Great Luescher Teknik video on stem selection for CFRP steerer tubes

wafter

Über Member
Location
Oxford
CFRP steerer tubes seem to be one of the areas of a frame most susceptible to catastrophic failure; while also one of the more serious components to fail in terms of the potential outcomes for the rider.

This video gives a really informative and comprehensive overview of how the geometry, position and fitting regime of the stem affects the loads excerted on the steerer tube and in some cases cause damage / promote delamination and failure.


I find this particularly interesting as I did a similar analysis on my Team Carbon last year; finding that the original stem (which looked dirt cheap and had a large aperture in its rear face where it met the steerer) had left some very light witness marks on the steerer tube. As it happens this was replaced with a shorter stem that just happened to have no hole in its rear face so should be a lot kinder to the tube (in the hope that the original stem hasn't already caused any significant damage).

Unfortunately due to the differing mechanical properties of CFRP versus steel it seems a lot of stems that would have been absolutely fine on steel steerers are potentially dangerous on CFRP alternatives; especially when factoring in the importance of fitment position on the tube (proximity to top and internal bung) and the attitude of some people to bolt tightening / use of correct torques.

I've read the odd internet horror story about Boardman Team Carbon steerer tube failure (something that Halfords seem intent on hushing up / sweeping under the carpet) and it makes me wonder to what extent the subjects covered in this video may have played a role in this situation.

Well worth a watch if you run a carbon fibre steerer tube and / or are considering fitting a new stem!
 
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