Crank lengths

[Jose Rizal]

Mike:

> Jose Rizal wrote:
>
> >>Eh? constant angular velocity means constant cadence. 1 rad/s = 9.55 rpm
> >
> > No, you can achieve constant cadence without having constant angular velocity within one
> > revolution. Within one revolution, the crank angular velocity can (and in practice, does) vary,
> > but as long as this variation in speed is consistent with each revolution, the cadence will
>
> Sounds like biopace gears to me.

Huh? One of the reasonings behind Biopace is exactly the opposite of what you imply.

> Otherwise you are talking about the bike rapidly accelerating and decelerating, and thats
> just silly.

In simple terms, next time you ride a bicycle, try to see if you can apply a *constant* maximum
force within each revolution of the crank. This is next to impossible as your legs will apply a
variable force depending on the position of the pedal. When the cranks are vertical, it doesn't take
much brains to deduce that the force your legs can apply to the pedals will be less than when the
cranks are horizontal. Since this is the case, a variable force within each revolution of the pedal
means the crank rotational speed is not constant, even though cadence can be. If visual aids help
your comprehension, watch the start of a track race when it is easily seen that the bike and a
powerful rider will seem to surge ahead several times on the first few revolutions of the crank as
the bike picks up speed from rest.

> > stay the same. For example, the angular velocity may be at a peak when the cranks are horizontal
> > with one leg pushing down and the other
>
> Well, theoretically and immeasurably tinily.

Practically and measurably, but don't let reality spoil your musings.

> Actually, the peak speed is later, when pedal power drops below friction power. But of what
> possible relevance are these microscopic speed oscillations??

Actually, you're now engaging in mumbo-jumbo in trying to support your proclamations. Friction
power? Is this a new branch of physics you've invented?

> > But that is what you imply when you demand having constant pedal speed.
>
> No. I mean linear speed, not angular. It aint rocket science.

Which makes me wonder why and what part of all this you don't understand.

 

[Shabby]

Originally posted by Mike
Gemma, how about finding someone to try the 175mm cranks on a track bike? Be sure to stand by with a
camera to document the results, and post here!
[/B]

On behalf of Gemma, I'd like to point out that Brad McGee won the Commonwealth games gold medal in the pursuit on 175mm cranks. Good enough for you?

When you are going fast you are perpendicular to the track anyway.

http://www.cyclingnews.com/teamprofiles/2001/brad_mcgee.shtml

 

[Mike]

Shabby wrote:

> On behalf of Gemma, I'd like to point out that Brad McGee won the Commonwealth games gold medal in
> the pursuit on 175mm cranks. Good enough for you?
>
> When you are going fast you are perpendicular to the track anyway.

good point. I stand corrected.

--
make nospam into oz to reply.

 

[Mike]

Jose Rizal wrote:

> In simple terms, next time you ride a bicycle, try to see if you can apply a *constant* maximum
> force within each revolution of the crank.

<sigh> Thankyou for the lecture in the bleedin' obvious.

I think you are running with a wild misinterpretation of the original idea.

Lets try again: "The tests might have been better if lower cadence was used with longer cranks,
since I suspect optimal cadence varies with crank length. Instead of keeping the same cadence in all
trials, choose a cadence to give the same average pedal velocity. Better yet, try both, to get a
fairer comparison."

Now Jose, why choose an interpretation of "constant velocity" that isnt useful? You just love
arguing over nothing?

--
make nospam into oz to reply.

 

[Gemma Kernich]

"Mike" <[email protected]> wrote in message
news:[email protected]...
> Gemma, how about finding someone to try the 175mm cranks on a track bike? Be sure to stand by with
> a camera to document the results, and post here!

Actually, I believe some people (like Brad McGee and the like) use 175mm for pursuits - in his WC
win for example. He's probably going fast enough into the first corner not to clip a pedal though!
There was an article about him and why he chose that crank length in Ride magazine a couple of
issues ago... Gemma

 

[Jose Rizal]

Mike:

> Jose Rizal wrote:
>
> > In simple terms, next time you ride a bicycle, try to see if you can apply a *constant* maximum
> > force within each revolution of the crank.
>
> <sigh> Thankyou for the lecture in the bleedin' obvious.

Which you don't seem to grasp too well at all.

> I think you are running with a wild misinterpretation of the original idea.
>
> Lets try again: "The tests might have been better if lower cadence was used with longer cranks,
> since I suspect optimal cadence varies with crank length. Instead of keeping the same cadence in
> all trials, choose a cadence to give the same average pedal velocity. Better yet, try both, to get
> a fairer comparison."

How vapidly pedomorphic. How about you quote from what you actually wrote, rather than what you're
now trying to re-write?

From your post, 2003-04-16 20:45:31 PST

"In hindsight, you could probably pick a few faults. In particular, I think it was a mistake to use
a constant 90rpm cadence, because shorter cranks should allow a higher cadence. It would be better
to use constant pedal speed."

Constant pedal speed means constant speed of the pedal as it travels in a circular motion. This
means constant *angular* velocity of the cranks. Denying this fact, then backtracking to make it
look like you said otherwise only makes you look foolish.

> Now Jose, why choose an interpretation of "constant velocity" that isnt useful?

Now Mike, if by "useful" you mean wrong, then you are right. It doesn't, so you're not.

> You just love arguing over nothing?

It's good to see at least that your poor understanding of physics makes you dismiss your erroneous
statements as "nothing".