New Carbon DuraAce cranks



nonns

New Member
Jul 10, 2006
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Hi Folks,

I'm just returning to cycling after a variety of car accidents/and years of wine women and song (and have spent a fair sum on a nice second hand bike with Durace Ace). I'm as much of a gadget and gear weenie as the next guy but ultimately. Isn't all of this a tad academic.

I mean unless you happen to be in the top 1% or 2% of cyclists out there is the flex going to make much difference once you've got to all carbon/top of the range alu and other exotic materials? Is the flex in Campy v's the flex in Shimano or somethig else really going to make a difference. If you're doing a long ride I would have thought that a little flex might be good for fatigue purposes in terms of taking some road shock fatigue out of the equation (which presumably could have an equally beneficial effect on performance). Likewise takign a slightly different line in the road avoiding some minor crack or bump could also have an effect.

I can't see that 1 mil of deflection on a crank is going to make the difference between me getting up the next hill and not. If I was Lance on the other hand and I had a fit Ullrich or Rasmussen next to me then pyschologically speaking it might make a difference.

Having said that I'm asking not telling so am interested to hear thoughts.

Oh and nearly forgot as this thread satrted out on the new Shimano carbon cranks personally I like the way they look but wish they didn't have Durace Ace plastered down the crank arm (looks tacky). Less is more.

My cranks say Time ASX and are in no way needing replacement (damn I'll have to wait ;->)






and I can't help but notice that
sideshow_bob said:
it's not only insignificant, it's also a single data point that is measured perpendicular to the crank axis on a jig.

a) the flex may or may not be linear as a function of force (or more accurately is probably linear over a range though the resulting slope will be different for different materials) applied, a single data point tells you exactly nothing.

b) the force is applied in a direction that generally doesn't see any significant force applied in a pedalling action, unless maybe you are sprinting and thowing the bike around between + and - 45 degrees from the perpendicular plane.

it's a marketing experiment nothing more and nothing less.

--brett
 

CAMPYBOB

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Sep 12, 2005
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That was an incredibly silly test!

I figured someone would say something like that...although it's more testing than they've done so far.

Go try it for yourself. There's got to be a shop near you with a an UT crank (or perhaps you have a friend that uses them) to go twist on.

Pygmalion effect aside, it's an easy comparison to make with at least SOME degree of validity.

Your assumption that I am somehow 'biased' is what is silly. I never held an opinion on the relative flexiness or stiffness of Campy UT crank arms until I owned them. And after damn near getting hit by a car by breaking an alloy crank arm I am most definitely NOT enamoured of alloy arms.

I discovered the flex while installing the pedals. The bike the UT cranks are installed on should, in theory, have the stiffest BB area of any bike I own...likely eliminating some of that 'noise' you keep refering to...and despite that bike having the only outboard (stiff) BB bearings and modern hollow (stiff) crank spindle in my collection.

I can put it no more simply than to state again; the UT arms move more and more easily. Subjective?...objective?...it's close enough for government work, as they say.

Does that matter? Probably not, but it is the case. At least as far as regards the limited sample of parts I've used.

Go try my 'silly' test for yourself.

While you're at it, give a few pulls and pushes on a pair of FSA Energy bars, Then try to blame the stem...or steerer tube...or fork...or whatever else it's attached to while easily observing the drop flexing in relation to the flat.

Yup. From now on I'm discounting common sense and 'wildly inaccurate' human observations.

And BTW, I work with Pratt & Whitney, Rolls Royce, General Electric, Allison, Rocketdyne, Brown Boveri, Munchen Turbine, etc. We have parts on every major turbine motor, including the space shuttle main motors. No kites.
 

nonns

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Jul 10, 2006
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Please excuse me. I never intended any offence. I never implied that the test was silly. I was simply asking whether in the general scheme of things how much difference will crank stiffness make when you think that the whole contraption (bicycle) creaks and groans and flexes away under you. Well I'm assuming that mine must creak groan and flex under me cos I'm overweight. I'm not strong enough yet to pull the skin off a rice pudding so I'm not that bothered by stiffness of cranks just yet! :->

Personally if I was noticing an increasing flex in a crank I'd want to get it checked out just in case it was faulty. I've seen a crank fail and the guy who was riding the bike at the time wasn't a pretty sight afterwards.




CAMPYBOB said:
That was an incredibly silly test!

I figured someone would say something like that...although it's more testing than they've done so far.

Go try it for yourself. There's got to be a shop near you with a an UT crank (or perhaps you have a friend that uses them) to go twist on.

Pygmalion effect aside, it's an easy comparison to make with at least SOME degree of validity.

Your assumption that I am somehow 'biased' is what is silly. I never held an opinion on the relative flexiness or stiffness of Campy UT crank arms until I owned them. And after damn near getting hit by a car by breaking an alloy crank arm I am most definitely NOT enamoured of alloy arms.

I discovered the flex while installing the pedals. The bike the UT cranks are installed on should, in theory, have the stiffest BB area of any bike I own...likely eliminating some of that 'noise' you keep refering to...and despite that bike having the only outboard (stiff) BB bearings and modern hollow (stiff) crank spindle in my collection.

I can put it no more simply than to state again; the UT arms move more and more easily. Subjective?...objective?...it's close enough for government work, as they say.

Does that matter? Probably not, but it is the case. At least as far as regards the limited sample of parts I've used.

Go try my 'silly' test for yourself.

While you're at it, give a few pulls and pushes on a pair of FSA Energy bars, Then try to blame the stem...or steerer tube...or fork...or whatever else it's attached to while easily observing the drop flexing in relation to the flat.

Yup. From now on I'm discounting common sense and 'wildly inaccurate' human observations.

And BTW, I work with Pratt & Whitney, Rolls Royce, General Electric, Allison, Rocketdyne, Brown Boveri, Munchen Turbine, etc. We have parts on every major turbine motor, including the space shuttle main motors. No kites.
 

CAMPYBOB

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Sep 12, 2005
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I never intended any offence.

None was taken.

In the grand scheme of things, a small amout of crank flex is insignificant.

None the less, it exists and is more pronounced with the larger and more powerful riders.

Some components have been designed with so little regard to strength or durability that rider weight limits and/or replacement schedules are specified. I haven't seen that with cranksets so far.

I've seen a crank fail and the guy who was riding the bike at the time wasn't a pretty sight afterwards.

Immediate and unexpected loss of control is never a good thing. Unbalanced face-plants are often the aftermath.

Years ago, when my left crank arm snapped off, my foot hit the pavement and this stripped the Super-Record pedal right off my cleat (I retrieved it from the centerline of the road afterwards) as i did an instant and uncontrolled left turn across a line of oncoming cars. Only luck timed it that i shot in between two vehicles and off into some one's front yard. While i didn't drop the bike (again, more good luck, not skill), I was completely out of control.

I don't think my new Chorus UltraTorque is faulty in any way...I just think it's a bit more flexible than my other cranks.

I an not noticing an increase in flexation. I noticed the crank was flexing on day one, when I bolted the pedals onto the arms...the arms moved more than what I've been used to seeing.
 

dhk2

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Aug 8, 2006
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sideshow_bob said:
it's not only insignificant, it's also a single data point that is measured perpendicular to the crank axis on a jig.

a) the flex may or may not be linear as a function of force (or more accurately is probably linear over a range though the resulting slope will be different for different materials) applied, a single data point tells you exactly nothing.

b) the force is applied in a direction that generally doesn't see any significant force applied in a pedalling action, unless maybe you are sprinting and thowing the bike around between + and - 45 degrees from the perpendicular plane.

it's a marketing experiment nothing more and nothing less.

--brett
OK, I'm still confused as to what bending is being discussed. As you state, would expect the load to be applied, and deflection measured perpendicular to the axis. EG, the crank arm is held horizontal at the spindle end, with load is applied to the pedal end (at the center of the pedal axis), and the "sag" is measured from the horizontal reference line.

Your "b)" leads me to believe the 124 lb load was applied parallel to the axis, ie, by load pushing into the centerline of the bike, and deflection measured on the same axis. Surely the test isn't that dumb :)
 

CAMPYBOB

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Sep 12, 2005
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To my mind, I prefer the test fixture pictured in this link: http://www.biketesting.com/samplecrankreport2006.pdf

Note the low weight loads...that still yield deflection. I would like to see the arm deflection measured with the arm in a vertical postion also. And while crankarms may not be subject to massive shock loading, I would like to see the result of impulse loading on deflection.
 

dhk2

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Aug 8, 2006
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CAMPYBOB said:
To my mind, I prefer the test fixture pictured in this link: http://www.biketesting.com/samplecrankreport2006.pdf

Note the low weight loads...that still yield deflection. I would like to see the arm deflection measured with the arm in a vertical postion also. And while crankarms may not be subject to massive shock loading, I would like to see the result of impulse loading on deflection.
This set up looks realistic since it applies load on the pedal spindle. The figures shown are obviously much greater than those on the graph you posted, which implies to me that torsional twist of the crank arms is a much bigger factor than straight beam bending deflection (likely not included in the first graph test procedure).

In fact, it's hard to believe that so much deflection exists. With the values shown (eg, 400 lbs/in) would think they should be measureable by a helper with a ruler on the garage floor while a rider goes from sitting to standing on the pedals.
 

ScienceIsCool

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Jun 25, 2006
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The setup is flawed, unfortunately. The chain will also flex, causing movement. It's possible that the anchoring point is also flexing. That's why the numbers are so large and are possibly not representative of the crank.

John Swanson
www.bikephysics.com
 

CAMPYBOB

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dhk2 said:
In fact, it's hard to believe that so much deflection exists.
All one need do to see the deflection is simply grab a pedal and try twisting the crank arm. If it moves by hand pressure it damn sure is moving more under foot.
 

CAMPYBOB

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ScienceIsCool said:
The setup is flawed, unfortunately.
If so, it's flawed equally for all cranks and the numbers while not exact are at least proportional and still representative.

Again, I suggest we focus on the big picture...crank arms flex. That's why these folks are at least attempting to quantify it. Some move noticeably more than others. No fixture is required to illustrate it in some cases.
 

sideshow_bob

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Apr 26, 2005
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CAMPYBOB said:
If so, it's flawed equally for all cranks and the numbers while not exact are at least proportional and still representative.
That doesn't make sense. If a part has been engineered for strength/rigidity (or some other property) in a particular orientation, why does a test that measures that property in a different orientation represent anything, comparitive or not? You might say you are comparing apples and oranges.

--brett
 

CAMPYBOB

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Sep 12, 2005
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To address John's points in more detail:

The chain will also flex, causing movement.

If the same chain is used as a rotational locking mechanisn for all crank modelss, the displacement read error, if indeed there is one, will be the same for a given load.

It's possible that the anchoring point is also flexing.

Again, all things being equal, if the crank pivot point is located the same for all models, the error (again...if error at this point actually exists at all) will be equal for all models tested at a given load.

That fixture, like the one referenced before it, is plenty close enough for government work.

I suppose we could also bring up the minor amount of theoretical chainring 'wind up' and/or how the spindle/arm joint affects stiffness, but it's all apart of an inseparable package on the bike in most cases anyway.

To me, it's all splitting hairs.

I agree with you that, so far, none of the fixtures address the stresses a crank arm sees as mounted/used on a bicycle.

Such a gage would be much more complicated and expensive. Like I ask my customers when they want a gage or fixture designed...How much money do you have? What resolution are you looking for? What repeatability level is acceptable to you? How skilled are your gage operators? etc.

Again, in my opinion the above fixtures are probably close enough to get a good feel for how 'flexible' the arms are. So is going out to our garages and just giving it a few good twists and tugs.
 

kevinbob

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Sep 11, 2007
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i think that actually looks better than FSA K-force cranks with the hollow centre