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PostPosted: Sat Aug 05, 2006 10:05 pm 
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Seems like pulsions are all starting to simultaneously fail... :?


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PostPosted: Sat Aug 05, 2006 10:07 pm 
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brianwchan wrote:
Seems like pulsions are all starting to simultaneously fail... :?


Brian... its a conspiracy I tell you... the French are getting back at all American cyclists!


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Posted: Sat Aug 05, 2006 10:07 pm 


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PostPosted: Sat Aug 05, 2006 10:19 pm 
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lol yeah, but it does seriously turn me off from them. Has anything like this happened to their other cranks? Or is it just the pulsions?


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PostPosted: Sat Aug 05, 2006 10:42 pm 
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Just like my (and others) EC90 bars, now the pulsions, zipps rims, and Mr Zs DA crank are from his SRM. Stuff breaks. I think we (WWs that is) are more prone to seeing this happen (around here) because we all have this stuff.

I'm currently ridding on a Pulsion (w/ergomo BB) and they have been solid. I have a set of unused DA cranks that I'm keeping around. Just because MrZs (da crank arm) broke doesn't mean mine will. I think it might be a fluke thing. Maybe that had a few bad ones. Typically, if this thing happens alot they will have to do a recall.

Glad your unhurt.

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Last edited by STARNUT on Sun Aug 06, 2006 4:57 am, edited 1 time in total.

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PostPosted: Sat Aug 05, 2006 11:02 pm 
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Glad my Pulsion are only on my hill climb bike...


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PostPosted: Sat Aug 05, 2006 11:20 pm 
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Quiere carbon, guys, coje carbon!!!!

There are certain applications where carbon just does'nt make sense, like crankarms.

Lighter maybe by a few grams, but not as stiff as aluminum and given the fact that this type of failure can get you and others seriously hurt, I wonder if there are any WW members who are still hell-bent on getting carbon cranks.

I'm glad you were'nt hurt, brother. And too bad about your frame. Keep us posted on that, as from what I see the damage to it was not your fault. Maybe the Stronglight company owes you a new frameset as well.


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PostPosted: Sun Aug 06, 2006 12:18 am 
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J-Nice wrote:

There are certain applications where carbon just does'nt make sense, like crankarms.

Lighter maybe by a few grams, but not as stiff as aluminum and given the fact that this type of failure can get you and others seriously hurt, I wonder if there are any WW members who are still hell-bent on getting carbon cranks.



Not true.

I agree with the post that mentions we see it more, because alot of WW's have these kinds of products. But on the whole the incidents are very small. There are tons of those cranks out there, and we've seen a couple fail.

Perhaps aluminum does make a stiffer arm, but not better. Al and carbon fail in different ways. Which is probably why Rich is still ok. Carbon breaks are generally not instantaneous. Even if they are quick, they usually give you a split second to ease up, or shift your weight.(not just cranks, but handlebars etc...) When al breaks it usually snaps very quickly leaving a rider off balance and crashing.

I've seen plenty of broken Dura Ace, Campy al cranks.

It's really not all about the material but the manufacturing as well. Bad ones will always slip through. It's about what percentage of the ones coming out are bad.

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PostPosted: Sun Aug 06, 2006 12:29 am 
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Also on J-Nice's post, you say that carbon cranks will never be as stiff as Aluminium cranks. Why then, in a range of cranks (both Al and Carbon) tested for stiffness, did the Ultegra win, then the Time Carbon, which beat a range of both carbon and aluminium.

You cant really make a blanket statement of Carbon never being as stiff as Al, as stiffness depends more on manufacturing and engineering than the basic properties of each material.


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PostPosted: Sun Aug 06, 2006 12:50 am 
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Carbon is supposed to have the highest specific strength among Carbon, Steel, Aluminum, and Ti (if I remember my engineering materials text book correctly)

What that means is for a given sized object made from all of those materials the carbon will be the strongest. The design of all of them can be pushed beyond their structural limits though....for any material that is.

Honestly I think the Pulsions are on the ragged edge....that's what we WW's like though right?

Edit: I said that wrong. For a given mass of all of these materials carbon will be the strongest. Carbon per volume is the lightest. So to design an equivalent stength structure to aluminum, Ti or Steel it has to be bigger. That's why we see a lot of fat carbon tubes on frames and such. The old steel frames were made with small tubes. Then you saw aluminum come along and the tubes started to get fat. Same with Ti only not typically as fat as aluminum. And now carbon.

So for something like a carbon crank to achieve the same strenth as an aluminum crank it needs to have an oversized structure and the wall thickness needs to be greater. How do you do this with the spider where the chainrings mount up :?: You can't because that's one of your design constraints that's why you saw such a failure as the chainring bolts shredding through the spider holes in this thread. http://weightweenies.starbike.com/forum ... ht=pulsion
IMO this part of the crank should be made out of alloy.

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Last edited by drjones96 on Sun Aug 06, 2006 3:06 pm, edited 3 times in total.

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PostPosted: Sun Aug 06, 2006 12:58 am 
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Not when my arse is on the line no :cry:

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PostPosted: Sun Aug 06, 2006 1:43 am 
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madcow wrote:
Which is probably why Rich is still ok. Carbon breaks are generally not instantaneous. Even if they are quick, they usually give you a split second to ease up, or shift your weight.


FWIW, it felt just like popping out of the pedal, except my foot rolled to the outside.


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PostPosted: Sun Aug 06, 2006 1:52 am 
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I think what Jason was saying was that there were probably cracks that you didn't notice (or couldn't see) before the failure.


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PostPosted: Sun Aug 06, 2006 2:01 am 
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520 Dan wrote:
I think what Jason was saying was that there were probably cracks that you didn't notice (or couldn't see) before the failure.


I agree... if you look at the pic, there is a crack running lengthwise between the pedal axle insert and the 'hole' in the crankarm... its likely that happened first, perhaps from rough roads.

Then just enough torque caused the crack to spread, allowing the threaded axle insert to rip out. I think the damage to the end of the crankarm was the result of the insert ripping out.


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PostPosted: Sun Aug 06, 2006 2:44 am 
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glad you are not hurt, rich. i've never had a problem with pulsions, but i may not be stressing enough like hard sprints.


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PostPosted: Sun Aug 06, 2006 4:08 am 
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What I'd like to know.. In this situation where a manufacturer's product fails like this and damages the frame or other parts as a result.. Do manufacturers normally reimburse you for the frame etc that you wrecked?...

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Posted: Sun Aug 06, 2006 4:08 am 


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