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I've been running a non-brand name full carbon saddle for less than a year. It lasted through a couple of crashes and 'cross season. But when my usual ride stopped for coffee, I found out both rails failed. When in alignment, the saddle held enough to get me home.

The break was right at the point where the Thomson Masterpiece clamp mechanism starts, not far behind the nose of the saddle. Is there anything to be aware of about where the rails broke? The seatpost is offset - does this mean I should be running a seatpost without an offset?

I expected the failure at some point, just want to be sure there isn't anything I'm missing before shopping for a replacement.

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  • Saddle rails can fail. I've seen it on exercise bikes at our gym, which is not exactly a "punishing" environment. What's often not appreciated is that the rails are hollow tubes, not solid bars, and thus they can fatigue fairly easily, especially if overloaded.
    – Daniel R Hicks
    Commented Feb 11, 2013 at 23:03

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The first issue with carbon rail seat posts is the lack of a standard for rail diameters. This often leads to the seat post clamp being improperly sized when compared to the saddle rail.

Due to the stress riser of a seat post clamp on carbon, an ill fitting seat post clamp can contribute un-necessary stress to the carbon rails.

Carbon is much more likely to develop stress fractures due to over tension of a seat post clamp\stem clamp\etc than aluminum or steel. Because of this, and the above situation, proper tension of the seat post clamp (along with an anti friction paste) is paramount.

Personally I don't think standard carbon rail seat posts are worth the hassle (of fitting them propertly, tensioning them properly, etc) of saving 20-40 grams. Double so if you are doing any type of off road riding (like cross) where the external forces at play are magnified.

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  • There are other advantages beside the weight that make them beneficial. I have 3 or 4 old saddles of varying brands that have bent (slow deformation) metal rails which cause the saddle surface to no longer be flat. I finally gave up three years ago and switched all my saddle to carbon rail models. I had to change several seatposts to make sure the clamping mechanism was compatible. That being done, three years later, none of my carbon rails are bent, and none have failed.
    – Deleted User
    Commented Nov 19, 2014 at 19:41

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