Kimmo 

...For a crash course in poxy expander plugs, examine any plug that tries to get clamping and preload done with a single fastener. Every such I've seen was a joke.

Seattle Forrest

Nobody thinks a product will be perfect in every way because an engineer built it. People think reputable companies don't use designs that get their customers killed.

Kimmo 

And it appears that a compression plug doesn't have to adequately do what it says on the tin to prevent that.

However, I for one will continue to prefer a well-designed plug, particularly given that I don't poke my steerers through the stem.

eduskator

What I'm saying is that CF components have been around for as long as I can remember (a few decades?), and with all the R&D that's going on, if this would have been an issue, it would have been looked at & solved by now. If your freaking bike is built with a full, half, cucumber shaped or no compression plug at all, it's not a coincidence - it's intentional.

If your feel reassured using an aftermarket plug that, according to you or a youtube wizz, supports better the stem bolt's pressure on your fork tube, then be my guess! I would like to see a resistance test between a factory setup on a specific bike versus an aftermarket plug on that same bike that's longer and see which one is tougher.

terrymorse 

To your mind, turning the top cap to provide preload sucks.

But since preload is a low force, turning the top cap against the top of the stem to produce that small preload seems to be a reasonable design.

Regarding your other complaints, those claimed problems are not evident from the drawing.

redlude97

In practice they work fine for setting pretension, not sure how the top cap spinning against the stem or a spacer would affect being able to set it. You set the compression ring portion so it supports the bottom stem pinch bolt, and the top cap supports the top bolt portion of the steerer tube. Sure there are other designs I prefer but it doesn't mean they suck if they fit properly.

eduskator

^^ and WORK properly, because you know, that's the main objective of a component (having a purpose and doing it correctly).

Mine works just fine. Whenever I feel a slack in my headset, all I need is to loosen the 2 stem bolts, turn the top cap screw clockwise until everything is snug, and then tight back the stem bolts to the recommended torque. Voilà! Could it be simpler?

redlude97

While I do agree that a properly built steerer tube set up with a properly torqued stem shouldn't really need reinforcement, the engineering spec'd tolerances and build quality to spec don't always match, so a good compression plug adds to the safety margin of preventing cracks in the steerer tube and also possibly preventing catastrophic failure if the steerer does crack. This mostly has to due with the imperfect nature of carbon manufacturing, and the nature of tolerances and torque spec ranges means there is always going to be some variability in the resulting fit of all the pieces together

redlude97

You should ask yourself why it is developing slack in the first place and the implications if you didn't notice to address that. A properly tensioned headset shouldn't loosen, and would indicate another issue

eduskator

Can't tell if it's developping anything for now since I bought the bike used. It's definitively on my radar though. Moreover, the previous owner didn't seem to know what he was doing at all. Anyways, I checked everything the day I got it & made necessary adjustments. I think the stem bolts weren't tighten properly.

dddd

I've seen headsets where the wedge ring in the top bearing had seemed to have lost it's ability to maintain a tight fit between the steerer and the bearing.

And I've seen bikes where the bearings had developed radial play between the bearings and the cups or seats.

Often the top cap is found to be bottoming on the end of the steerer, sometimes related to the above two sources of wear, making headset tensioning impossible.

I think that Cervleo's (and other's) use of the bonded-in metal tube that extends from below the top bearing to the end of the tube is inherently the most fool-proof, since you can cut down the steerer and only have to worry about pushing the star nut in further. But I did see one case (yeasterday) of the star nut's threaded center becoming free-spinning in the star nut itself, which seems tricky to correct since star nuts can't be removed.

I like top caps which center on the OD of the steer tube using a short length of integral spacer, instead of imposing dead space inside the very end of the steerer (which might have a stem clamped on at this very location).
There will always be situations where users might want to raise their stem some bit above the end of the steerer, and the stepped top caps made this perfectly normal back in the days when many bikes came with zero spacers atop the stem, and with a deep step-down on the bottom of the cap (a situation which did gradually go away around the time that carbon steerers hit the scene).
I notice that some of today's expander plugs do a poor job of having their gripping supports extend near to the end of the steerer, possibly to give them a bit more wedging travel to accomodate the largest ID's of metal steerers.

We as customers have no data as to which stems impose the most concentrated clamping loads, so it's buyer beware when choosing a stem maker. It's not just the sharp edges but also the flexing of the ears as the bolts are tightened, and of course this can also affect handlebar clamping. It's no surprise then that handlebar and stem makers suggest use of same-brand parts, since testing everybody else's parts would be an endless task. The fork steerer however is usually not from the same vendor as the stem, so there would seem to a need here for a higher factor of safety that a full-length tubular insert (or a thicker top half of the steerer) provides.

eduskator

Yes - if I hadn't been able to achieve a snug fit, I would have checked the length of the steerer tube. Fortunately, I only had to tighten the top cap screw 1/4 of a turn to remove the slack. If it becomes slack again soon, I'll dismantle the stem, remove the forks & inspect the head set.

jadocs

This is no different in function. You still need 2-3mm of space to properly adjust the headset. The cap does not sit flush with the top of the steerer. The difference between this and the others is the top cap has a sleeve that goes inside the steerer providing reinforcement vs the other expanders that have a lip that sits on top of the steerer.

eduskator

Indeed. 3mm is what's recommended. Should look like that (without the star nut, of course...):



Now, if you cut it properly to achieve that space between the top of the stem & end of the fork tube and you end up with the top cap sitting directly on the fork tube a few months later, you have a bigger issue that should be looked into ASAP.

superdex

This. Because there's too many spacers. Lower the stem by removing the spacers, and flip it the other way. Boom best of all worlds.

superdex

Like the one from ENVE? (unless I'm misunderstanding your statement. This is what I have in my fork atm, and it works just great)

https://vimeo.com/120504198

https://www.enve.com/en/products/fork-compression-plug/

Kimmo 

No, I imagine one made by ENVE would probably work.

It's a bit of a tall order, though... It has to somehow tighten the wedges before applying preload. Must be a neat part.

Kimmo 

Rivnut tool?

noodle soup

Wilmingtech

I posted this over at WW. Take it for what its worth.

I recently chopped the steerer tube of my 2 carbon framed bikes to get the front end dialed in.

Before this I had never chopped a carbon steerer before and some recent threads had encouraged me to do a little bit of research on cutting the steerer and the proper use of expander/compression plugs in a carbon steerer. I couldn't find a whole lot of detail online (even parks website is vague) so I have compiled what I was able to find through conversations with other bike mechanics and online information. I started this thread to give back a little of what I have picked up along the way and let you guys (and girls) do what you want with the information. Feel free to add, change or update any information as you see fit.

The 2 bikes I have for reference are a 2013 Ridley Helium and a 2017 Blue Competition Prosecco. These both have standard threadless Carbon steer tubes with 2 piece stem and handlebars. Here is the collection of expander plugs I have had to work with -



The Ridley expander plug is a 6cm dual sleeved plug. It has 2 very thin alloy sleeves, one slides into the other to evenly distribute the force of the compression plug against the steerer tube.


The plug that came on my Blue Competition is a common style plug used in many carbon bikes these days. Typically shorter than the stem clamps. From what I have read, this type of compression fitting doesn't allow for spacers above the stem as it raises the compression plug above the bottom stem clamp. It is designed to specifically protect the top of the steerer tube from being crushed by the stem clamp


The Deda plug is one that I bought to replace the plug on my Blue Competition bike. It is 4.5 cm long. It is similar to the Ridley exapnder except that it has a single sleeve that is thicker than the 2 sleeves used on the Ridley expander.


There are (3) main purposes for the expander plug (aka compression plug, headset plug, headset compressor plug).


1. The first function of the expander tube is to be able to pre-load the headset before clamping on the stem.

By placing the expander plug in the steerer tube and leaving a 2-4mm gap between the top of the expander plug/steer tube and the top of the stem (or small spacer) it allows the pressure of the stem cap pushing down on the stem (or small spacer) to pull up the fork/steer tube tightening the headset from the bottom of the fork steer tube and pushing down on the stem to tighten the headset from the top. (see diagram)



2. The second is to reinforce the contact area on the steer tube that the stem clamps around.

One of the two mechanics I spoke to said that stem replacement is easy for any cyclist yet most don't use a torque wrench of any kind nor do they understand the expander plug. The expander plug reinforces the area the stem clamps to and prevents damage to the layers of the carbon fiber (Fiber layers can also loosen over time especially with repeated tightening and loosening of the stem clamp). The other thing that was mentioned was the collapse of the top of the steerer tube either from too many spacers on top (Raising the expander plug higher than the stem clamp) or over tightening or wear of the tube from the bottom stem clamp that has no expander reinforcing it.

This image shows how spacers on top of the stem could negate the effectiveness of the expander plug



3. The last is to reinforce the steerer tube against the pressure of the riders weight up and down on the handlebars and stem


I asked a local bike mechanic about this. He explained it in this way - Take a paper towel tube, think of it as a steerer tube, hold it 1/2 way up and then take your other hand and put some pressure on the very top of the tube and take a look at where the paper tube starts to give way. Take 2 more paper towel tubes except this time insert one inside the other. Then do the same thing as above and you will see that the paper tube for the most part holds up for a little longer than the single tube by itself. The expander plug serves the same functionality. It takes the pressure applied to the steerer tube from the stem clamp and helps to evenly distribute that pressure across the inside of the steer tube. While the carbon tube itself is probably strong enough to hold up to most forces placed upon it, the expander tube increases the strength of that tube over the life of the bike. It's repetitive forces over time that wear away at the steerer tube. (He said picture a 250lb guy on a 17lb bike bunny hopping off a 8" curb with a 13" stem and landing with most of his weight on the handlebars)

Here is an image showing the short expander plug that came with the Blue


And here is an image showing the Deda plug replacing it for better reinforcement of the steered tube



The most common types of damage to the steer tube come from incorrect torque specs on the stem pinch bolts. Suprisingly just as often from being not tight enough. The movement from the stem not being tight cuts into the steer tube. The other common type of damage comes from a seized up headset bearing that is not turning with the steer tube and cuts into it.

All that being said along with the number of recent posts on steer tube failures, take the time to check your steer tube, stem clamps and handlebars and make sure your expander plug is doing its job.

-Sean

Kimmo 

Depending on how finely you want to fettle your machine, this can be reduced to as little as 0.5mm, which would be advisable if you want no spacers above your stem. If so, it's also a good move to modify the top cap to minimise or eliminate any of it that prevents the plug from being mounted as high as possible.

Wilmingtech

The gap is there to take up any slack between the steer tube and top cap when pre-loading the headset.

While the final gap between the top cap and steer tube can certainly be one half a millimeter, I find it highly unlikely that you would be able to get enough load on the headset with that tiny bit of adjustment.

Do keep in mind that spacers are not necessary as this gap can be spaced with the inside wall of the stem slightly above the steer tube.

Just make sure your cut on the steer tube is accurate. It's always possible to trim off a little more but impossible to add once its cut.

-Sean

eduskator

This ^^. Not leaving enough space might result in the need to remove one of the spacers if you can't get enough load on the headset. Every bike is different thought, but I'd stick with at least 2-3mm.

Kimmo 

I'm talking about the final gap. Fettling is how you get there - you know, patience, care, trial fitting, etc.

I also like to countersink the top of the steerer tube and bevel the top of the expander plug so it sits flush in the top of the steerer. This might be controversial, but at least it gets some of the steerer right up to the top.

Seattle Forrest

Are we talking about road bikes here, or BMX?