of diameter. Variable diameter. Honest. Think drive belt?
Big pulley vs small pulley?


But big pulley versus small pulley, first of all, means something
different for belt drive than for one with teeth. If one pedal
revolution gets you 39 teeth spaced evenly apart, what's the difference
what the shape is? For a belt driven system, a change in shape could at
least mean a change in circumference.


For 1 complete revolution, there is no difference. Absolutely correct.

However what about 1/4 of a revolution or 1/8 of a revolution? Then
the diameter of the "big pulley" does differs.

Yan


Spot on. That's how it works.


--
Chris

'Fashion is a form of ugliness so intolerable that we have to alter it
every six months.'

(Oscar Wilde.)
 




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