Long story short, from the product's user : "I was out for my first road ride in awhile and as I was riding away from a stop sign I heard a mysterious crunch and my left hand became unweighted. I looked down to find my beloved Zipp B2 carbon bars fracture under my own power. This event was even more surprising because the bike has never even fallen over let alone been involved in a crash."
The fracture was to the left of the stem clamping plate. Someone did a high resolution blow up of the image and found a neat crack running at the bottom of the handlebar.
Is this why Zipp recommends running their own carbon stems with these bars? Or is it just another avenue to make more money. Both I would guess..(?)
Since he said the bike never took a fall, we might speculate that this is a clamp over tightening related issue? Its still scary. Imagine if this would happen at a race or while going downhill. Sheesh.
Monday, June 30, 2008
14 Zipp B2 Handlebar Failure
Photos courtesy of Weightweenies
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My guess is the clamp was overtightened. That is the first thing people need to do when they start adding carbon parts to their bikes - buy a good torque wrench.
ReplyDeleteI don't trust carbon controls so I ride alloy.
Ron: Not an engineer, but I don't think I need to be to tell you that you NEED A TORQUE WRENCH when you start to bolt on carbon. I would go along with the fact that this was likely over-tightened. It even looks as though that crack is right at the edge of the clamping plate.
ReplyDeleteI'm with the others, get a wrench.
ReplyDelete-B
Gotta go along with over tightening on this one. A horizontal crack leading from the bottom side of a fulcrum point. They make some inexpensive torque wrenches now just for this type of thing.
ReplyDeleteDon't know where these particular bars came from, but there have been counterfeit Zipp bars sold on eBay - here's the warning from the Zipp web site: http://www.zipp.com/Support/CounterfeitHandlebars/tabid/176/Default.aspx
ReplyDeleteAnon : Good info. I wasnt aware of this.
ReplyDeleteOver tightening sucks and happens.
ReplyDeleteIs there a fix other than buying a torque wrench? Perhaps there is a design change that would aid in carbon cracks?
I might suggest wider stem clamps with solid bolt plate faces. This will: 1- give more surface area to hold on to so bolts don't need to be tight in the first place and 2- Reduce the stress concentration at the clamp (where there are many forces already)
Yeah, get a good torque wrench but like Chris, for now I'm sticking with alloy.
ReplyDeleteNote that this particular stem has a 2 bolt design as opposed to a 4.
ReplyDeleteI would prefer the latter, and would argue that bolting stresses are more spread out with that arrangement. Not sure what some of you might think of that. 2 bolts, not so good in my books, especially with carbon bars.
That sucks, but if it make you feel any better, I broke a titanium handlebar mountain biking. The left side snapped right off going over a 12 inch drop. I'm now a firm believer in the power of steel. At least it will bend before getting catastrophic.
ReplyDeleteRon: Agree, I think you'd be more likely to try to really crank down two bolts over four due to tightness and slippage. I just think the pressure spread out from four would hold better.
ReplyDeleteI’m still a believer in carbon. The weight and comfort benefits, if the bar is installed properly, far outweigh the minimal disadvantages. Keep in mind that the forces that would cause the catastrophic failure of a carbon bar would definitely damage an alloy bar beyond safe use, not to mention that you’d be hitting the pavement/dirt anyway. Bicycles are much more technical now than they were 25 years ago and need to be treated as such. Every week I have home mechanics coming into my store with problems that arise from improper assembly... That they want warranty coverage for I might add.
ReplyDeleteI'm a big alloy fan for bars/shifters/cranks since those take the brunt of the crash when there is one. More often than naught if you lay down a bike with carbon extremeties it's going to shave or crack which in turn compromises the integrity. Bash alloy and it has a better chance of holding up for the rest of the race.
ReplyDeleteFour bolt patterns vs. two bolt considering tightening. You have the same risk in overtightening the bolts. 4 bolt is a better clamp and it pushes the pivot point from an hourglass to a square meaning more stability.
Good insights.
ReplyDelete