(Editor’s Note: The following letter was sent to VeloNews technical editor Zack Vestal in response to questions about Madone steerer tube breakages.)

Zack –

We appreciate VeloNews looking into this issue as the racing community needs to better understand the consequences of ignoring installation instructions when dealing with carbon fiber parts.

As the technology going into today’s bicycles has increased, so has the responsibility of the mechanic and rider to follow the manufacturer’s installation instructions exactly.

This issue is not unique to Trek, but is specific to carbon steerers from every manufacturer. The consequences of not following manufacturers compatibility directions are real and potentially serious.

There are 3 issues to remember when clamping a stem to a carbon steerer tube:

1. Use a torque wrench. Always and every time. As with any carbon part, over torquing the stem clamp around the steerer will compromise the carbon structure. This is not a new issue and most racers understand this. But the consequences of over torquing a carbon steerer are real and can be catastrophic.

2. Use spacers above and below the stem- always. This is not as obvious as over torquing, but riders must have a minimum of 5mm and maximum of 40mm of spacers between the stem and the headset. In addition, a 5mm spacer is required above the stem. These spacers prevent the stem from creating a stress riser on the steerer. Racers must factor in these spacers when sizing their bike.

3. Use only the stem brand and model that came with the bike. This one is a little tougher for most racers as we understand the desire to go lighter, lower or longer with their position. But not all stems will work with carbon steerers. In fact, the lighter the stem, the less chance it will be compatible with a carbon steerer. The maker of the carbon steerer can only assure the compatibility of the stem they spec on the bike. This is reality. Therefore, the only safe approach is to stay with the stem brand that shipped with the steerer.

If racers neglect any of the above, the chances of a carbon steerer tube failure are real. If racers neglect multiple points above, the chances of failure increase exponentially. The Trek rider that brought this matter to your attention installed a very light FSA stem onto his Trek carbon steerer. From our experience, this stem is not compatible with any carbon steerer from Trek and most likely any carbon steerer from any bike company. The racer also admitted ‘tightening down’ his stem bolts for a recent gravel race, most likely over torquing the stem clamp.

Trek has been proactive in this matter. We notified all of our dealers last fall with a service bulletin warning of the above compatibility and installation issues. These warnings are also covered in our owners manual and on our website. We have also recently notified the Consumer Product Safety Commission of the compatibility conflict with aftermarket stems and carbon steerers and are waiting for their direction on next steps.

While the weight of racing cycles has dropped dramatically in the last few years, the necessary attention to proper installation and compatibility has increased. Manufacturers have recently introduced more and more proprietary parts because this is the only way to ensure proper compatibility between super light pieces. Changing any part from the original spec can be risky and potentially hazardous. Velonews readers should look at their current set up and make sure that they are following the 3 rules of carbon steerer installation noted above. If they have not followed the rules, the only safe course of action is to replace the fork. We know this sounds extreme but damage to carbon can be tough to see and the importance of the steerer tube integrity is not to be taken lightly.

Thanks Zack- the more your readers know, the less chance of future problems on the road.

-Dean Gore
Trek Global Director of Marketing
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