thatsnotmyname wrote:slowster wrote:If it's basic stuff to you, then you should be able to provide technical references and links to support your assertions. Instead, dismissive comments like "Come on guys, this is basic stuff" and "There you go again, making claims you can’t support" sound like bluff and bluster.
You're asking me to
prove that something which wasn't designed for a particular task, cannot indeed perform that task??? My assertion is that they are not necessary for structural support - only for holding on the top compression cap. I can't find a steerer bung on the market which claims to offer such support. Manufacturers themselves do not seem to claim any such ability for these devices. You'd think if it was such a critical issue, they might mention it. Anyone who disagrees with that needs to be able to explain why. I can't prove a negative.
The steerer bungs themselves are not the component that is at risk of failure or causing damage, and a lot of them are generic items, so it's not surprising that the manufacturers of the bungs themselves do not bother to make such claims: they don't need to. It's more likely that such claims would be made for a branded aftermarket bung, e.g. like
this one ("Extra long 90mm height reinforces carbon steerer tube beneath the stem").
Since the structural function of the bung is to resist distortion and crushing of the carbon fibre as a result of (most likely careless/excessive) tightening of the stem bolts, it's more likely to be the manufacturers of stems, like Deda, and more especially large manufacturers like Trek and Specialized who make complete bikes with their own brand components throughout, who specify how the steerer bung should be installed and stipulate that it should be in the same plane as the stem.
thatsnotmyname wrote:I offered an example of a manufacturer who did not use a steerer bung on a carbon steerer tube in order to underline the point I'm making. Canyon found another way of keeping the headset in compression, so dispensed with the steerer bung. It's not an argument against the wider or legitimate use of steerer bungs, it's simply evidence that one is not necessary to reinforce the steerer tube against clamping forces.
As I said, you cherrypick your sources to support your argument: according to you Canyon doing differently is 'evidence', but guidance from Trek, Specialiazed, Deda and anyone else is just the manufacturer covering their backside against litigation or a 'belt and braces' approach.
Canyon doing differently is not evidence. The history of bicycles is littered with examples of manufacturers who came up with designs which were flawed or dangerous.
thatsnotmyname wrote:thatsnotmyname wrote:Whatever is inside the tube will only 'reinforce' it if it has any structural integrity itself. A split aluminium sleeve which has been expanded to fit the cavity inside does not meet that criteria. Come on guys, this is basic stuff.
slowster wrote:That statement says to me that you are not an engineer.
Well, I never claimed to be an engineer, but feel free to discredit my contention with facts and supporting data, rather than a dismissive ad hominem. Ironically, you accused me of being 'dismissive' earlier.
It's not an ad hominem. With remarks like "Come on guys, this is basic stuff" you've implied that you have significant knowledge and expertise. However, when challenged, you expect others to prove their point, rather than provide evidence why you are right. It's normal for manufacturers to issue instructions on how their components must be used without providing the technical knowledge and test data they have which has led to those guidelines. If you tell people that those guidelines can be ignored, then the onus is on you to provide evidence, not the manufacturers.
I too am not an engineer, but I know that it's not difficult to find examples of a material or component which has little or no structural integrity or strength itself, but which may be very strong when combined with another material or component.
As I understand it the ability of the bung to perform a structural function boils down to whether it exerts an outward (expanding) force on the steerer tube, which I believe it does*, and the extent to which that outward force does or does not make a difference to the steerer tube being crushed, deformed or stressed by (careless/excessive) tightening of the stem. It's probably not going to be possible to give a definitive answer to the latter point without having some very sensitive measuring equiment or testing to destruction. And that's unlikely to happen and the results be put in the public domain unless and until there are some indicators that the current widely recommended practices regarding stem fitting and bungs are inadequate (whereas the reports I've seen so far of failures have probably been due to manufacturers' instructions not being followed). That sort of testing is probably already undertaken by some manufacturers, but they would consider the results commercially confidential, because knowing what and where the failure thresholds are gives them an advantage in knowing how to design cheaper/lighter/stronger parts.
* I've seen at least one report where someone was able to measure a slight increase in the external diameter of a carbon steerer when the bung was tightened.
To be clear, I expect that >95% of the time this issue is probably not critical, because of the margins of safety involved. However, the laws of large numbers probably mean that over time there will be a small number of people who come to grief because they have eroded one, or likely more, of those margins of safety, such as positioning the stem in line with the steerer bung.
