New Carbon DuraAce cranks



mikesbytes

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Apr 12, 2006
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So what you guys are saying is the the difference in stiffness is really just nit picking.

With the selection of products on the market, how do you select the one thats right for you?
 

BikingBrian

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Sep 25, 2003
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mikesbytes said:
So what you guys are saying is the the difference in stiffness is really just nit picking.

With the selection of products on the market, how do you select the one thats right for you?

Exactly. So just pick the one you think looks nicest and fits your budget :)
 

cdy291

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Nov 23, 2006
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Lets just all go to Walmart and get our bikes, since technically there just as good and should be just as fast.
 

alienator

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Jun 10, 2004
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cdy291 said:
Lets just all go to Walmart and get our bikes, since technically there just as good and should be just as fast.

We never have to wait too long for the stupid generalization. Thanks for keeping our wait short, cdy291.
 

Dietmar

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Jun 9, 2006
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ScienceIsCool said:
Vertical compliance, harshness, and smoothness of ride!? Hahahahaha. There is no vertical compliance to a rigid truss structure.
Hahahahaha. Earth to John: The concept of a rigid truss structure is an idealization, and there are no rigid truss structures in reality. All real truss structures, including bicycle frames, do have some compliance. Different frames have different amounts of compliance.

ScienceIsCool said:
I'd put five year's wages on actual accelerometer measurements not matching rider expectations or perceptions.
Expectations, sure, those may be misleading in any number of ways, and for any number of reasons. Perceptions, though, are usually a lot more accurate than you give them credit for. I'd stay away from that particular bet, if I was you...
 

ScienceIsCool

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Jun 25, 2006
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Yes, yes. And when I sneeze the earth changes orbit. If I spin counter-clockwise the earth's rotation speeds up. And truss-like structures have vertical compliance...

John Swanson
www.bikephysics.com
 

lava

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Feb 16, 2005
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I think the latest Shimano crank designs look totally awesome without the center bolt hole. This one is no exception.
 

Dietmar

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Jun 9, 2006
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ScienceIsCool said:
Yes, yes. And when I sneeze the earth changes orbit. If I spin counter-clockwise the earth's rotation speeds up. And truss-like structures have vertical compliance...
alienator said:
We never have to wait too long for the stupid generalization.
Couldn't have said it any better.
 

CAMPYBOB

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Sep 12, 2005
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alienator said:
http://weightweenies.starbike.com/phpBB2/download.php?id=19037

Now this is where Ohio's village idiot, CampyBob, tells us that he's able to discern such small differences in crank stifness with his body. This is where CampyBob explains what he knows about stiffness and engineering and how adept and sensitive he is to very small deflections in crank arms.
Now, this is where Arizona's moron, Alienator, tells us...well, nothing. Hey, have you found a job yet? Thanks for re-cycling my village idiot line...how typically unimaginative of you. It was as predictable as your pathetic and pointless response. At least you are helping save the planet with your re-cycling and Soobie though. Keep up the good work, ****stick. Oh, and how's those CNC pulleys doing at saving your energy?

All one needs to do is use two fingers to try and flex something like an old C-Record arm or Record alloy crank arm and then a carbon Record arm. The carbon arm moves with noticeably less force and more distance. Grab the pedal axle and try to twist the arm. It doesn't take NIST calibrated fingers to prove the obvious.

Maybe you can't feel it under foot with your flexible flyer Moots. Perhaps you should try something with a stiffer bottom bracket. Maybe a Schwinn Varsity will help you model the expiriment to your high standards of engineering excellence.

The flex may, or may not, affect efficiency, ride 'quality' or whatever specific parameter you wish to discuss. Good, bad or indifferent the carbon arms are more flexible. Period. Am I going to toss my Campy carbon? Nope. Are they as stiff as my old Campy alloy arms? Nope. If more grams of material were added, the carbon arms would be as stiff. The rush to shave weight is resposible for the decreased stiffness.

Perceptions, though, are usually a lot more accurate than you give them credit for.

Exactly.
 

bobbyOCR

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Aug 31, 2005
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Ah, you also never have to wait long for an argument to break out where there is a fact vs marketing conflict.

It is a butt ugly crank. It may suit some bikes, some people may like it. If it does weigh 706g for the set, it gives Shimano users a lighter option. Substituting the RED crankset with this also makes RED a lighter groupset, and arguably better performing.

A 10% increase in stiffness means it will be nearly 20% stiffer than Record. Although in real world terms this counts for nothing, it is a nice thought to have when you are trying to extract every ounce of performance from yourself and your bike.

Alloy DA will still remain benchmark in price:weight:'performance' ratio
 

ScienceIsCool

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Jun 25, 2006
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Dietmar said:
Couldn't have said it any better.
It's not a generalization. It's a tool of rhetoric called 'reductio ad absurdum' and I was using it to draw attention to the fact that it is quite ridiculous to ignore the main point of the argument and focus on an entirely insignificant, semantic side issue.

To reiterate, I can only think of a handful of parameters that affect the way a frame will ride. I believe that manufacturers have added stiffness to that list as an easily understood differentiator and not because there are any performance benefits.

John Swanson
www.bikephysics.com
 

CAMPYBOB

Well-Known Member
Sep 12, 2005
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I believe that manufacturers have added stiffness to that list as an easily understood differentiator and not because there are any performance benefits.

Since there is no performance benefit, I take it we'll all be riding frames made of al dente spaghetti next season?
 

ScienceIsCool

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Jun 25, 2006
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CAMPYBOB said:
I believe that manufacturers have added stiffness to that list as an easily understood differentiator and not because there are any performance benefits.

Since there is no performance benefit, I take it we'll all be riding frames made of al dente spaghetti next season?
Ah, yes. You are also trying to use reductio ad absurdum... If you do an order of magnitude estimate of the power lost into a whippy frame like a Vitus (stiffness numbers can be found online for many frames) you will see that it is small to the point of being negligible.

However, once you get to a certain point of frame flexibility the bottom bracket moves enough to affect the drive train. You can get "automatic" shifting because of changes in tension in the derailleur cables. Things can start to rub. Also, some people don't like the feel of the bottom bracket shell moving around a bit during hard efforts. Never stopped Sean Kelly, but there you go.

In other words, there are limits on how "al dente" a frame can be made before there are issues with how it behaves. This limit is a long ways away from the point where efficiency is reduced in any meaningful way.

John Swanson
www.bikephysics.com
 

CAMPYBOB

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Sep 12, 2005
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Things can start to rub.

Exactly. I found that out last year with a Litespeed...flexible in the BB.

Al dente to the point of being trash.

Even if I was not putting out enough watts to force rubbing a tire on a chainstay it is still having an effect on efficiency. Strain gages and LVDT's aside, it IS discernable from the saddle. It doesn't take an order of magnitude nor even products from different eras.

Sean Kelly's propensity for riding his free-of-cost team supplied framesets didn't do much to stop the locals from selling off their flexible-flyer Vitus **** from the 1980's either. No one wanted them. Even the ones that stayed in one piece were soon in storage or for sale to the inexpirienced. The pro's riding self-destructing Mavic discs, carbon rims that fold up under slow impact with dogs or frames that end up in pieces after a fall are indicative of another issue that folks claim there is little or no performance improvement...weight.

Do carbon crank arms eat watts in any appreciable degree? I don't know, nor do I care. The flexing is easily seen with a simple test though. Marketing? Not to me. I'll take strong and stiff crank over a strong and flexible if i have a choice. I'm hoping Campy's third gen arms are stiffer.

Either that or just tracking down a good used 1974 Varsity with steel rims!:D
 

ScienceIsCool

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Jun 25, 2006
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I loved my Vitus 979... Sigh. I wish I still had one. I got it second hand when I was a student and raced on it for several years. I sold it to a friend of mine shortly after I left university and wish I hadn't.

John Swanson
www.bikephysics.com
 

CAMPYBOB

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Sep 12, 2005
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SIC, what did you weigh when riding your Vitus?

I had the unique expirience of watching an early one come unglued (literally) in front of me. Failure at the seat stays locked up the rear wheel. Not a pretty picture after that.

I wish I had not sold my 1972 Peugeot PY-10...now THERE was a study in flexure! Descending with knees tightly clamped to the top tube and still shitting myself when the fork shuddered. Damn those seamed forks!