Slipping chainring

[Ian Jackson]

My chain has started to slip on the big chainring. It's some kind of
Shimano thing. I have replaced the chain and cassette a few times
when they seemed to slip, but never the big chainring which I'm in the
habit of using it a lot.

Is it likely that I simply need to replace the big chainring then ?
Is this a simple job ? It looks fairly simple.

--
Ian Jackson personal email: <ijac...@chiark.greenend.org.uk>
These opinions are my own. http://www.chiark.greenend.org.uk/~ijackson/
PGP2 key 1024R/0x23f5addb, fingerprint 5906F687 BD03ACAD 0D8E602E FCF37657

[Simon Mason]

On Apr 3, 4:53 pm, Ian Jackson <ijack...@chiark.greenend.org.uk>
wrote:

> My chain has started to slip on the big chainring.  It's some kind of
> Shimano thing.  I have replaced the chain and cassette a few times
> when they seemed to slip, but never the big chainring which I'm in the
> habit of using it a lot.
>
> Is it likely that I simply need to replace the big chainring then ?
> Is this a simple job ?  It looks fairly simple.
>
> --

> Ian Jackson                  personal email: <ijack...@chiark.greenend.org.uk>

> These opinions are my own.        http://www.chiark.greenend.org.uk/~ijackson/
> PGP2 key 1024R/0x23f5addb,     fingerprint 5906F687 BD03ACAD 0D8E602E FCF37657

I've done several, but I had to buy a Chainring Nut Wrench to remove
the nuts - you need an Allen key as well.

http://goo.gl/A8Sx9

Here is how it is done at 1:25m

http://www.youtube.com/watch?v=ItB_Q8LpJ8g

--
Simon Mason

[Alan Braggins]

In article <5kx*4g...@news.chiark.greenend.org.uk>, Ian Jackson wrote:
>My chain has started to slip on the big chainring. It's some kind of
>Shimano thing. I have replaced the chain and cassette a few times
>when they seemed to slip, but never the big chainring which I'm in the
>habit of using it a lot.
>
>Is it likely that I simply need to replace the big chainring then ?
>Is this a simple job ? It looks fairly simple.

Yes, and yes. (Assuming it's a replaceable chainring, anyway.
If it was a cheap crank with the chainrings riveted on, you would
need to replace the whole thing.)

_Ideally_ you want a special tool for the chainring nuts, but using
plain screwdriver in a notch isn't that fiddly, and works if they aren't
too badly corroded together. Or grip it with a Mole wrench, which will
chew it up a bit.
http://www.chainreactioncycles.com/Models.aspx?ModelID=14305
http://www.parktool.com/product/chainring-nut-wrench-cnw-2
http://www.wiggle.co.uk/lifeline-chainring-nut-tool/

(Worst case is drill it out, at which point it's not simple, but that's
unlikely: http://www.thorncycles.co.uk/forums/index.php?topic=3904.0 )

[Tosspot]

On 03/04/13 16:53, Ian Jackson wrote:
> My chain has started to slip on the big chainring. It's some kind of
> Shimano thing. I have replaced the chain and cassette a few times
> when they seemed to slip, but never the big chainring which I'm in the
> habit of using it a lot.
>
> Is it likely that I simply need to replace the big chainring then ?
> Is this a simple job ? It looks fairly simple.

Very easy, sometimes one of these

http://www.wiggle.co.uk/shimano-chainring-peg-spanner/

is needed to stop the bolts rotating. Be aware that the number of arms
and the BCD vary a bit, so make sure you're ordering like for like!

http://sheldonbrown.com/harris/chainrings.html
http://sheldonbrown.com/cribsheet-bcd.html

Other than that, allow 1/2 hour for the whole job.

[thirty-six]

On Apr 3, 4:53 pm, Ian Jackson <ijack...@chiark.greenend.org.uk>
wrote:

> My chain has started to slip on the big chainring.  It's some kind of
> Shimano thing.  I have replaced the chain and cassette a few times
> when they seemed to slip, but never the big chainring which I'm in the
> habit of using it a lot.
>
> Is it likely that I simply need to replace the big chainring then ?
> Is this a simple job ?  It looks fairly simple.
>

It might be a simple job, but you should consider firstly that you are
unable to keep your feet located stationary relative to the pedals.
It's a good time to start pedalling lighter and adjust your postion as
best you can to pedal effectively with what you currently have. The
slipping chain will remind you to pedal lighter. If you can't find a
more effective position, maybe you should consider a new, shorter
crankset, perhaps with more appropriate gears.

[David Damerell]

Quoting thirty-six <thirt...@live.co.uk>:
>On Apr 3, 4:53 pm, Ian Jackson <ijack...@chiark.greenend.org.uk>

>>My chain has started to slip on the big chainring.

>It might be a simple job, but you should consider firstly that you are
>unable to keep your feet located stationary relative to the pedals.

... because a change of pedals will cause the chainring teeth to grow
back?

>slipping chain will remind you to pedal lighter. If you can't find a
>more effective position, maybe you should consider a new, shorter
>crankset, perhaps with more appropriate gears.

Of course at a given cadence shorter cranks mean you have to push harder.
--
David Damerell <dame...@chiark.greenend.org.uk>
If we aren't perfectly synchronised this corncob will explode!
Today is Second Potmos, April.
Tomorrow will be Second Teleute, April.

[- .. -- Tim .-.]

On 03/04/2013 16:53, Ian Jackson wrote:
> My chain has started to slip on the big chainring. It's some kind of
> Shimano thing. I have replaced the chain and cassette a few times
> when they seemed to slip, but never the big chainring which I'm in the
> habit of using it a lot.
>
> Is it likely that I simply need to replace the big chainring then ?
> Is this a simple job ? It looks fairly simple.
>

Tip: With some chainrings you can take the chainring off and fit it the
other way around, so that the wear is transferred to the other edge of
each tooth. That gets a few more miles out of it.

Tim.

[Paul Luton]

I have undone more chainrings than I care to remember without needing a
tool for the nuts. A good jerk with the allen key on the bolt and
friction does the job. (of course next time there will be a problem )
When assembling grease the bolt but not the nut.

Paul

[Alan Braggins]

Possible, but less likely to apply to chainrings intended for use with a
front derailleur than to those intended to be used alone; a "big chainring"
is likely to be handed: http://sheldonbrown.com/gloss_p.html#pins

[Matthew Vernon]

"- .. -- Tim .-." <timr...@hotmail.co.uk> writes:

> Tip: With some chainrings you can take the chainring off and fit it
> the other way around, so that the wear is transferred to the other
> edge of each tooth. That gets a few more miles out of it.

Are they expensive enough that the time+hassle is worth it?

Matthew

--
`O'-----0 `O'---. `O'---. `O'---.
\___| | \___|0-/ \___|/ \___|
| | /\ | | \ | |\ | |
The Dangers of modern veterinary life

[- .. -- Tim .-.]

On 05/04/2013 14:48, Matthew Vernon wrote:
> "- .. -- Tim .-." <timr...@hotmail.co.uk> writes:
>
>> Tip: With some chainrings you can take the chainring off and fit it
>> the other way around, so that the wear is transferred to the other
>> edge of each tooth. That gets a few more miles out of it.
>
> Are they expensive enough that the time+hassle is worth it?
>
> Matthew
>

The one I saw (can't remember where) was easy to reverse, a matter of
half a dozen screws, so may be worthwhile if waiting for a new one to
arrive. I would imagine the extra miles gained might almost double the
life of the thing, and if it does, then yes, worth doing even if a new
one is only a tenner or so.

Tim.

[David Damerell]

Quoting Matthew Vernon <mat...@debian.org>:
>"- .. -- Tim .-." <timr...@hotmail.co.uk> writes:
>>Tip: With some chainrings you can take the chainring off and fit it
>>the other way around, so that the wear is transferred to the other
>>edge of each tooth. That gets a few more miles out of it.
>Are they expensive enough that the time+hassle is worth it?

Well, you are basically doing exactly what you'd be doing with a new
chainring.

If you really want to save time and hassle, buy steel chainrings.
--
David Damerell <dame...@chiark.greenend.org.uk>
Clown shoes. I hope that doesn't bother you.
Today is Second Teleute, April.
Tomorrow will be Second Oneiros, April.

[thirty-six]

On 4 Apr, 18:31, David Damerell <damer...@chiark.greenend.org.uk>
wrote:

> Quoting  thirty-six  <thirty-...@live.co.uk>:
>
> >On Apr 3, 4:53 pm, Ian Jackson <ijack...@chiark.greenend.org.uk>
> >>My chain has started to slip on the big chainring.
> >It might be a simple job, but you should consider firstly that you are
> >unable to keep your feet located stationary relative to the pedals.
>
> ... because a change of pedals will cause the chainring teeth to grow
> back?

because it represents a good time economically to consider crank
length. If there is difficulty generating much power by spinning, the
cranks are likely too long. It's cheaper to replace the the unit than
to buy a chainring, go though the bother and then changing cranks.
If there is a set of kid's cranks available, I recommend they be tried
first.

>
> >slipping chain will remind you to pedal lighter.  If you can't find a
> >more effective position, maybe you should consider a new, shorter
> >crankset, perhaps with more appropriate gears.
>
> Of course at a given cadence shorter cranks mean you have to push harder.

My experience shows that not to be the case. It's easier for me to
use cranks shorter than 170mm. I generate power through rotational
effort and key to this has been to STOP pushing. Turn the cranks,
it's that simple. If it's not easy, the cranks are likely too long
for the rider.

[thirty-six]

On 5 Apr, 18:22, David Damerell <damer...@chiark.greenend.org.uk>
wrote:
> Quoting  Matthew Vernon  <matt...@debian.org>:

>
> >"- .. -- Tim .-." <timrea...@hotmail.co.uk> writes:
> >>Tip:  With some chainrings you can take the chainring off and fit it
> >>the other way around, so that the wear is transferred to the other
> >>edge of each tooth.  That gets a few more miles out of it.
> >Are they expensive enough that the time+hassle is worth it?
>
> Well, you are basically doing exactly what you'd be doing with a new
> chainring.
>
> If you really want to save time and hassle, buy steel chainrings.

Not necessary when using molybdenum disulphide as a chain lubricant.

[David Damerell]

Quoting thirty-six <thirt...@live.co.uk>:
>On 4 Apr, 18:31, David Damerell <damer...@chiark.greenend.org.uk>

>>Of course at a given cadence shorter cranks mean you have to push harder.
>My experience shows that not to be the case.

Work is force times distance; you are mistaken.
--
David Damerell <dame...@chiark.greenend.org.uk>
And now, a seemingly inexplicable shot of a passing train.
Today is Second Aponoia, April.
Tomorrow will be Second Epithumia, April - a weekend.

[thirty-six]

On Apr 8, 6:25 pm, David Damerell <damer...@chiark.greenend.org.uk>
wrote:

> Quoting  thirty-six  <thirty-...@live.co.uk>:
>
> >On 4 Apr, 18:31, David Damerell <damer...@chiark.greenend.org.uk>
> >>Of course at a given cadence shorter cranks mean you have to push harder.
> >My experience shows that not  to be the case.
>
> Work is force times distance; you are mistaken.

Doesn't make me push harder. Pedal smoother, yes.

[nm...@cam.ac.uk]

In article <de4bddd6-30ff-421c...@a6g2000vbm.googlegroups.com>,

thirty-six <thirt...@live.co.uk> wrote:
>On Apr 8, 6:25 pm, David Damerell <damer...@chiark.greenend.org.uk>
>wrote:
>>

>> >>Of course at a given cadence shorter cranks mean you have to push harder.
>> >
>> >My experience shows that not  to be the case.
>>
>> Work is force times distance; you are mistaken.
>
>Doesn't make me push harder. Pedal smoother, yes.

Then your pedalling movement on larger cranks must be incredibly
inefficient. That's probably the case, given the difficulties
you claim to have with a natural walking cadence.


Regards,
Nick Maclaren.

[Phil Cook]

Ye cannae change the laws of physics!

To get the same work out of a shorter lever you have to push harder.
--
Phil Cook

[kimble]

On 09/04/13 12:00, Phil Cook wrote:
>>>> On 4 Apr, 18:31, David Damerell <damer...@chiark.greenend.org.uk>
>>>>> Of course at a given cadence shorter cranks mean you have to push
>>>>> harder.
>>>> My experience shows that not to be the case.
>>>
>>> Work is force times distance; you are mistaken.
>>
>> Doesn't make me push harder. Pedal smoother, yes.
>
> Ye cannae change the laws of physics!
>
> To get the same work out of a shorter lever you have to push harder.

Or push it further. It seems entirely plausible that a 'too long' crank
will reduce the efficiency of a given set of legs, to the point where
reducing the crank length enables the rider to push for more of the
pedal stroke (or pedal at a higher cadence) and be able to do more work
that way.


Kim.
--

[nm...@cam.ac.uk]

In article <asia5h...@mid.individual.net>,

Phil Cook <ph...@p-t-cook.freeserve.co.uk> wrote:
>On 09/04/2013 11:19, thirty-six wrote:
>> On Apr 8, 6:25 pm, David Damerell <damer...@chiark.greenend.org.uk>
>> wrote:
>>>
>>>>> Of course at a given cadence shorter cranks mean you have to push harder.
>>>>
>>>> My experience shows that not to be the case.
>>>
>>> Work is force times distance; you are mistaken.
>>
>> Doesn't make me push harder. Pedal smoother, yes.
>
>Ye cannae change the laws of physics!

Physics is so limiting! Try pataphysics :-)


Regards,
Nick Maclaren.

[Alan Braggins]

In article <9ffd3a-...@willow.ductilebiscuit.net>, kimble wrote:
>On 09/04/13 12:00, Phil Cook wrote:
>>>>> On 4 Apr, 18:31, David Damerell <damer...@chiark.greenend.org.uk>
>>>>>> Of course at a given cadence shorter cranks mean you have to push

^^^^^^^^^^^^^^^^^^

>>>>>> harder.
>>>>> My experience shows that not to be the case.
>>>>
>>>> Work is force times distance; you are mistaken.
>>>
>>> Doesn't make me push harder. Pedal smoother, yes.
>>
>> Ye cannae change the laws of physics!
>> To get the same work out of a shorter lever you have to push harder.
>
>Or push it further.

If you push a shorter crank at the same cadence, it doesn't travel as far.

> It seems entirely plausible that a 'too long' crank
>will reduce the efficiency of a given set of legs, to the point where
>reducing the crank length enables the rider to push for more of the
>pedal stroke (or pedal at a higher cadence) and be able to do more work
>that way.

But that doesn't change the laws of physics. If there is a significant
part of the stroke where you couldn't push effectively with long cranks
and you can with short cranks, then with the short cranks you are pushing
harder for that part of the stroke.

Possibly that's what thirty-six means by pedalling smoother not harder;
he may be pedalling harder on average over the stroke without having
increased the peak force.

[- .. -- Tim .-.]

AIUI the technique of 'ankling' is all important. Similar to turning a
handle with your hand, you don't turn it by just thrusting straight
downwards. Thus trying to apply a smooth continuous turning pressure to
the pedals is the key to efficiency, and attaining a high rotational
speed also enables less force to be applied, by using a lower gear.

Tim.

[nm...@cam.ac.uk]

In article <yvidnTnVuf5QqvnM...@bt.com>,

- .. -- Tim .-. <timr...@hotmail.co.uk> wrote:
>
>AIUI the technique of 'ankling' is all important. Similar to turning a
>handle with your hand, you don't turn it by just thrusting straight
>downwards. Thus trying to apply a smooth continuous turning pressure to
>the pedals is the key to efficiency, and attaining a high rotational
>speed also enables less force to be applied, by using a lower gear.

While I agree that ankling is important, it is more because it
reduces the effective crank length as far as it affects the knee
angle, while using the length to keep the force down.

However, your second point is dubious, though it is a widespread
article of faith. The point is that, for a typical fit but not
athletic rider, the force is only about 10-15% of that needed when
walking up a steepish (say, 33+%) hill with a full, camping pack.
And that rarely causes trouble - it's downhill that does.

Also, problem is as much in changing direction of the knee joint
as in actually pushing, and (because of the time^2 term), those
forces are pro rata to cadence, not inversely proportional to
it. That is why a lot of people find lower cadences are easier
on their knees, even at constant speeds.

Part of the trouble here is that there has been VERY little actual
research into the ergonomics of bicycles, except for the extreme
and self-selected group of cyclists who can deliver 250+ watts
in a UCI position.


Regards,
Nick Maclaren.

[David Damerell]

Quoting - .. -- Tim .-. <timr...@hotmail.co.uk>:
>AIUI the technique of 'ankling' is all important. Similar to turning a
>handle with your hand, you don't turn it by just thrusting straight
>downwards. Thus trying to apply a smooth continuous turning pressure to
>the pedals is the key to efficiency, and attaining a high rotational
>speed also enables less force to be applied, by using a lower gear.

This is all very well (although I tend to raise an eyebrow at the blithe
assumption made by some high-cadence fans that doing more duty cycles at
lower force per cycle is better for the knees; I don't know, but neither
do they), but these factors are basically orthogonal to crank length. If
all other factors are equal shorter cranks mean higher force. Kim's
suggestion that one can ankle more on shorter cranks is interesting, but
Ian is not one of those very short people where 170mm cranks look a bit
disproportionate.
--
David Damerell <dame...@chiark.greenend.org.uk> Distortion Field!
Today is Second Epithumia, April - a weekend.
Tomorrow will be Second Olethros, April - a weekend.

[thirty-six]

On Apr 9, 5:39 pm, n...@cam.ac.uk wrote:
> In article <yvidnTnVuf5QqvnMnZ2dnUVZ7sCdn...@bt.com>,

> - .. -- Tim .-. <timrea...@hotmail.co.uk> wrote:
>
>
>
> >AIUI the technique of 'ankling' is all important.  Similar to turning a
> >handle with your hand, you don't turn it by just thrusting straight
> >downwards.  Thus trying to apply a smooth continuous turning pressure to
> >the pedals is the key to efficiency, and attaining a high rotational
> >speed also enables less force to be applied, by using a lower gear.
>
> While I agree that ankling is important,

It's not, yet it may assist when the crank length is excessive and it
may reduce any tendency to fatigue in periods of high pedal force, it
is not in itself beneficial to pedalling efficiency.

> it is more because it
> reduces the effective crank length as far as it affects the knee
> angle, while using the length to keep the force down.

The foot still has to travel the same distance front to back however
the ankle is bent. There is no "effective length", the crank length
does not change. When my feet go (too) far back either due to saddle
position or long cranks it is difficult for me to make the transtions
between the horizontal phases and the lifting phase.

>
> However, your second point is dubious, though it is a widespread
> article of faith.  The point is that, for a typical fit but not
> athletic rider, the force is only about 10-15% of that needed when
> walking up a steepish (say, 33+%) hill with a full, camping pack.
> And that rarely causes trouble - it's downhill that does.
>
> Also, problem is as much in changing direction of the knee joint
> as in actually pushing, and (because of the time^2 term), those
> forces are pro rata to cadence, not inversely proportional to
> it.  That is why a lot of people find lower cadences are easier
> on their knees, even at constant speeds.

If you are not comfortable with 85rpm+ after a few weeks riding then
your fit is wrong or you have a metabolic or neurological failure.

>
> Part of the trouble here is that there has been VERY little actual
> research into the ergonomics of bicycles, except for the extreme
> and self-selected group of cyclists who can deliver 250+ watts
> in a UCI position.

When I was riding at 8mph with all my worth, a 2mm deviation from
position would have had me on the ground. That's, almost, the same
position I could sprint at over 50mph not 12 months before. Hands in
hooks for sprinting.


That 50mph sprint, from 20mph in about 10 seconds, is probably in
excess of 2kW and the bike (although a racing bike) was (almost) set
up for day touring, not racing. There's little difference (s
everywhere), the day tourist usually uses a wider "square" bar with a
position which is optimised for climbing and easy riding on the tops
and hoods, has gears between 35" and 85" on a sturdy rear wheel, has
one decent bag and a head that keeps him out of trouble. I know how
to get the best from a bike in racing and touring, I'm learning what's
best for my body. That planar knee motion is best was determined by
me, as a tourist, not a racer. I use(d) such a position because it
left me with least fatigue, not because i could attain the greatest
speed on the road. Protection from injury, minimising fatigue and
elimination of and avoiding illness are my goals.

[nm...@cam.ac.uk]

In article <8nl9m8db7074dro1p...@4ax.com>,
Phil W Lee <ph...@lee-family.me.uk> wrote:
>David Damerell <dame...@chiark.greenend.org.uk> considered Tue, 09
>Apr 2013 18:42:28 +0100 the perfect time to write:
>
>All other factors won't be equal though - people with shorter cranks
>usually fit lower gearing and spin faster.
>Check it using Sheldon's gain ratios (which give a complete picture of
>actual gearing) rather than simply using gear inches, which don't
>include the crank length.

Yes. All of the factors interact, and it is impossible to assign
cause and effect to individual ones.

>> Kim's
>>suggestion that one can ankle more on shorter cranks is interesting, but
>>Ian is not one of those very short people where 170mm cranks look a bit
>>disproportionate.

And my experience is that it is wrong, anyway. On shorter cranks,
with even a slightly higher cadence, I don't get TIME to ankle!
Spinning is an unnatural movement and, as a result, needs hundreds
of hours of practice to develop as a reflex. All of the leg
movements that have evolved naturally are reciprocating.

>I reckon 170s look disproportionate on most people, and 165 about
>right. Crank lengths have been set largely by fashion dictated by the
>desire to have a bike like <insert cycling hero here>'s.
>If we were actually suited to those measurements, we'd all be
>potential <insert pro cycling event of choice here> winners - and we
>(or the overwhelming majority of us) patently aren't.

Well, yes, they have, but you have missed one critical point.
Cycling positions and movements have also been set the same way
(in the UK), and the traditional upright ones have been replaced
by more-or-less UCI-derived ones or by a half-way house. My
experiments (using myself as the subject) are that the optimum
crank length varies CONSIDERABLY with position, and I need much
shorter ones even in a half-crouch. 170 mm was the traditional
length for taller riders, who were shorter then than now. I am
about the same height as Ian, and would be best off with 175 or
180 mm. But he doesn't ride wholly upright.


Regards,
Nick Maclaren.

[Ian Jackson]

In article <8nl9m8db7074dro1p...@4ax.com>,
Phil W Lee <ph...@lee-family.me.uk> wrote:

>Looking at a non athletic rider struggle with 175mm cranks is like
>watching an advanced arthritis sufferer climb stairs two at a time.

So, err, I may be stretching your analogy beyond breaking point here,
but if I almost always climb stairs two at a time, should I therefore
be expected to prefer longer cranks ?

--
Ian Jackson personal email: <ijac...@chiark.greenend.org.uk>
These opinions are my own. http://www.chiark.greenend.org.uk/~ijackson/
PGP2 key 1024R/0x23f5addb, fingerprint 5906F687 BD03ACAD 0D8E602E FCF37657

[nm...@cam.ac.uk]

In article <tQw*fe...@news.chiark.greenend.org.uk>,

Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>In article <8nl9m8db7074dro1p...@4ax.com>,
>Phil W Lee <ph...@lee-family.me.uk> wrote:
>>Looking at a non athletic rider struggle with 175mm cranks is like
>>watching an advanced arthritis sufferer climb stairs two at a time.
>
>So, err, I may be stretching your analogy beyond breaking point here,
>but if I almost always climb stairs two at a time, should I therefore
>be expected to prefer longer cranks ?

In my view, yes. I do it mainly to maintain my quadriceps, now
I dare not commute on a bicycle. That's the same amount of knee
bend as (say) a 170 mm crank, and you are pushing your whole
weight, not a fraction of it.


Regards,
Nick Maclaren.

[Matthew Vernon]

ijac...@chiark.greenend.org.uk (Ian Jackson) writes:

> In article <8nl9m8db7074dro1p...@4ax.com>,
> Phil W Lee <ph...@lee-family.me.uk> wrote:
>>Looking at a non athletic rider struggle with 175mm cranks is like
>>watching an advanced arthritis sufferer climb stairs two at a time.
>
> So, err, I may be stretching your analogy beyond breaking point here,
> but if I almost always climb stairs two at a time, should I therefore
> be expected to prefer longer cranks ?

I prefer extended cranks, which is why I don't use a killfile.

Matthew
I'll get my coat

[David Damerell]

Quoting thirty-six <thirt...@live.co.uk>:
>That 50mph sprint, from 20mph in about 10 seconds, is probably in
>excess of 2kW

Certainly. 100kg of bike+rider moving at 20mph has about 4kJ of kinetic
energy. At 50mph, about 25kJ. So to do that in ten seconds you'd have to
put out a little over 2kW... if you were riding in a vacuum (and also
neglecting rolling resistance). With air resistance it is of course
completely impossible.

--
David Damerell <dame...@chiark.greenend.org.uk>
Clown shoes. I hope that doesn't bother you.

Today is Second Olethros, April - a weekend.
Tomorrow will be Monday, April.

[David Damerell]

Quoting Phil W Lee <ph...@lee-family.me.uk>:
>David Damerell <dame...@chiark.greenend.org.uk> considered Tue, 09

>>If all other factors are equal shorter cranks mean higher force.

>All other factors won't be equal though - people with shorter cranks
>usually fit lower gearing and spin faster.

Well, yeah - not least because it will reduce the pedalling force again.

All I'm saying is that if you feel pedalling force is too high, reducing
crank length is exactly the wrong move.

[thirty-six]

On Apr 10, 3:55�pm, ijack...@chiark.greenend.org.uk (Ian Jackson)
wrote:
> In article <8nl9m8db7074dro1paismv7urjp3nq5...@4ax.com>,

> Phil W Lee �<p...@lee-family.me.uk> wrote:
>
> >Looking at a non athletic rider struggle with 175mm cranks is like
> >watching an advanced arthritis sufferer climb stairs two at a time.
>
> So, err, I may be stretching your analogy beyond breaking point here,
> but if I almost always climb stairs two at a time, should I therefore
> be expected to prefer longer cranks ?
>

You may, for the same period. How many minutes or hours do you climb
two at a time? After 6 hours of continuous climbing, are you still
going two steps at a time? What about after 30 minutes? Do you
believe that cranks should vary in length depending on how you feel
from one minute to the next?

Where is this staircase to the clouds?

[thirty-six]

On Apr 10, 4:05�pm, n...@cam.ac.uk wrote:
> In article <tQw*fe...@news.chiark.greenend.org.uk>,
>

> Ian Jackson <ijack...@chiark.greenend.org.uk> wrote:
> >In article <8nl9m8db7074dro1paismv7urjp3nq5...@4ax.com>,

> >Phil W Lee �<p...@lee-family.me.uk> wrote:
> >>Looking at a non athletic rider struggle with 175mm cranks is like
> >>watching an advanced arthritis sufferer climb stairs two at a time.
>
> >So, err, I may be stretching your analogy beyond breaking point here,
> >but if I almost always climb stairs two at a time, should I therefore
> >be expected to prefer longer cranks ?
>
> In my view, yes. �I do it mainly to maintain my quadriceps, now

wrong way around. It's coming down, or going up backwads which
effectively targets one's quadriceps. Going two steps and more
upwards generates a fat arse. For most people it takes an abnormal
range of movement and is certainly best commonly avoided if one wishes
to become most proficient at cycling.

[Ian Jackson]

In article <5jfbm8p0n6t0v7prl...@4ax.com>,

Phil W Lee <ph...@lee-family.me.uk> wrote:

>ijac...@chiark.greenend.org.uk (Ian Jackson) considered Wed, 10 Apr

>2013 15:55:15 +0100 the perfect time to write:
>>So, err, I may be stretching your analogy beyond breaking point here,
>>but if I almost always climb stairs two at a time, should I therefore
>>be expected to prefer longer cranks ?
>

>That is entirely possible.
>What is your climbing cadence? :-D

Dunno. Depends on the grade I guess :-). (I've just been to the
climbing wall.)

More seriously, I don't know - I guess a fairly normal
running-up-stairs cadence.

[thirty-six]

On 10 Apr, 18:36, David Damerell <damer...@chiark.greenend.org.uk>
wrote:

> Quoting �thirty-six �<thirty-...@live.co.uk>:
>
> >That 50mph sprint, from 20mph in about 10 seconds, is probably in
> >excess of 2kW
>
> Certainly. 100kg of bike+rider

maybe 83kg.

> moving at 20mph has about 4kJ of kinetic
> energy. At 50mph,

perhaps it was a 42 ring (with 16t rear) not a 48, but the final speed
was then still 48mph at 238rpm. It was certainly the 16 sprocket.

> about 25kJ. So to do that in ten seconds

some of the first "sprints" I did were over 20 seconds duing
acceleration and I was getting whacked without able to maintain speed
once I'd peaked so I paid attention to acceleration speed. Ten
seconds acceleration was what I aimed for and got it.

> you'd have to
> put out a little over 2kW... if you were riding in a vacuum (and also
> neglecting rolling resistance). With air resistance it is of course
> completely impossible.

Track sprinters do that. The top riders are not hampered by notions
of failing.

[David Damerell]

Quoting thirty-six <thirt...@live.co.uk>:
>On 10 Apr, 18:36, David Damerell <damer...@chiark.greenend.org.uk>

>>Quoting �thirty-six �<thirty-...@live.co.uk>:
>>>That 50mph sprint, from 20mph in about 10 seconds, is probably in
>>>excess of 2kW
>>Certainly. 100kg of bike+rider
>maybe 83kg.

Makes very little difference; still impossible.

>>you'd have to
>>put out a little over 2kW... if you were riding in a vacuum (and also
>>neglecting rolling resistance). With air resistance it is of course
>>completely impossible.
>Track sprinters do that. The top riders are not hampered by notions
>of failing.

No, they don't. Let's take a look at
http://www.srm.de/es/srm-in-action/competition-with-srm/bahn/465-sprint-maenner

This is a trace from a world-class rider in a 200m sprint. Peak speed is
45mph - and needless to say, he's going rather faster than 20mph ten
seconds beforehand. Peak power - absolute peak, hit for a moment, not
sustained for ten seconds - is just under 1900W. Average power is just
under 1200W.

The top riders are hampered by physics; and to go from 20mph to 50mph in
ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
vacuum. One rarely rides in a vacuum.
--
David Damerell <dame...@chiark.greenend.org.uk> Oil is for sissies
Today is Monday, April.
Tomorrow will be Tuesday, April.

[thirty-six]

On 11 Apr, 16:31, David Damerell <damer...@chiark.greenend.org.uk>
wrote:

> Quoting �thirty-six �<thirty-...@live.co.uk>:
>
> >On 10 Apr, 18:36, David Damerell <damer...@chiark.greenend.org.uk>
> >>Quoting �thirty-six �<thirty-...@live.co.uk>:
> >>>That 50mph sprint, from 20mph in about 10 seconds, is probably in
> >>>excess of 2kW
> >>Certainly. 100kg of bike+rider
> >maybe 83kg.
>
> Makes very little difference; still impossible.
>
> >>you'd have to
> >>put out a little over 2kW... if you were riding in a vacuum (and also
> >>neglecting rolling resistance). With air resistance it is of course
> >>completely impossible.
> >Track sprinters do that. �The top riders are not hampered by notions
> >of failing.
>

> No, they don't. Let's take a look athttp://www.srm.de/es/srm-in-action/competition-with-srm/bahn/465-spri...

>
> This is a trace from a world-class rider in a 200m sprint.

He wasn't world class on that day.

> Peak speed is
> 45mph - and needless to say, he's going rather faster than 20mph ten
> seconds beforehand. Peak power - absolute peak, hit for a moment, not
> sustained for ten seconds - is just under 1900W. Average power is just
> under 1200W.

2300W has been measured, probably a fully developed man of 6' 2'".
while I have not attained such stature, I do have nearly the same
torso and wise enough to use shorter cranks during the period my legs
remain underdeveloped.

>
> The top riders are hampered by physics; and to go from 20mph to 50mph in
> ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
> vacuum. One rarely rides in a vacuum.

I did make 48mph repeatedly and the last of those sprints were
triggered when my cadence dipped to 99, a speed of 20.3mph (I was
cruising at around 111) They were made in around, not by much more,
ten seconds (analogue watch and cadence meter on handlebar).to attain
between 230 and 238rpm at 48mph or so. I don't really care what
wattage it was, I had also soaked up a couple of hours of bright sun,
6 or so lesser sprints, and deep controlled breathing with a little
sea air (but no sea paddling) before each of those fast sprints.

These were the best cycling days that I possibly ever had, "the wind
was at my back and turned every corner with me". They were only a
few days and I have the will to regain them, possibly take me a couple
of years to cleanse my body and supposedly another 7 to fully
regenerate.

[The Luggage]

On Apr 11, 4:31�pm, David Damerell <damer...@chiark.greenend.org.uk>
wrote:

> Quoting �thirty-six �<thirty-...@live.co.uk>:
>
> >On 10 Apr, 18:36, David Damerell <damer...@chiark.greenend.org.uk>
> >>Quoting �thirty-six �<thirty-...@live.co.uk>:
> >>>That 50mph sprint, from 20mph in about 10 seconds, is probably in
> >>>excess of 2kW
> >>Certainly. 100kg of bike+rider
> >maybe 83kg.
>
> Makes very little difference; still impossible.
>
> >>you'd have to
> >>put out a little over 2kW... if you were riding in a vacuum (and also
> >>neglecting rolling resistance). With air resistance it is of course
> >>completely impossible.
> >Track sprinters do that. �The top riders are not hampered by notions
> >of failing.
>

> No, they don't. Let's take a look athttp://www.srm.de/es/srm-in-action/competition-with-srm/bahn/465-spri...

>
> This is a trace from a world-class rider in a 200m sprint. Peak speed is
> 45mph - and needless to say, he's going rather faster than 20mph ten
> seconds beforehand. Peak power - absolute peak, hit for a moment, not
> sustained for ten seconds - is just under 1900W. Average power is just
> under 1200W.
>
> The top riders are hampered by physics; and to go from 20mph to 50mph in
> ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
> vacuum. One rarely rides in a vacuum.

So let's do the calculation...

power = 0.5 * v^3 A Cd.
For a sprinter, we can take Cd x A as 0.25 (http://
www.cyclingpowerlab.com/CyclingAerodynamics.aspx)
so at 50 mph (= 22.3 m/s), power required to overcome aerodynamic drag
= 1386 W.

This is in addition to the 2090W for the acceleration.

Somehow I don't believe anyone can achieve nearly 3.5 kW, let alone
sustain it for the last few seconds of the sprint.

TL

[nm...@cam.ac.uk]

In article <ZEo*gu...@news.chiark.greenend.org.uk>,

David Damerell <dame...@chiark.greenend.org.uk> wrote:
>
>The top riders are hampered by physics; and to go from 20mph to 50mph in
>ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
>vacuum. One rarely rides in a vacuum.

Well, you and I don't. "thirty-six" can answer for himself.

More seriously, I can believe that a top athlete could just achieve
that - it's what I estimate Olympic-class 100 metre sprinters get
to. However, I do not believe that anyone could achieve it except
when absolutely fresh, and then only once. Nor do I believe that
more than a small fraction of the population could achieve it, not
even if they trained flat-out for the rest of their lives.



Regards,
Nick Maclaren.

[Alan Braggins]

http://www.livestrong.com/article/443321-the-mechanical-power-used-by-a-sprinter/
agrees with you: "As of May 2011, Usain Bolt is the fastest man in the world.
With a world-record time of 9.58 seconds in the 100-meter dash, he produces
2,165 watts of power."

However, Bolt is only overcoming air resistance at the lower end of that
20mph to 50mph, which makes thirty-six either the finest athlete in the
world, or mistaken.

[David Damerell]

Quoting thirty-six <thirt...@live.co.uk>:
>On 11 Apr, 16:31, David Damerell <damer...@chiark.greenend.org.uk>

>2300W has been measured, probably a fully developed man of 6' 2'".

... so with yet more mass to accelerate and more air resistance, which
might matter if this claim were remotely possible.

> I did make 48mph repeatedly and the last of those sprints were
>triggered when my cadence dipped to 99, a speed of 20.3mph (I was
>cruising at around 111) They were made in around, not by much more,
>ten seconds

My point is simply that you must be mistaken. This is not physically
possible for a human being. You might as well tell me that you grabbed
some Moon rocks by doing stretches before reaching up.
--
David Damerell <dame...@chiark.greenend.org.uk>
And now, a seemingly inexplicable shot of a passing train.
Today is Tuesday, April.
Tomorrow will be Wednesday, April.

[thirty-six]

On 12 Apr, 16:28, n...@cam.ac.uk wrote:
> In article <ZEo*gu...@news.chiark.greenend.org.uk>,

> David Damerell �<damer...@chiark.greenend.org.uk> wrote:
>
>
>
> >The top riders are hampered by physics; and to go from 20mph to 50mph in
> >ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
> >vacuum. One rarely rides in a vacuum.
>
> Well, you and I don't. �"thirty-six" can answer for himself.
>
> More seriously, I can believe that a top athlete could just achieve
> that - it's what I estimate Olympic-class 100 metre sprinters get
> to. �However, I do not believe that anyone could achieve it except
> when absolutely fresh, and then only once.

Exactly. If I had been at the velodrome I'd have to be capable of
making near that every 15 minutes (without sun at Manchester). The
thoughts crossed my mind at the time, but illness took hold not long
after. I am now undertanding that the efforts likely sparked my
immune system into motion but i was unable to support its function
because of madically prescibed prednisolone and a lack of knowledge
about how food interacts with one's body, at that time.

> �Nor do I believe that

> more than a small fraction of the population could achieve it, not
> even if they trained flat-out for the rest of their lives.
>

As I said before, my legs are proportionally short when taking account
of my torso. I'm a bigger man inside and my shorter legs and
narrow(ish) shoulders offer less windage than your traditionally
accepted sprinter's form. I had in my early twe ties been killing
myself (along with madically prescribed tetracycline) with cycle
training for competition. I believe I had built a giant's lymphatic
capacity with enhanced network with blood and lymph vessels during
that time, but the drugs (of madical origin) stagnated my lymph. I am
now recovering (and get whacked out 3 or 4 times a day). I am still
not fit enough to have an enthusiastic ride. Even a gentle ride right
now would be too stimulating for me. It is time for me to recover and
my hope is to return to competitive cycling (when my porous bones have
recovered and other stuff) possibly in four years, but at the track
and maybe get that sprint filmed and verified. I'll be 50

[thirty-six]

On 12 Apr, 19:00, a...@chiark.greenend.org.uk (Alan Braggins) wrote:
> In article <kk95oc$3u...@needham.csi.cam.ac.uk>, n...@cam.ac.uk wrote:

> >David Damerell �<damer...@chiark.greenend.org.uk> wrote:
>
> >>The top riders are hampered by physics; and to go from 20mph to 50mph in
> >>ten seconds would need 2kW (well, 20W for each kg of bike+rider) in a
> >>vacuum. One rarely rides in a vacuum.
>
> >Well, you and I don't. �"thirty-six" can answer for himself.
>
> >More seriously, I can believe that a top athlete could just achieve
> >that - it's what I estimate Olympic-class 100 metre sprinters get
> >to. �However, I do not believe that anyone could achieve it except
> >when absolutely fresh, and then only once. �Nor do I believe that
> >more than a small fraction of the population could achieve it, not
> >even if they trained flat-out for the rest of their lives.
>

> http://www.livestrong.com/article/443321-the-mechanical-power-used-by...

> agrees with you: "As of May 2011, Usain Bolt is the fastest man in the world.
> With a world-record time of 9.58 seconds in the 100-meter dash, he produces
> 2,165 watts of power."
>
> However, Bolt is only overcoming air resistance at the lower end of that
> 20mph to 50mph, which makes thirty-six either the finest athlete in the
> world, or mistaken.

I was the fastest runner at school out of 150. Come the annual games
day, I'd get put in the long jump, triple jump and javelin (with short
legs?) I came to realise that I'd upset too many if I was running
the 100,200 and 400 and I kept qua;ifyoing for the field games so
didn't get a look in for the track. I won the long jump each year and
was 1 or 2 for the triple. Over short distances no-one could match
my pace, but a full football match could easily exhaust me. I had
the speed, not the capacity. I developed capacity on the bike but
could not maintain the power (although 10 minute power was fine) of
the others. It's only when i gave up all thought of competition
following illness, and a self assessment of "training" did my cycle
sprinting ability show.
It is possible that some genetic mutation during my early period of
illness allowed me to come back stronger , but due to the drugs-for-
life program I was unable to make recovery following that summer and
have been struggling since.

[Ian Jackson]

In article <5kx*4g...@news.chiark.greenend.org.uk>,
Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>Is it likely that I simply need to replace the big chainring then ?
>Is this a simple job ? It looks fairly simple.

I tried to get the LBS to fix this because I was lazy. This turns out
to have been a mistake because they said they weren't able to get the
parts - discontinued by Shimano apparently.

David tells me in person that this is mad and they're a readily
available item of commerce. Indeed they do seem to be. My bolt
circle diameters are 104, 104, 64mm (well actually I measured the
inter-bolt spacing as 74mm, 74mm, 45mm - there's 4 bolts in a square).
48, 36, 26 teeth. Originally fitted equipment was Shimano "M532".

But when I look online I'm confronted with a huge variety of
chainrings of various kinds. Do I care (from a compatibility) whether
they're made by Shimano or have the same "M532" model number ? There
seem to be a lot of "M510" about.

Also, they're surprisingly expensive - particular the big ring seems
to start at around L25.

[Clive George]

On 11/05/2013 01:49, Ian Jackson wrote:
> In article <5kx*4g...@news.chiark.greenend.org.uk>,
> Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>> Is it likely that I simply need to replace the big chainring then ?
>> Is this a simple job ? It looks fairly simple.
>
> I tried to get the LBS to fix this because I was lazy.

Careless :-)

> This turns out
> to have been a mistake because they said they weren't able to get the
> parts - discontinued by Shimano apparently.

It's entirely possible that the genuine parts aren't available. But that
shouldn't be a problem.

> David tells me in person that this is mad and they're a readily
> available item of commerce. Indeed they do seem to be. My bolt
> circle diameters are 104, 104, 64mm (well actually I measured the
> inter-bolt spacing as 74mm, 74mm, 45mm - there's 4 bolts in a square).
> 48, 36, 26 teeth. Originally fitted equipment was Shimano "M532".

He's right, and I think your measurements look sane.

> But when I look online I'm confronted with a huge variety of
> chainrings of various kinds. Do I care (from a compatibility) whether
> they're made by Shimano or have the same "M532" model number ? There
> seem to be a lot of "M510" about.

No. Tooth count, bolt layout are what really counts. You might care
about quality, and they will vary.

I did learn the hard way a while ago that Campag's 110mm 5-hole BCD
rings have one of the holes on a different pitch, which is annoying
(resulted in some filing...), but your 4 bolt shimano shouldn't have
anything like that going on.

> Also, they're surprisingly expensive - particular the big ring seems
> to start at around L25.

Yup. I'm always surprised how expensive chainrings have got. (and I
shouldn't be by now...)

[thirty-six]

On May 11, 3:21�am, Clive George <cl...@xxxx-x.fsnet.co.uk> wrote:
> On 11/05/2013 01:49, Ian Jackson wrote:
>
> > In article <5kx*4g...@news.chiark.greenend.org.uk>,

so how many coconuts or magoes dos tak to buy a chainring from West
coastUSa?

[Alan Braggins]

In article <GPudnQpPMMprNxDM...@brightview.co.uk>, Clive George wrote:
>On 11/05/2013 01:49, Ian Jackson wrote:
>> In article <5kx*4g...@news.chiark.greenend.org.uk>,
>> Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>>> Is it likely that I simply need to replace the big chainring then ?
>>> Is this a simple job ? It looks fairly simple.
>>
>> I tried to get the LBS to fix this because I was lazy.
>
>Careless :-)
>
>> This turns out
>> to have been a mistake because they said they weren't able to get the
>> parts - discontinued by Shimano apparently.
>
>It's entirely possible that the genuine parts aren't available. But that
>shouldn't be a problem.

Yes. "The exact replacement part isn't available, and we won't decide
what part is equivalent for you" is unhelpful but perhaps not totally
unreasonable, if explained clearly, but "can't do it, can't get the
parts" is just wrong. It's not as if you've got an obscure size on a
classic bike like these: http://hilarystone.com/CCchainrings.html
http://janheine.wordpress.com/2011/07/06/rene-herse-cranks/

Which LBS?

>> Also, they're surprisingly expensive - particular the big ring seems
>> to start at around L25.
>
>Yup. I'm always surprised how expensive chainrings have got. (and I
>shouldn't be by now...)

By the time you spend another L10 each on inner and middle, almost
worth just buying the whole crankset:
http://www.sjscycles.co.uk/shimano-deore-fc-m532-9-spd-hollowtech-ii-triple-chainset-48-36-26t-prod15390/

Or what I assume is the current equivalent, which comes with BB bearings:
http://www.chainreactioncycles.com/Models.aspx?ModelID=40496

[Ian Jackson]

In article <5kx*4g...@news.chiark.greenend.org.uk>,
Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>Is it likely that I simply need to replace the big chainring then ?
>Is this a simple job ? It looks fairly simple.

Latest installment of this saga: I came back from a trip to find the
chainrings and new chain waiting for me. Excellent.

So I set about unscrewing things. I found I couldn't take the small
chainring off without removing the cranks. And removing the cranks
didn't seem trivial. Eventually I found this:
http://www.enduroforkseals.com/sitebuildercontent/sitebuilderfiles/hollowtech2a.pdf

That looked promising except I didn't have the magic tool for removing
the crank cap thingy. Improvising didn't seem to work very well.

So I ended up using our 3D printer to print a crank cap remover tool:
http://www.chiark.greenend.org.uk/~ijackson/2013/deore-crank-remover-screenshot.png
http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=reprap-play.git;a=blob;f=deore-crank-remover.scad;hb=HEAD
http://www.chiark.greenend.org.uk/~ijackson/2013/deore-crank-remover-photo.jpg

Amazingly, once I had shaved that yak, my cheap plastic imitation
magic tool worked!

>From then on it was all quite straightforward. So the new chainrings
and chain have been bench tested and will get a short outing later to
see how well it all works.

Thanks to everyone for your help and advice!

[Ian Jackson]

In article <1oo*ik...@news.chiark.greenend.org.uk>,
Ian Jackson <ijac...@chiark.greenend.org.uk> wrote:
>From then on [fitting the new chainrings and putting back the
>cranks] it was all quite straightforward. So the new chainrings and

>chain have been bench tested and will get a short outing later to see
>how well it all works.

Badly, was the answer. The cassette was very bad worn, too. Another
few days' delay and fitting that meant my bike worked properly! For
the first time in ages. And it looks like my legs haven't atrophied
in the meantime :-).