Crank Stiffness Tests???

wrote:
Jasper Janssen writes:


The straight down version would be more-or-less the equivalent of
directly applying a load sideways on the crank face (ie, hold the
crank horizontal by the spindle and apply a load to the pedal
eyelet, since most testing machines are vertically oriented). More
less than more, because the pedal/crank eye interface contributes
significantly, and can be different between cranks. Especially so
for carbon, where there is an extra material interface designed in
the crank, and thus no "but all cranks act the same in that respect"
thing.


That won't do. You would never get a pedal eye failure from a side
load applied at that point.


Yes, I agree. I'm just sayin', that test may have been done by some
laboratories.


Since the load must be applied at the center of pressure for the
horizontal crank position to show torsional rigidity, you should
also apply the load there in the straight down position.


Center of pressure? You mean the point n cm from the pedal eye
where n corresponds to the average person pressing on the average
pedal?


Yes, the normal pressure point where the load is applied.


Simply to go for worst-case, I'd probably do it at the end of the
pedal.


There is a relationship between rotational torque and lateral bending,
both of which affect rigidity. Just the same, rigidity is not a
reasonable consideration with cranks that don't break, so I think the
whole subject is something for the weight wienies.


Apart, of course, from the ones that are gravitating to hollow
girders.


Material inside the cross section adds no significant strength
while driving the weight wienies crazy. I find amazing how much
riders spend on grams saved by these design quirks. Hollow cranks!


What is it again, $100 per oz? Ridiculous numbers indeed.


As I said, InterBike is drifting off into fashion technology that
one can discuss endlessly, like spoke patterns and rim cross sections.


I think there is a third parameter, that might be a bit harder to
test for: Chainring versus pedal versus spindle movement. You
really need to include the rings and not just the spider because
rings of equal number of teeth with a smaller spider will be, in
and of themselves, flexier (but the spider will be less flexible
and the question is whether it matters as a whole).


It doesn't matter and should not be included both for that reason
and simplicity of the test, because only the left crank need be
analyzed to give a figure of merit.


Okay, I'll agree that testing the left crank alone is much, much
easier and probably tells you as much as you need to know.


However, why does the spider/chainring stiffness not matter? It's
not a safety issue (much), admittedly, but purely on stiffness and
energy-loss-into-flexing grounds it ought to matter, surely? There
are people around who've managed to collapse spider/chainrings,
while the cranks themselves took the load.


There is no significant flex in the spider

er, jobst, remember when you were studying the fundamentals of fatigue?
remember the bit about how fatigue is the result of cyclic strain -
you know, elasic deformation? that's otherwise known as "flex". back
in the day when cranks frequently broke at the spider, that was because
the flex the crank was experiencing at the spider was causing fatigue to
propagate. no flex, no fatigue. nowadays, we still have flex, but
improved metallurgy improves fatigue life significantly.

and especially the
chainring. I rode on much flimsier CW spiders and rings in the days
of steel cranks and noticed no flex. Pedal flex is primarily in the
bicycle frame, not in cranks, crank spiders or chainrings. I think
the whole subject is off base because crank failure is the main
parameter of interest, the micro-motion of crank flex being trivial in
comparison. Just sit on your bicycle and push on one pedal. There is
significant motion but it isn't in the crank assembly.

this is amazing - you don't "notice" any flex, but aren't you the one
that always bleats about a similar effect manifesting itself in one of
your favorite phenomena, fretting?



Just the same, until such cranks have been used and have
experienced failures, this will be an unknown for some time.
Consider how long aluminum cranks have taken to become the reliable
ones we have today. There are still many aluminum cranks that are
failure prone. Shimano did not drop the Octalink for nothing, nor
did Campagnolo drop the Delta brake likewise. These were design
failures that could have been avoided by consulting the appropriate
industries where such things were understood.


I'm not so sure they could've been avoided entirely. Sure,
sometimes the bike industry reinvents the wheel, but quite a lot of
the time they're doing things that are just different enough that
knowledge from elsewhere doesn't apply.


Cranks have been made for a long time now and there is no excuse for
using the I-beam shape that is still popping up aplenty. Servo
brakes, and non linear brakes are no good in bicycles for the same
reasons they are no good on motor vehicles. Crank retaining bolts
loosening is for the same reasons as in other machinery.


F'r instance, apart from other types of racing and aerospace,
nobody's as much of a weight weenie as the bike industry. And
*nobody*, period, is as much of a weight weenie, while
simultaneously dealing with highly unpredictable loads and
incredible variances of net vehicle weight.


That is classic for the human interface because each person may use
the product in an unpredictable manner. Regardless, performance on a
bicycle is mainly the rider and when performance is less than
expected, the equipment gets the blame. Where else can we find
excuses? The bicycle doesn't talk back when getting the blame. It's
fair game.

Jobst Brandt

er, so fatigue is the user's fault? i guess it is since if they didn't
use it, it couldn't fatigue. thanks for the clarification.

Sandy wrote:
Dans le message de
oups.com,
Qui si parla Campagnolo a réfléchi, et puis a déclaré :
Sandy wrote:


Gee, Peter, I am trying to remember. I had to look it up. The
figures I quoted from Le Cycle magazine's test were far from
extraordinary. I wonder where your tests were published, so I could
get a look at them. You didn't make that statement up, by any
chance ???

If they used forces like those exerted by the average, 45 yr old
cyclist, then the results would have been inconclusive and not able
to be used by the marketeers.

So I guess you're saying that *any* crank is good enough. Even
cranks from The Republic ?


Huh? I guess I'll say it s l o w l y for you. By saying one crank or
another is 'lighter/stiffer/more reliable', implys that others are
heavy/flexy/unreliable and that isn't true. Crank tests are like any
'test', are the stuff of magazines, bike stuff sellers. Very much like
wind tunnel tests of this or that, then applied etched in stone, to a
cyclist..crappola.

Saying it even more slowly for you - you made that stuff up. A general
statement with nothing behind it, except your reputation for being a crank
[sic -myself].

Light versus heavy is too easily measured. Rigidity, too. Reliability of
all of the current models is so high, I'm surprised anyone (except Mr
Brandt) makes noise about it.

And lest we forget - YOU sell things, too. Just like, but more directly,
the magazines you can't and won't read.

On another front - I just got a pair of Aksiums (Mavic's new cheapo
wheels) for winter use, and they have around 1000 km on them
already. Excellent wheels, IMHO. What would you have cooked up for
me for the price of 160 euros ?? Yes, bought at the local store,
not by mail or e-mail. --
Sandy

yep, these are $250 retail in the US...how about a Veloce or 105
hubset, double butted spokes(those are straight gauge, asian bladed),
a Velocity Aero or new Mavic 'sport' rim....better rear hub,
certainly, same price, less weight..but not French, tho, i guess
that's what sways you.

Mavic could be Indonesian or Coloradan, and it would mean no more than its
being French. The fact is that very few units of the enormous quantity
produced fails. Take out user error (crashing, etc.), miniscule amounts.
Unless you have real figures to prove me wrong, this remains true. And the
people who put the wheels together do it all the time, all day long, all
work week, not just in between promoting their Ergolever repair facility,or
dumping on innovation. They do that, QA is a further safeguard, and the
wheels sell because they work. Marketing - advertising - won't sell a
product for as long as Mavic has been around. You get a voice here because
it's an open forum, not because you're right. Repetition in advertising may
make some people believe things. Just like some may believe Mavic to be
inferior because you like to rant on your competitors.

And we still don't know your price. Figure the euros I quoted is equal in
dollars, as the VAT is included. So, for 160 USD, what do you sell ?
--
Sandy
Verneuil-sur-Seine

My rant to you was because you slammed the guy that asked for a source
of the information. It had nothing to do with wheels, everything to do
with him being 'allergic to print'.

Ya gotta get out more. Euros are not equal to dollars, not even close.
I just went to Milan and got 65 Euros for $100...$262 = $160 euros and
for that a Veloce hubset, DT dbl butted spokes, Velocity or Mavic
'Sport' rims...like I said before. Better rear hub, by far, probobly
lighter, probably more relaible and easier to fix, like I said before.

On 22 Oct 2005 06:18:58 -0700, "Qui si parla Campagnolo"
wrote:

Ya gotta get out more. Euros are not equal to dollars, not even close.
I just went to Milan and got 65 Euros for $100...$262 = $160 euros and
for that a Veloce hubset, DT dbl butted spokes, Velocity or Mavic
'Sport' rims...like I said before. Better rear hub, by far, probobly
lighter, probably more relaible and easier to fix, like I said before.

Doesn't work that way. Prices for bike and computer stuff are pretty much
the same number in euros as in dollars. The exchange rate is about 30% in
favour of the euro, but sales tax/VAT in europe takes care of about 20% of
that, and the other 10% is just things being generally more expensive
here.

Jasper

Dans le message de
oups.com,
Qui si parla Campagnolo a réfléchi, et puis a déclaré :
Ya gotta get out more. Euros are not equal to dollars, not even close.
I just went to Milan and got 65 Euros for $100...

Not quite - current exchange (today) is 1,19 USD for 1 euro.
Our VAT is in the price I quoted, at 19,5%, making it a wash, numerically.
No shipping.

$262 = $160 euros and
for that a Veloce hubset, DT dbl butted spokes, Velocity or Mavic
'Sport' rims...like I said before.

So for ONE HUNDRED dollars more, you come up with something OK. And when
you sell it by internet, it turns into "wheels in a box".

Better rear hub, by far, probobly
lighter, probably more relaible and easier to fix, like I said before.

As you have said many, many times before.

I'll take the nearly half-price deal. Not your "wheels in a box". Thanks.
--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

On Fri, 21 Oct 2005 17:23:51 GMT, wrote:
Jasper Janssen writes:

Simply to go for worst-case, I'd probably do it at the end of the
pedal.

There is a relationship between rotational torque and lateral bending,
both of which affect rigidity. Just the same, rigidity is not a
reasonable consideration with cranks that don't break, so I think the
whole subject is something for the weight wienies.

Depends on if nothing starts touching that shouldn't be touching from the
flexing.

However, why does the spider/chainring stiffness not matter? It's
not a safety issue (much), admittedly, but purely on stiffness and
energy-loss-into-flexing grounds it ought to matter, surely? There
are people around who've managed to collapse spider/chainrings,
while the cranks themselves took the load.

There is no significant flex in the spider and especially the
chainring. I rode on much flimsier CW spiders and rings in the days
of steel cranks and noticed no flex. Pedal flex is primarily in the
bicycle frame, not in cranks, crank spiders or chainrings. I think
the whole subject is off base because crank failure is the main
parameter of interest, the micro-motion of crank flex being trivial in
comparison. Just sit on your bicycle and push on one pedal. There is
significant motion but it isn't in the crank assembly.

Then how do people taco their chainrings? The flex as a result of pedal
loading may be in the cranks, bb, and frame, but the load coming from the
chain has to have an effect on CW/spiders.

Cranks have been made for a long time now and there is no excuse for
using the I-beam shape that is still popping up aplenty. Servo
brakes, and non linear brakes are no good in bicycles for the same
reasons they are no good on motor vehicles.

Power-assisted brakes seem to be used in many vehicles.


Jasper

Jasper Janssen writes:

Simply to go for worst-case, I'd probably do it at the end of the
pedal.

There is a relationship between rotational torque and lateral
bending, both of which affect rigidity. Just the same, rigidity is
not a reasonable consideration with cranks that don't break, so I
think the whole subject is something for the weight wienies.

Depends on if nothing starts touching that shouldn't be touching
from the flexing.

However, why does the spider/chainring stiffness not matter? It's
not a safety issue (much), admittedly, but purely on stiffness and
energy-loss-into-flexing grounds it ought to matter, surely?
There are people around who've managed to collapse
spider/chainrings, while the cranks themselves took the load.

There is no significant flex in the spider and especially the
chainring. I rode on much flimsier CW spiders and rings in the
days of steel cranks and noticed no flex. Pedal flex is primarily
in the bicycle frame, not in cranks, crank spiders or chainrings.
I think the whole subject is off base because crank failure is the
main parameter of interest, the micro-motion of crank flex being
trivial in comparison. Just sit on your bicycle and push on one
pedal. There is significant motion but it isn't in the crank
assembly.

Then how do people taco their chainrings? The flex as a result of
pedal loading may be in the cranks, bb, and frame, but the load
coming from the chain has to have an effect on CW/spiders.

I don't believe that is caused by CW or spider flex but rather extreme
chainline and frame flex that allows the chain to pull substantially
to one side. I climbed Filbert street in SF 31.5% in a gear large
enough to require a chain tension of at least 600lbs with no damage to
flimsy CW's. The chain line as off axis by 1.5 sprocket widths going
from the inner of two CW's to the leftmost of a five speed cluster.
That's not what CW benders are doing. They are in big crossover mode.

Cranks have been made for a long time now and there is no excuse for
using the I-beam shape that is still popping up aplenty. Servo
brakes, and non linear brakes are no good in bicycles for the same
reasons they are no good on motor vehicles.

Power-assisted brakes seem to be used in many vehicles.

Just the same power brake response is linear and on bicycles there is
no power other than the rider so that is not an option. Power assist
is only a multiplier, not a variable mechanical advantage.

Jobst Brandt

Sandy wrote:
Dans le message de
oups.com,
Qui si parla Campagnolo a réfléchi, et puis a déclaré :
Ya gotta get out more. Euros are not equal to dollars, not even close.
I just went to Milan and got 65 Euros for $100...

Not quite - current exchange (today) is 1,19 USD for 1 euro.
Our VAT is in the price I quoted, at 19,5%, making it a wash, numerically.
No shipping.

$262 = $160 euros and
for that a Veloce hubset, DT dbl butted spokes, Velocity or Mavic
'Sport' rims...like I said before.

So for ONE HUNDRED dollars more, you come up with something OK. And when
you sell it by internet, it turns into "wheels in a box".

Better rear hub, by far, probobly
lighter, probably more relaible and easier to fix, like I said before.

As you have said many, many times before.

I'll take the nearly half-price deal. Not your "wheels in a box". Thanks.
--
Sandy
Verneuil-sur-Seine
*******

Tell ya what Sandy, ask to buy something from me so I can say-no
thanks-also

On Wed, 19 Oct 2005 21:37:12 -0700, Jay Beattie wrote:

Actually, you don't have to log that many miles to break a crank. I
broke some Campys and an Ofmega with fairly low mileage -- and some
Campys with high mileage. Most recently, I was amazed to have broken a
Shimano Ultegra triple with probably less than 10K (although it is hard
to tell because it got switched around to a few different bikes). I was
pretty impressed with the Japanese cranks until then. All you can do
is watch for cracks, and for me, the failures have not been occurring
at the pedal eye, so the Jobst fix (chamfered pedal hole, washers,
etc.) would not have helped.-- Jay Beattie.

Wow. So where did yours fail? I have an Ultegra Triple that will
probably hit 10k in the next year.

Matt O.