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Carbon Fork Steerer Question

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Carbon Fork Steerer Question

Old 02-13-24, 12:34 PM
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Originally Posted by terrymorse
I'm saying that compression plugs were not intended to solve this "problem".

The whole "compression plugs protect fragile carbon steering tubes from being crushed by mean old stem clamps" story was something people made up, long after compression plugs were introduced. I haven't seen any analysis to back up this claim, and I've been looking for at least 10 years. The story has the sound of bike mechanic scuttlebutt -- plausible sounding, but with no engineering to support it.
I get that they may have initially been produced for another purpose (IE, as a way to preload the headset when ''steel was the deal'' and when alloy was later introduced), and I am no structural engineer, but I am almost certain that CF steerer tubes aren't manufactured to withstand horizontal force / pressure on small areas hence why a compression plug at the right place is a must IMO. I would never clamp down a stem at 8-10nM without a plug pushing against the walls inside to prevent structural damage.

If one of you wants to try it, let me know how it goes! You'll most likely void your warranty, but whatever!
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Old 02-13-24, 12:46 PM
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Originally Posted by eduskator
I get that they may have initially been produced for another purpose (IE, as a way to preload the headset when ''steel was the deal'' and when alloy was later introduced), and I am no structural engineer, but I am almost certain that CF steerer tubes aren't manufactured to withstand horizontal force / pressure on small areas hence why a compression plug at the right place is a must IMO. I would never clamp down a stem at 8-10nM without a plug pushing against the walls inside to prevent structural damage.

If one of you wants to try it, let me know how it goes! You'll most likely void your warranty, but whatever!
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Old 02-13-24, 02:29 PM
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Originally Posted by terrymorse
I'm saying that compression plugs were not intended to solve this "problem".

The whole "compression plugs protect fragile carbon steering tubes from being crushed by mean old stem clamps" story was something people made up, long after compression plugs were introduced. I haven't seen any analysis to back up this claim, and I've been looking for at least 10 years. The story has the sound of bike mechanic scuttlebutt -- plausible sounding, but with no engineering to support it.
Did you review the Cannondale manual supplement I cited above?
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Old 02-13-24, 03:00 PM
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Originally Posted by SoSmellyAir
Did you review the Cannondale manual supplement I cited above?
That's a pretty big manual. I didn't see a reference to compression plug. Can you quote the section?
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Old 02-13-24, 03:47 PM
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Originally Posted by terrymorse
That's a pretty big manual. I didn't see a reference to compression plug. Can you quote the section?
As stated above in post #12:

Originally Posted by SoSmellyAir
See the Owner's Manual Supplement for the Synapse Carbon (2013-2016) at page 8 (Acrobat page 6).

Owner's Manuals - Road (cannondale.com)
With reference to the diagram on the cited page of the cited manual supplement (pasted below), and quoting from paragraph 2 on the same page:


"Adjust the length so that the expander is located at lower stem bolt. The top cap and the expander end provide[] critical support to the carbon steerer when tightening the stem bolts."
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Old 02-13-24, 07:18 PM
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Holy jezuz, I didn't read all that. I'll say this Necco make long expander plugs, one is 4 inches long. That would put the expander all the way past your top bearings.
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Old 02-13-24, 07:43 PM
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Originally Posted by ls01
Holy jezuz, I didn't read all that.
Yay! More work for counsel.
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Old 02-13-24, 07:52 PM
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It’s only 32 words

There’s a bit of Oceangate about the assumption an unsupported CF steerer will be fine under compression.
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Old 02-13-24, 09:16 PM
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Originally Posted by choddo
It’s only 32 words

There’s a bit of Oceangate about the assumption an unsupported CF steerer will be fine under compression.
They have been for years and years.

And they all have the same wall thickness.
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Old 02-13-24, 10:16 PM
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Columbus likewise says that the expansion plug must be installed lined up with the stem clamp in the instructions for their carbon forks:
"CAUTION
In the case of carbon forks, ensure that the contact area between the
internal walls of the steerer tube and the expander matches with the
area where the stem applies pressure to the steerer tube."
https://columbustubi.com/wp-content/...structions.pdf

Last edited by nathand; 02-13-24 at 10:17 PM. Reason: added direct quote of relevant text
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Old 02-13-24, 10:48 PM
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If one were to have an alloy steerer, the default would be to install a star nut, and expander plugs are only common now due to carbon steerers. As such, I’m surprised so many expander plugs (most?) are so short then, and don’t cover the height of a stem, let alone any adjustability.

Dropped bike off at the shop. They’ll start warranty filing once I email them receipts/documentation from Lynskey.
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Old 02-13-24, 10:48 PM
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I see that installation instructions, espeically vis a vis the placement of the stem in relation to the plug has become much more clear and specific than remember seeing with the aftermarket forks i installed 10+ years ago. I happen to - as a total layperson - see sense in lining up the stem clamp with the plug, and I've gone back and made sure it is so for all my CF steertubes, old and new (some of which didn't have the specific instructions).
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Old 02-13-24, 11:23 PM
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Originally Posted by Camilo
I happen to - as a total layperson - see sense in lining up the stem clamp with the plug, and I've gone back and made sure it is so for all my CF steertubes, old and new (some of which didn't have the specific instructions).
Yes, it is common sense, although -- to be fair -- Enve's own online instructions do not specify that the expander plug should be lower enough within the steerer tube to brace against the total height of the stem.

General Fork Installation and Care Instructions – ENVE Support Center Home
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Old 02-13-24, 11:29 PM
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I don't recall the explanation I got from the tech at my local Trek store concerning the expansion plug insertion depth and the potential for crushing the steerer tube. But I did ask him concerning my Trek Domane. The expansion plug is very short, yet the manual allows for up to 40 mm of spacers above the stem. In this configuration, the entire expansion plug is above the stem. The tech said this used to be an issue on some bikes, years ago, but generally is not now and is not for the Domane (and I presume other Trek bikes).

Again I don't remember what he said was the reason it wasn't an issue now. Though it would seem likely it is simply that the steer tube is thick enough. However, all this means is that for some bikes it isn't an issue and for others it is (see the Cannondale reference above).

But if the OP's steerer is crushed, I would think he could feel this by squeezing the tube. Also, if it were crushed, I don't think you'd get the vertical lines he's pointing out. The OP also said they have had more than one stem on there, so perhaps one of them aligns more with those marks. I wonder if they aren't simply from twisting the bars a to align them with the front wheel before tightening the stem to spec. Essentially surfaces scratches.
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Old 02-14-24, 02:34 AM
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Originally Posted by Kontact
They have been for years and years.

And they all have the same wall thickness.
Our friends at Cannondale seem a bit paranoid then?
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Old 02-14-24, 07:08 AM
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Originally Posted by choddo
Our friends at Cannondale seem a bit paranoid then?
The problem is that they can't really control for stupidity. None of these steerers might be a problem if they are used correctly, but none of them are proof against overtightening or using the wrong type of stem. Maybe they found these instructions decrease the amount of knucklehead damage. I don't know - but carbon steerers are nearly 20 years old.
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Old 02-14-24, 07:26 AM
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Originally Posted by SoSmellyAir
Did you review the Cannondale manual supplement I cited above?
He does not seem to care. The guy thinks that compression plugs have no role to play in the steerer tube's structural integrity.

He probably clamps his bike by the top tube on his car rack and bike stand. It's 10x stronger than steel, right?
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Old 02-14-24, 08:08 AM
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There's no obligation to torque the stem bolts to 5 Nm. Torque wrenches can malfunction and cause more problems. Use a short hex wrench and moderate force.

Pictures posted show that expanding plugs are supposed to support the steering tube against clamping force, in addition to allowing the headset bearings to be adjusted and not slip.

I avoid these problems by filling the entire length of the steerer with epoxy, to at least the bottom of the stem. You could go further to the upper headset bearing. A thread insert is placed at the lowest point, so the steering tube can be cut shorter, if needed. Most often, my thread insert is a star nut, ground to a smaller diameter, so it slips easily into the steerer. A long M6 bolt is covered with a plastic drinking straw or heat shrink tubing and screwed into the star nut, to prevent adhesion of the epoxy. Grease the star nut threads too. The steerer is plugged with foam rubber or core foam, just below the star nut. I try to use stem angle to avoid using more than 20mm of spacer above the headset top cover. Two of my bikes have no additional spacer, with -6 stems. On the third, there's a -17 stem and 15mm of steerer that could be cut off.
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Old 02-14-24, 11:05 AM
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Originally Posted by Kontact
The problem is that they can't really control for stupidity. None of these steerers might be a problem if they are used correctly, but none of them are proof against overtightening or using the wrong type of stem. Maybe they found these instructions decrease the amount of knucklehead damage. I don't know - but carbon steerers are nearly 20 years old.
To me, the concern is inconsistency in documentation, as well as margin of error for safety.

I'm reminded of the difference between ibuprofen and acetaminophen (paracetamol to non Americans). It's apparently perfectly safe to take 3x the over-the-counter dosage for ibuprofen - in fact, prescription strength ibuprofen is pretty much 3x strength Advil, and is used as an anti-inflammatory.
Compare that with 3x extra strength Tylenol, which is very, very dangerous, and 4x has been proven to be fatal.

NOTE: DO NOT take my comment above as medical advice - ask your doctor before taking above any recommended dosage on the bottle!!!!

The compressive strength of an alloy steerer can probably withstand multiples of 5nm before crushing.
It seems like the compressive strength of a carbon steerer might not withstand 1.5x the stated 5nm - or even 5nm, for that matter.
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Old 02-14-24, 11:46 AM
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Originally Posted by aliasfox
To me, the concern is inconsistency in documentation, as well as margin of error for safety.

I'm reminded of the difference between ibuprofen and acetaminophen (paracetamol to non Americans). It's apparently perfectly safe to take 3x the over-the-counter dosage for ibuprofen - in fact, prescription strength ibuprofen is pretty much 3x strength Advil, and is used as an anti-inflammatory.
Compare that with 3x extra strength Tylenol, which is very, very dangerous, and 4x has been proven to be fatal.

NOTE: DO NOT take my comment above as medical advice - ask your doctor before taking above any recommended dosage on the bottle!!!!

The compressive strength of an alloy steerer can probably withstand multiples of 5nm before crushing.
It seems like the compressive strength of a carbon steerer might not withstand 1.5x the stated 5nm - or even 5nm, for that matter.
Yet Trek's spacer on top rule was from alloy steerers.
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Old 02-14-24, 12:05 PM
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Good news is that Lynskey was able to send over an email this morning confirming that my bike was sold with an Enve fork, despite it not being on the original invoice. Hopefully it's enough to open discussions about warranty/etc.

Props to Lynskey for having responsive customer service!

I've attached pictures of my older 100mm FSA stem as well. The old stem is an FSA Gossamer, the 110mm that I have on there is an FSA Energy. Bolt configuration is the same between the two, and the stem heights are pretty comparable. Please forgive the tape residue on top; I used to use a phone mount that had a tendency to scratch up my stems (hence tape as a protector).




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Old 02-14-24, 12:09 PM
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Originally Posted by DaveSSS
There's no obligation to torque the stem bolts to 5 Nm. Torque wrenches can malfunction and cause more problems. Use a short hex wrench and moderate force.

Pictures posted show that expanding plugs are supposed to support the steering tube against clamping force, in addition to allowing the headset bearings to be adjusted and not slip.

I avoid these problems by filling the entire length of the steerer with epoxy, to at least the bottom of the stem. You could go further to the upper headset bearing. A thread insert is placed at the lowest point, so the steering tube can be cut shorter, if needed. Most often, my thread insert is a star nut, ground to a smaller diameter, so it slips easily into the steerer. A long M6 bolt is covered with a plastic drinking straw or heat shrink tubing and screwed into the star nut, to prevent adhesion of the epoxy. Grease the star nut threads too. The steerer is plugged with foam rubber or core foam, just below the star nut. I try to use stem angle to avoid using more than 20mm of spacer above the headset top cover. Two of my bikes have no additional spacer, with -6 stems. On the third, there's a -17 stem and 15mm of steerer that could be cut off.
I've been using a small, needle-based torque wrench for the past few years, and recently switched to a Park Tool 5.2. In addition to being much more flexible in terms of usage, it also allows me to validate torque measurements where they need to be validated. At least so far, both tools seem to read 5nm at the same time, so I'm reasonably confident that the tool wasn't the issue.
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Old 02-14-24, 12:18 PM
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Originally Posted by choddo
Our friends at Cannondale seem a bit paranoid then?
​​​​​​​
Originally Posted by eduskator
The guy thinks that compression plugs have no role to play in the steerer tube's structural integrity.
Originally Posted by aliasfox
To me, the concern is inconsistency in documentation, as well as margin of error for safety.
I don't know if Cannondale (and Columbus) are paranoid, but terrymorse 's skepticism does not supercede my common sense and the express instructions in the documentation for my bike.

It is certainly possible that other forks may not need an expander plug that reaches deeper than the bottom bolt of the stem, but I would still use one.
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Old 02-14-24, 02:25 PM
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Originally Posted by aliasfox
It seems like the compressive strength of a carbon steerer might not withstand 1.5x the stated 5nm - or even 5nm, for that matter.
More armchair speculation.
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Old 02-14-24, 03:26 PM
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Originally Posted by terrymorse
More armchair speculation.
My data is admittedly from a sample set of one, but my evidence is in this thread:
- Road bike with carbon steerer, just over 5k miles with the original stem and expander plug
- Aside from a couple of embarrassing instances of falling sideways (not being able to unclip in time, falling over onto the grass), the bike has never been crashed as far as I can recall
- As far as I recall, anytime I adjusted my spacer stack or headset, I used a torque wrench to minimize risk of cranking down much beyond 5nm. Torque wrench reads 5nm, and never pushed to the 6nm mark
- Expander plug was installed snugly, but not to 5nm

And yet, the unsupported portion of the steerer appears to have early stage crush marks. The somewhat supported section above has a surface mark, but not something discernible by touch.

As an analyst, I hesitate to use a single data point and make a generalization, but it seems that this is the likeliest rationale for what I'm seeing.
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