Frames that suddenly break without a collision or a fall. Bikes which have been ridden over very short distances and that have given way without reason. Yet the reason – or rather, the reasons – are there, even if they are not always obvious.
The memory of carbon fibers
The carbon tubes that constitute a frame are made up of multiple layers. This can create a discrepancy between the surface layers and the inner layers. On the one hand, the percentage of manufacturing mistakes regarding the innermost parts of the fibers is really very low, given they are thoroughly checked with cameras and other visualization systems; on the other, perhaps a collision that occurred in the past may have damaged the innermost parts of the carbon leaving the outer layers intact – and therefore aesthetically problem-free.
By collision we do not only mean an accident against another vehicle, but also a fall or even riding over a rather deep pothole. We cannot know for sure what triggers the breakage. In the past we have repaired frames that, once cut and opened, were seen to be joined only by very few fiber bundles, although externally they did not reveal anything unusual. So if you think that your bike has suffered a trauma, better have it checked by a frame manufacturer. The carbon breakage can be hidden inside.
The wrong size
Unfortunately, due to the fact that many people do not rely on expert advice and are often misinformed in their research, they end up purchasing bicycles that are clearly smaller than their size. Despite the power of information on the internet, this problem shows no sign of diminishing, on the contrary it has increased. Therefore we often see many breakages in the vertical tube caused by a seat tube that has been pulled out excessively from the frame. Moreover, the uneven weight balance caused by the wrong bike size causes the breakage to occur with no apparent warning in the middle of the frame, in the down tube or top tube. In reality, the reason that causes this breakage is the distribution of the masses that creates excessive effort in only a few points.
Let’s be realistic: a lighter bike will obviously be more performing, but it is equally clear that the weight is given by the sum of the bike plus the cyclist. If the cyclist is not light, it will not be possible for a light bike to sustain a consistent mass. It takes proportion, it takes common sense, it takes realism. The same goes for very tall people. Longer tube = more lever, greater stress. For a person over 1.90m a slightly heavier but more robust frame needs to be taken into consideration.
A key factor regarding the lifespan of a frame and a possible carbon breakage is who uses it and how it is used. Under 23 riders who cover 35,000 km per year, will change 3 saddles, 3 chains and a sprocket set every season; their frame will still be valid at the end of the year although inevitably worn down. It is a question of both kilometres and power: the “Sunday cyclist” who occasionally develops 280 watts in a 15 minute climb, is not to be compared to the competitor who develops perhaps 350 watts over stretches of 20 minute laps which are repeated 3 or 4 times during a single bike ride. It’s like taking a car chassis and mounting a 70 Kw or 200 Kw engine on it. The stress will be very different and will be seen in the long run.
We will never tire of saying that the carbon processed in Italy has extremely high quality standards. Carbon fiber can have many weaves; different resistance and torsion characteristics can be obtained for the same weight according to how carbon fibers are weaved and how they are processed. Among the frames that we have repaired belonging to other brands, we often find that one of the rear stays is broken. The tubes here are very small but stressed because they need to withstand the turning of the rear wheel. The quality of the fiber here is fundamental, because the tube size cannot compensate for a deficiency in the structure.