Kimmo

If you think about it, road bikes have as much if not more leverage over the top of the steerer than a BMX, particularly when landing. This is why I consider 31.8 bars to be an overdue development - so many old-school bar/stem interfaces were marginal at best, when it came to landing a bunny hop.

eduskator

So guys, I know this thread is dead (and should stay dead), but I'm flipping my stem today to raise my bars a little & I thought I'd share a few pictures showing my TCR's factory compression plug.

The top of the bolt & the nut at the bottom tightens the plug from the bottom compresses the compression plug (see last picture), stretching the plug to the fork tube wall. It is covering all the length of the stem.






I know, I should probably remove one of the stem spacer to reduce the gap between my fork tube & top of stem. It was cut too short in my opinion.

woodcraft

Yikes. I'll take a star nut & the stem clamped fully on the steerer tube over that.

Dean V

I wouldn't be sure that your TCR steerer has been cut at all. You have a lot of spacers there.
My TCR-SL frame actually came with a light aluminium compression plug that could be glued in to replace the more adjustable, but heavy wedge arrangement.

eduskator

This is what I was thinking as well shortly after posting. There is indeed a good amount of spacers.

eduskator

Seems like Giant's engineers should have asked for your opinion before building one of the most reliable & used bike on the market. It's not like they sell over 5 million bikes each year.

I'll tell them to call you whenever they need advice.

woodcraft

I was yikes-ing that part of the stem is clamping air instead of the steerer tube. I doubt that Giant's engineers would approve of that set up.

eduskator

The stem bolt is actually just a little under the top end of the steerer tube. I was also a concerned, but I measured it & it’s OK.

Fastfwd01

I'm not trying to contradict you personally, but I've always shied away from dropping my bars on my bikes because the Cannondale Owner's Manual actually does specify that (with carbon forks) only their compression assembly is designed to work. I've only very recently been revisiting this topic because I'm now interested in seeing how I like it if I drop the bars on my bikes.

I'm guessing that it would be implied that if you were to drop the bars then you might need to find an alternative, but it appears that they advise against doing so. It looks like they provide instruction for cutting the forks, however. So, you might be correct that they don't recommend a full length compression plug per se.

Bob Dopolina 

No actual data here, however, this was a commonly accepted understanding of the function of the top cap by assemblers.

From handling carbon warranties, in my experience, cracking/splitting/delamination at the top edge of the steerer was responsible for a statistically significant number of failures/claims.

As to the compression plug supporting the steerer and protecting it from the clamping forces, assembly factories (who are guided by the brand they are assembling) also operate on the assumption that it should support the steerer. Whether the person from the brand ACTUALLY checks stuff like this in detail (and not just the paint...) will vary from brand to brand and year to year.

From the warranty side, it wasn't only the clamping forces that contributed to the failures; It was a factor but not the only one.

If you think about all the pieces involved, you actually have a series of points where metal objects come in direct contact with the carbon steerer; There are bearings, the edge of races, compression plugs, the top and bottom edges of the stem, and any top caps and spacers. All of those things flex differently and respond differently to compression and torsional loads.

My point is that sometimes I would see a series of rings on a steerer, not always visible to the naked eye. If there are too many of those or some that are more significant than others that are dealing with opposing forces, it can be enough to cause catastrophic failure in the carbon.

By choosing products that are designed to reduce the chance of 'stress risers' and choosing a compression plug that doesn't add to the potential problem, you can mitigate significant factors that could possibly lead to failure. It's a best practices situation.

Again, no hard data just my opinion based on what I've seen.

Bob Dopolina 

I think you may be drawing the wrong conclusion here. On page 94, in the second section, it seems to imply that they want you to use a compression plug (in a style they like so they provide one) but they are most concerned about end users NOT putting anything in the steerer that has a SHARP EDGE. All the things listed will bite into the inside of the carbon steerer. It seems like this is their biggest concern.