Installation as critical as design
Regardless of the stem design, incorrect installation causes serious problems. FSA’s Tech and Warranty Manager Bryan Wielgasz weighed in on this point.
“Sometimes when components don’t seem secure at a recommended torque, it may be natural instinct to tighten the bolts further; over-tightening the bolts and creating a stress point between the steerer and the edges of t he pinch bolt area of the stem,” he said.
“Recommended torque will vary between stem manufacturers, with stem design, and the types of bolts used.”
Wielgasz pointed out that FSA stem bolts are marked with a maximum torque value for the bolt, but that doesn’t necessarily mean the part needs to be tightened all the way to that torque – it’s a max torque value for the bolt in the stem, but it doesn’t necessarily apply the steerer being clamped inside. “A trained mechanic should only apply the amount of torque needed to secure the part. Rarely should maximum torque need to be applied,” he said.
Wielgasz also suggested that if tightening the stem clamp bolts to recommended torque still fails to adequately secure the stem on the steerer, a mechanic should check the stem inner diameter and compare it with the steerer tube outer diameter to see if one or the other part is out of tolerance.
Ralph commented that correct installation by a trained mechanic is harder to ensure when parts are delivered not through a bike shop, but direct to customers via mail order, sponsorships, or eBay. He added that almost every carbon component interface is significantly improved with carbon fiber friction paste or assembly gel, because it corrects irregularities in the interface between mating surfaces, dramatically reducing the torque required to secure a carbon part.
Citing an example, Wielgasz pointed to tests demonstrating that using carbon paste can reduce the necessary torque to secure seatposts in frames by half. He said it would be safe to assume a similar (though not identical) reduction in the torque needed to secure a stem on a steerer, making for a healthier steerer tube and safer riding situation. “All our carbon seatposts come with friction paste,” he said.
A stock installation also results in steerer tube fracture
Paul Wilson was not using an FSA or an Easton stem, and never did. When his 6-Series Madone steerer broke, he says he was using a stock Bontrager Race X Lite aluminum stem, tightened to spec with correct spacers above and below.
“Everything was stock Bontrager,” said Wilson. He knows because an experienced Trek dealer assembled his bike, which was delivered complete from Trek.
“We used everything stock and everything to the letter,” he said.
Dean Gore at Trek suggested that perhaps inadvertent over-tightening of stem bolts could have been the culprit in this case. “The presumption of torque spec is one of the bigger issues we are dealing with here,” he said. “Torque spec on a carbon part can’t be presumed. A torque wrench is a tool that consumers and shops need to use when dealing with carbon parts.”
Matt McGoey, the owner of All American Bicycle Center in Damascus, Maryland, where Wilson’s bike was shipped and assembled confirms that it was correctly built. “I can’t explain it,” said McGoey, “but I’m confident (Trek) is on top of it.”
Wilson’s fork has been returned to Trek and is in process for replacement under warranty.
Trek takes action with communication and adds more carbon
Dean Gore said that Trek first heard from Bryan Vaughan on May 16th. The company takes failure reports extremely seriously.
“The first step is to get the product back to Trek Waterloo for proper evaluation,” he said. “With over 30 carbon engineers on staff in Wisconsin, issues like this can be approached with a great understanding of how carbon structures behave. A full evaluation in this case included replicating the problem in our Waterloo test lab — a procedure which has given us high confidence that we fully understand this steerer issue,” said Gore.
The reported failures, however, wouldn’t represent the first time a bike product survived lab testing but failed in the field. Cervelo, for example, recalled a True Temper-made carbon fork in 2008 after discovering failures in the field despite the fork having passed U.S. and international testing.
Trek has issued four increasingly specific dealer bulletins about carbon steerers, starting in August 2009. Recently the company has talked with the CPSC about a consumer notification.
Furthermore, Trek is now adding material to 6-Series Madone steerer tubes. “Even though the current steerer passes all of our of standards for durability, we are adding carbon plies to the layup of this carbon steerer to reduce the probability of future issues,” he said.
Nevertheless, Trek is not about to rescind the original installation guidelines. “We want to be clear that even though we are adding material to the steerer, consumers must still use the right stem, the right spacers and the right torque. High-end carbon fiber structures will always require proper installation and care,” said Gore.
Are cracks in communication leading to cracks in carbon?
Trek feels that the dealer bulletin is adequate for educating retailers, and by extension, owners of Treks.
But eight of the ten Trek dealers contacted by VeloNews weren’t aware of the service bulletin.
Matt McGoey at All American Bicycle Center received the most recent bulletin by email just a few days before Wilson’s steerer tube failed. “I emailed most of my customers that have Madone bikes,” he said.
Jake Nie, service manager at University Bikes in Boulder, Colorado, was also aware of the bulletin. His shop has regular morning staff meetings to distribute information to all mechanics and staff. “So when a mechanic does see a 6-Series, they’re going to pull it aside and check that it’s OK,” he said.
One service manager was able to find it on Trek’s dealer site after searching for five minutes.
“I firmly believe that Trek has been more proactive than any other manufacturer,” responded Gore.
He shared four bulletins regarding carbon steerers sent to dealers in the last year, starting in August of 2009. The bulletins become increasingly specific about acceptable stem-design characteristics, spacer placement, and stem clamp bolt torque.
Explicit assembly instructions are not unusual
Explicit installation instructions are not unique to Trek. Easton and 3T forks both come with instructions specifying minimum and maximum placement of spacers above and below the stem. Specialized also has specific instructions, like Trek recommending against the use of stems with large cutouts.
Easton composites engineer Chuck Teixeira said he’s seen fork steerer tube damage spread down from the very top of the steerer due to lack of stem overlap at the top. He recommends a spacer above the stem. If the stem pinches the top of the steerer, it can crush the carbon and cracks can form and propagate down the steerer.
Teixeira said in ten years he’s never seen a steerer break below the stem and noted that most lab tests on forks evaluate durability in the legs, not the steerer.
Teixeira is a proponent of carbon steerer tubes because of the complexity of bonding dissimilar materials. He feels that a one-piece carbon fork will usually be stronger than a two-piece aluminum/carbon fork.
Calling the Feds
Not satisfied that enough was being done, Vaughan filed a report with the CPSC on May 25.
“All Trek would tell me is were going to send out a dealer notice. I don’t think dealers know about those things, I don’t think they’ll read them,” said Vaughn.
“I think you can debate a lot of the other technical things about carbon and ‘Did Brian overtighten his bolts,’ and all that – fair enough. But once you dig through that, I think there’s really no debate that you get to the point where there are identifiable failures with different stem combinations and different install situations that were borderline catastrophic or catastrophic. Once you know that, what do you do about it? That’s the question,” he said.
Vaughan’s concern is that Trek’s installation guidelines are too narrow, too specific, too easily overlooked, and not widely known. “My particular confluence of circumstances – my way of putting it is that it proves with two or three really kind of innocent consequences at play you could end up in your face in the gravel like I did.”