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Broken Trek Carbon Steerer Tubes: Result of the Wrong Stems?

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Bryan Vaughans broken Trek Madone
Vaughan's broken Trek Madone.

Probably a cyclist’s worst fear when it comes to equipment failure, a broken steerer tube is nothing to joke about. It is understandable then that a select group of Mid-Atlantic racers is raising their concerns over their broken bikes. What isn’t clear is just why these forks are breaking, and what is to be done about it. While preliminary reports show less than 10 forks that have failed, it is enough to cause deeper looks into the matter by the companies involved.

The riders with the broken forks are blaming Trek, Trek is blaming use of stems that don’t meet Trek’s “carbon friendly” criteria, and both Trek and involved stem manufacturers such as FSA, are citing improper installation of the stems. In an article regarding the situation at hand on VeloNews.com, Tech guru Zack Vestal delves into the specific failures of various racers including the most vocal rider, Washington, D.C.,-area Category 2 road racer Bryan Vaughan. Bryan’s steerer tube came apart during a race much like a few other bikes which according to preliminary reports all seem to have been running FSA stems which do not adhere to Trek’s carbon steerer requirements. It also appears from the pictures that the bikes involved did not have a spacer above the stem, more on that later. By now you are sure to be asking, “Just what are Trek’s requirements and how are people supposed to know about them?”

Find out after the break.

From Trek's first carbon steerer tube tech bulletin
From Trek's first carbon steerer tube tech bulletin

Trek first brought light to the special considerations for a carbon steerer tube in an August 2009 service bulletin which was available to dealers on the home page of Trek’s B2B website. The bulletin stated that all bikes, regardless of steerer material should have at least a 5 mm spacer underneath the stem, and that all carbon steerers should have an additional 5 mm spacer on top of the stem to insure that the entire clamp of the stem was over steerer material. The bulletin also stressed proper torque and installation methods.  Then the bulletin was revised and reissued earlier this year with the release of the new 6 series Madones. It included all of the first bulletin with the addition of requirements of stems for carbon steerers.

Carbon steerer tube requirements.
Carbon steerer tube requirements.

To the left are images from the second service bulletin regarding stems on carbon steerer tubes. Years ago, even Trek sold stems that wouldn’t be acceptable according to these guidelines, but that was the reason for redesign of their stems. Currently all Bontrager stems adhere to the guidelines and are safe to use regardless of steerer tube.

The issues with other stems has to do with placement of cutouts, size of lightness holes, and even angle of the clamp bolts. Proper stems should have no clamp cutaways like pictures on the FSA stem to the left, as according to Trek’s engineers, the cutaways can allow the separate parts of the stem to dig into the steerer.

Also, the lightening hole inside the steerer tube clamp must adhere to a sizing guideline. The hole must have at least 10 mm of stem material between the edge of the hole and either lip of the stem. A lightening hole that is too large can allow the edges to gouge the steerer tube as the bars are muscled around.

Trek also makes it clear that stems that require a clamping torque of more than 6 nm are to be avoided, as higher torque values can crush a carbon steerer tube. Note that on components like a stem, the torque value printed on the part is the torque that the bolt and threads can withstand, not what the part being clamped underneath can withstand. Parts should only ever be torqued to the minimum amount of force that is necessary to keep the part from moving.

In the article that Zack Vestal wrote, FSA claimed that they didn’t know that Trek was stating their stems were unsafe for use with carbon, and that they are all riding the same stems on carbon steerers at the office without incident. FSA does however, blame incorrect application and installation of certain stems as possible cause for failure. They state that torque wrenches must be used and they recommend the use of carbon friction paste, as do many carbon manufacturers.

Carbon prep or assembly compounds are now available through many companies such as Finishline, TACX, and FSA and quite a few of them state that use of the product actually reduces necessary torque to keep the component from slipping.

Trek finally came out with an even more current tech bulletin (again front page on Trek’s B2B site, impossible to miss) today that included a letter for dealers to send to customers who have recently purchased a 6 series Madone. The letter is to inform customer of the special precautions needed for carbon steerers, not to inform them that there is a problem with their fork.

It is noteworthy that these particular cases all involve the same bikes, but these precautions are not just for Trek bikes. Every thing that Trek has stated in their bulletins is a very good idea for any bike that has a carbon fork. Easton, 3T, and Specialized all have similar service notices that specify things such as necessary amount of spacers, etc. As a service manager I have seen more bikes than I can count with damaged steerer tubes due to improper installation, bad equipment, or crashing. As bikes get more sophisticated, so must the level of care given to assembling and adjusting them.

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13 years ago

Ouch! I recently discovered that the top bolt of my FSA stem had crushed the carbon steerer of my RockShox SID WC fork. Luckily I have enough steerer left under the stem to hack off the affected section and salvage the fork.

I’d assumed responsibility rested with my friend over-torquing it when he borrowed my bike. This information would suggest that I owe him an apology.


13 years ago

Up to ~ 10mm of tube above the top of the stem engagement area will help resist the crushing force of clamping. As with any tube, the end of the tube is weaker because adjacent material is not available to lend support. I would therefore favor NOT cutting the end off of an engraved/damaged tube, but leaving it to lend whatever support it can against the clamping forces lower down. Expansion plug type and placement can also help offset clamping loads.

Graeme Freestone King
Graeme Freestone King
13 years ago

We at Velotech Cycling Ltd, have long advocacted placement ofa 5mm spacer above the stem and the use of expander bungs of a design that lend support to the inside of both carbon and also, crucially in our view, some of the lighter alloy and even cro-moly steerers.

This is part of our standard mantra for all threadless installations, so from our point of view it’s great to see our opinion reinforced by a company with the size and prominence of Trek.

As instructors in cycle maintenance and repair, we see some really lousy practice in shops, at the OE level, and a failure to understand many of the issues so eloquently discussed above. In particular, I can’t find myself agreeing more with the authour’s comment that “as bicycles become more sophisticated, so must the level of care given to assembling & adjusting them” … the time is long gone when a truly competent mechanic could do something the way “that 9s)he has always done it” … and consumers, too, need to be made aware of that.

It’s our opinion that cycle manufacturers have to do more to check the competence of the people they have selling their bikes & and that a refusal to sell to shops with untrained, unaccredited staff should be a plank in any bicycle manufacturer’s marketing strategy.

Maybe that way we’d get rid of some of the “back bedroom traders”, the box-movers and moderate the tendency to slash prices of some of the chains, as the costs of training staff start to filter through to the retail price – OK, it may add a small percentage to retail prices, but let’s balance that against safety, encouraging people to get into the sport and also the opportunity for technicians in shops to further their interest and competence in their chosen sphere of activity … maybe then shops would retain staff better too, so we’d all benefit by being served by staff with better product knowledge who feel valued by their employers 🙂

Jason Darrington
Jason Darrington
10 years ago

I have just been doing a little bit of research into the causes of steerer tubes snapping off as I myself have recently had an accident where this happend. I was on a ridley bike which had a ritchey stem on 4za carbon forks which have a carbon wrap steerer tube. It snapped while I was trying to pull away uphill leaving me needing hospital treatment and an operation. I have never had the need to remove the forks or the stem so have never overtightened the bolts. I now understand from what I have read that it is actually down to the fact that the bike wasn’t assembled correctly and that the fork should of been 5mm higher than the stem but if this is the case then how come pro team bikes all have flush stems with no top spacers.

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