Canyon Bicycles Warranty Failure: Undersized, Oversized

When a £3,000 carbon bike goes wrong, you would expect the manufacturer to stand behind it. That was not the case here. This Canyon Ultimate CF SLX arrived after Canyon refused a warranty claim. The owner had gone through several bottom brackets in just a couple of years and on the last replacement spotted a serious fault. He sent it to Canyon under warranty. They refused, blaming “poor maintenance,” and returned the bike. What we found tells a very different story.

The bike is a Canyon Ultimate CF SLX, disc brake model in size 2XL. The customer wanted a new bottom bracket fitted. Before fitting anything, I checked the frame tolerances. That is when the issues started to appear. On the non drive side both the go and no go gauges fitted, which should never happen. The hole was significantly oversize. On the drive side the no go gauge did not fit, but the go gauge only entered partway. On closer inspection the bore was tapered and oval. This level of variation is not acceptable in a high end carbon frame.

Using a three point bore micrometer, it was obvious the hole was not round. Rotating the instrument showed tight and loose spots as it locked and freed. This confirmed ovalisation and tapering. Measurements showed the bore size around 40.94 mm, but with variations that suggest shrinkage and local distortion. Carbon should not leave you with this kind of inconsistency if manufactured correctly.

The most serious finding was a crack. The paintwork was visibly bubbled. Inside the frame, with the cable guide removed, a white line was visible along the joint. The crack ran across the bottom bracket area where material was already weak due to the cable routing. This was not just cosmetic, it was a structural failure. Carbon fibre is strong in tension but weak in compression. At the undersized bore, high compressive stress had built up. With the thin cross section around the cable guide, the fibres buckled, resulting in a crack.

The problem is not the crack itself but what caused it. The bottom bracket was heavily undersized on one side and oversize on the other. On the oversize side, the bottom bracket pressed in with no resistance. On the undersize side, the interference fit was extreme, generating excessive stress. That stress concentrated at the weakest point, the thin section near the cable guide, and caused the fibres to fail in compression. This is a manufacturing defect, not poor maintenance.

Canyon refused the warranty on the basis of improper maintenance. That defence does not stand up to technical scrutiny. Plastic bottom brackets wear faster than carbon frames. If wear had occurred, the plastic should have deformed, not the frame. The level of ovalisation and taper present points to defective manufacture, a bottom bracket cannot shrink to become undersized over time. The crack was present when Canyon inspected the bike, yet they did not notify the customer. The tolerance stack up here is poor. Even if Canyon argue the frame was technically within THEIR tolerance, sound engineering judgement says otherwise.

The scandal is not just the defect but Canyon’s response. They sent a cracked frame back to a customer, denied warranty, and did not inform him of the structural failure. Had he continued to ride it at high speed the crack could have propagated, leading to catastrophic failure and potential injury. Canyon may have saved themselves a warranty replacement, but they have left a customer with a dangerous, unusable frame and raised serious questions about their engineering and ethics.

Under UK law, a consumer has the right to remedial action if they can prove a defect existed at the time of purchase. This right is time limited to 6 years. The burden of proof lies with the customer, who must show on the balance of probabilities that the defect was present at purchase. In this case, the undersized bottom bracket bore is clear evidence of a manufacturing defect and would provide grounds for remedial action. The oversized side is less clear, as it could theoretically have enlarged through use, but this is unlikely given the absence of fibre fraying and the extent of oversize.

More failures…

Following the publication of this article and the YouTube videos. A Hambini Viewer emailed in with photographs showing a similar failure mode – undersized BB and crack emanating from the same point on their Canyon. Canyon denied their warranty as well.

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