Well, any "sharp" edges on stems should really be removed if you're using them on a carbon steerer, because yes, they could very well "mark" up the steertube, and if they score it, could create a very dangerous stress riser and that's what the Bianchi warning is concenred about. Consdier the force when you are braking and a lot of your weight is on the bars. That force would like to snap that steertube right at the base of the stem, or the upper headset bearing. Without the underlying support in that area that the expander plug provides, the lower edge of the stem can certainly want to gouge into the front of the steertube where it meets at the lower lip. With the plug in there, you could still potentially overtighten the stem and gouge the steertube a bit (hopefully you don't), but the added support will go a long ways towards preventing it from actually snapping at that point. And again, depends on how the whole thing is designed... some, like Canyon as you mention, do not even have a plug in there. But the C59's absolutely do, a very long one.wilwil wrote: ↑Wed May 16, 2018 3:50 pmI understand that, but how deep the plug goes won't effect cut marks happening on the outside face of the steerer as mentioned in the Bianchi warning. I have seen such marks and put it down to over sharp edges on stem or spacers.Calnago wrote: ↑Wed May 16, 2018 3:31 pmIt goes back to what was being said earlier... and relates to where the interenal expansion plug ends up being. In lots of cases the expansion plug is quite short and is designed to be positioned in a very specific spot within the steertube, and most typically wants to support the lower bolt area and the lower edge of the stem where it meets the steertube. If you throw too many spacers above the steertube that means the expansion plug also is positioned higher (also depends on the plugs design as well). This it may provide an anchor to provide the preload on the headset still, but it no longer is providing the structural support that it is intended to provide. And every system is different these days, some don’t even use an extremely an expansion plug. Best advice if you’re not sure is to follow the manufacturers recommendations.wilwil wrote:Why would a possible wear or cut mark from the lower edge of the stem only be there if the stem had had spacers of more than 5mm above it?Cemicar wrote: ↑Sun May 13, 2018 11:20 amI think this has been suggested by bike manufactures, besides stem suppliers such as Deda.
Here is what Bianchi said for instance.
https://www.bianchi.com/global/news/new ... ty-warning
Cutting the steerer as short as possible makes the frame much harder to sell or adjust if you need to change your position. I usually have 10-15mm spacer above and make sure the bung is deep enough. Doesn't look as nice though. Canyons and C59s came with Acoss headsets that have no bung.
If you want to leave a bunch of steertube on top for resale purposes, well that's a different thing. Just make sure if the bung is intended to be in a certain place that it ends up in that place regardless of how big a knob you want to leave on top. But really... I think anything more than a centimeter starts looking really hideous, unless you're still in the process of deciding where you want it to be cut. I guess I don't worry about setting up a bike for the next "potential" owner, but to each his own.