Originally Posted by
rosefarts
It seems that no matter how tight the stem is, the steerer is slick enough to gradually loosen.
I had a bike with no compression plug and would put a piece of threaded rod in and tighten, then remove. I'd get 3 or so rides before needing to do it again. This was back when carbon forks had aluminum crowns so you could do this. It would have crushed the steerer to make it any tighter.
Once I got a proper plug, it never came loose again.
Also, a proper plug for a carbon steerer resists crushing force from the stem. It makes the whole system stronger/safer.
Steel and aluminum aren't so particular.
the plug maintains the diameter of the rather flexible CF/epoxy material, allowing the clamping force to remain consistent.
the cracks happen when the epoxy is flexed or stretched beyond it's yield point.
carbon fiber material has an amazing Tensile strength, less compression strength, and not much resistance to flexing.
the epoxy resists flexing far better, but is still lacking, compared to most metals.
the cf and epoxy are both far lighter than metals, so they can be made thicker, and still be lighter than metals.
seat stays were the most common fail point of CF frames in recent years.. they are under compression and flexing loads, and are much thicker tubes now.
the original CF frame fails were at flexed joints.. now those joints are wrapped with extra materials, but the central portions of main tubes under tension can then be thinner..
recently improved vacuum and compression of the epoxy/cf during the curing makes the materials more consistent, and stronger too.
trade offs.
and the aluminum plugs add enough weight to negate any gain from using a CF steerer, instead of aluminum, from what i've found....