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