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Explain Like I'm 5: Don't I need a compression plug to oppose the stem bolt forces?

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Explain Like I'm 5: Don't I need a compression plug to oppose the stem bolt forces?

Old 09-20-19, 01:18 PM
  #26  
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Originally Posted by Newspaper_Nick View Post
Is this something that replaces star nuts?
My understanding is that star nuts are ok for metal/alloy steerer tubes but no bueno for crabon fiber steerer tubes. Again, I believe this is "conventional wisdom" but have zero "proof." It does make sense because a star nut would possibly cut into carbon while the expansion plug won't.
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Old 09-20-19, 01:45 PM
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Originally Posted by redlude97 View Post
Thanks for the video. He did demonstrate how the expansion plug does deform the steerer tube, but that's not really proof that the cap/plug is necessary once the preload is set.
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Old 09-20-19, 02:17 PM
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Aluminum liner tubes, expander wedges and bolts... are we going to be back on quill stems eventually?
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Old 09-20-19, 02:37 PM
  #29  
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Originally Posted by MoAlpha View Post
I confess to this form of weenie anxiety too. My Cervélo came with only a star nut.
The Cervelos have an aluminum liner glued into the steerer to hold the star nut and support the carbon tube. No need for the expander plug.
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Old 09-20-19, 02:51 PM
  #30  
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If I did that the answer would be something like I'm sure that your father has taken care of that.
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Old 09-20-19, 03:33 PM
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Originally Posted by ingo View Post
The Cervelos have an aluminum liner glued into the steerer to hold the star nut and support the carbon tube. No need for the expander plug.
Thank you!
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Old 09-20-19, 06:36 PM
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Originally Posted by Seattle Forrest View Post
This forum is older than spell check, which gave us asploding frames from massive guads.
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Not to mention droped hamers.
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Old 09-20-19, 06:40 PM
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Old 09-20-19, 07:43 PM
  #34  
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I'm guessing a crabon tube that maybe needs a compression plug is heavier than an alooooominum tube with a star nut.

For years I ran a MTB without a top cap or star nut because the steerer tube was stuffed with lighting electronics. Yes, it is perfectly safe, but not idiot proof so maybe the 41 shouldn't go there.
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Old 09-20-19, 08:17 PM
  #35  
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Originally Posted by redlude97 View Post
the top cap used with those types of carbon steerer compression tubes prevent the tube from deforming on the open end where cracking generally occurs, it is necessary for proper function of the compression plug design
No the top cap does not sit flush on top of the steerer. In the video you posted the guy is talking about compression plugs which have a lip that sits on top of the steerer. The cap needs 2-3mm of space to compress the headset to spec. He was just demonstrating how the compression fitting can expand the steerer. He just happened to have the top cap attached in the demo. If it were on the bike there would be 2-3mm of space in order to adjust the headset.

Last edited by jadocs; 09-20-19 at 08:23 PM.
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Old 09-20-19, 09:24 PM
  #36  
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Originally Posted by Seattle Forrest View Post
People have a lot of anxiety about this.

The handlebars and seat tube don't have compression plugs in them, and nobody seems to mind.
Your bars and seatpost aren't clamped on the end of the tube. Haven't you seen carbon bars deformed where the stem clamps them?
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Old 09-21-19, 08:18 AM
  #37  
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Originally Posted by jadocs View Post



No the top cap does not sit flush on top of the steerer. In the video you posted the guy is talking about compression plugs which have a lip that sits on top of the steerer. The cap needs 2-3mm of space to compress the headset to spec. He was just demonstrating how the compression fitting can expand the steerer. He just happened to have the top cap attached in the demo. If it were on the bike there would be 2-3mm of space in order to adjust the headset.
I'm talking about this type that is referenced in the video. The top cap need to fit tightly in the steerer tube
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Old 09-21-19, 01:07 PM
  #38  
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Gotcha
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Old 09-21-19, 01:56 PM
  #39  
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Originally Posted by ThermionicScott View Post
Aluminum liner tubes, expander wedges and bolts... are we going to be back on quill stems eventually?
As an example, having used computers since TRS-80, I'd say probably.
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Old 09-21-19, 02:38 PM
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Originally Posted by Kimmo View Post
Your bars and seatpost aren't clamped on the end of the tube. Haven't you seen carbon bars deformed where the stem clamps them?
The guy that made the video is wanker. He knows what he’s talking about, but he’s marketing a product that he created, to help prevent an issue that isn’t really an issue.
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Old 09-21-19, 06:12 PM
  #41  
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I especially like how he totally glossed over the importance of getting the top bolt tension correct.
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Old 09-21-19, 11:29 PM
  #42  
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Originally Posted by noodle soup View Post
The guy that made the video is wanker. He knows what he’s talking about, but he’s marketing a product that he created, to help prevent an issue that isn’t really an issue.
I just hope that's only his ID. Sounds a bit cruel to him.
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Old 09-22-19, 03:13 PM
  #43  
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Originally Posted by datlas View Post
Thanks for the video. He did demonstrate how the expansion plug does deform the steerer tube, but that's not really proof that the cap/plug is necessary once the preload is set.
Yup.
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Old 09-22-19, 03:26 PM
  #44  
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Originally Posted by redlude97 View Post
Funny how this guy says that many manufacturer did not engineer well their factory compression plugs & finds flaws in them (IE, says that Giant should have opted for a straight plug instead). I mean, if the damn product was developed and engineered in a specific way (including shape), I'm confident it's pretty much doing what it should be doing.

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Old 09-22-19, 06:35 PM
  #45  
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Regarding the need for a compression plug to support the steerer tube. I owned a Colnago C59 which used a wedge type headset which eliminated the need for a top cap to set the preload. Just mounted the stem a flush as possible and the set preload at the headset.

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Old 09-22-19, 09:30 PM
  #46  
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Originally Posted by noodle soup View Post
The guy that made the video is wanker. He knows what he’s talking about, but he’s marketing a product that he created, to help prevent an issue that isn’t really an issue.
Not sure what vid you're referring to; my comment about clamping a tube on the end isn't based on anything but the 5mm spacer and steerer poking out of the stem rule.

FWIW, none of my carbon steerers poke out of the stem, but I ensure my compression plugs are a good design and are set up properly, and the bottom bolt on my stems is tighter than the top. Seems prudent to remember we're dealing with fibre reinforced plastic...

Originally Posted by eduskator View Post
Funny how this guy says that many manufacturer did not engineer well their factory compression plugs & finds flaws in them (IE, says that Giant should have opted for a straight plug instead). I mean, if the damn product was developed and engineered in a specific way (including shape), I'm confident it's pretty much doing what it should be doing.
'Fraid not... you'd think the threat of folks lawyering up after smashing their teeth out might spur some competent design, but there's a lot of rubbish out there. Like this:



That one's utter crap, and there are worse than that.

I guess the risk of your stem popping off your carbon steerer must be pretty minimal if Darwin has allowed these poxy units to continue to be a thing... I like to sail pretty close to the wind, but this is a risk I'm going to mitigate, albeit to less of an extent than the accepted wisdom.

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Old 09-22-19, 10:05 PM
  #47  
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Originally Posted by Kimmo View Post
... you'd think the threat of folks lawyering up after smashing their teeth out might spur some competent design, but there's a lot of rubbish out there. Like this:



That one's utter crap, and there are worse than that.
Nonsense. The only rubbish here is your unsubstantiated statement claiming there is something wrong with this steering tube-compression plug design.

There isn't. Stop perpetuating a myth.
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Old 09-22-19, 10:14 PM
  #48  
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Originally Posted by terrymorse View Post
Nonsense. The only rubbish here is your unsubstantiated statement claiming there is something wrong with this steering tube-compression plug design.

There isn't. Stop perpetuating a myth.
You know these plugs, then? And have experience with a range of plugs as a basis for comparison?

Some are so bad they struggle to grip enough to preload the bearings, let alone support the steerer internally (the necessity of which is apparently a matter of controversy), others don't stand a chance of performing the latter despite managing the former, and the one pictured above manages to introduce a new degree of crapness by trying to be clever and integrating the top cap, which turns against the stem as you're preloading the headset, which is plain nasty, and makes it a fiddly hassle for no good reason. The rest of its design is equally nasty.

It's crap, and if you insist on disagreeing, I submit that you lack the discernment to perceive that.

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Old 09-22-19, 10:27 PM
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Originally Posted by Kimmo View Post
You know these plugs, then?
I can read a drawing, and there appears to be nothing wrong with the design depicted in the drawing. It looks like so many other designs from so many other manufacturers.

Point to the place in the drawing that shows the claimed design flaw in this compression plug that prevents it from providing a bearing pre-load.
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Old 09-22-19, 11:38 PM
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I never said this plug in particular couldn't do that; I said it was crap in its own special way - if you can read a drawing you might be able to see the problem. Unlike plugs from other companies, the top cap is the tension bolt, which in practice, sucks.

Also, from memory, the tapers are a bad angle and it needs to be lubed (something I always do but is otherwise rare) to work at all, and the short length that bears on the inside of the steerer is badly placed; too low IIRC.

I'm reminded of a whole bunch of undercooked me-too internal cable routing in frames that I've come across, which only passed muster because you can't see it. The assumption that a big company employing qualified engineers will necessarily make parts that a bloke on the street couldn't find problems with, is false.

Whether compression plugs have one job that matters or two is a matter of debate. Whether some are absolute crap shouldn't be. I've even seen a rubber sandwich!

Last edited by Kimmo; 09-22-19 at 11:47 PM.
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