aliasfox

Hi everyone,

There's a bit of play between my centerlock DT240 front hub and my front rotor, and every so often it tricks me into thinking that my headset is loose. I know it shouldn't (I even turn the front wheel sideways to check - nope, no rocking!), but it does. To confirm everything, I disassembled my front end for the first time, cleaned out the grit in there, and put a thin layer of grease on the bearing seats. When I was wiping down the steerer tube, I noticed that the carbon wasn't completely smooth and round, and that there was this 'edge' that shows up, just enough feel with my fingertips, and capture on camera (see photo below).

Am I just looking at the edge of some unfinished carbon, or is this something to be concerned about? It seems perfectly straight and even.



I reassembled the front end, preloaded the headset with my old 6-bolt rotor wheel (no rotational play in that one), and tightened my stem bolts with with my torque wrench (~5nm). This is the only thing that leaves me with a bit of a question.

Thanks everyone!

13ollocks

What’s going on with the steerer at that point? Is that where the stem clamps? (Looks to be too low down, but had to ask). It really looks like the steerer was crushed/compressed on one side of the otherwise normal “seam” that runs down the length of the steerer. I might have said that it was simply a poorly finished seam, but it’s very defined and coincides with a band of discolorization in the steerer. Doesn’t look normal to me.

aliasfox

I’ll have to double check where the stem clamps to the steerer - I don’t remember taking note of that when I reinstalled.


If that ‘seam’ is really a compression-crushed steerer, that’s a bit of a bummer. I’ve tweaked my position a few times:
- Most of my riding has been done on a 100mm stem, with 10mm of spacers below the stem (and 10mm above)
- Swapped the 100mm for a 110mm a few rides ago, same spacer configuration
- Dropped the stem by 5mm after my last ride (15mm on top, 5mm below), and the front end play bugged me enough to disassemble and discover the irregularity.

Understanding the weaknesses of carbon steerers and that the bottom stem bolt is likely below the compression nut inside the steerer, I’ve always used a torque wrench after each adjustment, doing my best not to go past 5nm.

SoSmellyAir

I cannot tell from your photo whether one section of the steerer is crushed. As 13ollocks said, the glossier segment seems to be too low to correspond to your description of your stem setup.

Many regular expander plugs are barely long enough for a regular stem (just under 40 mm height) with a 3-5 mm spacer installed above. I understand that is why excessive steerer length must be cut, i.e., to let the expander plug reach low enough within the steerer and past the lower stem bolt to properly support the stem. Having ridden mostly with a 10 mm spacer above the stem all this time, the compression force exerted by your lower stem bolt may not have been counteracted by the expander plug. Why not try a longer expansion plug? For example:

Specialized Extended Expander Plug For Carbon Steerer Tubes (1-1/8") (Alloy) - Performance Bicycle (performancebike.com)

tomato coupe

It might be that the stem twisted on the steerer, and the white line is just a little bit of resin that's been scraped off the surface.

aliasfox

I think this may be the first time I've heard that 'excess steerer length must be cut,' as I've always read that the top of a carbon steerer tube should stick out slightly (5-10mm) to avoid crimping the top of the tube.

I have no problem getting a longer expander plug if needed, but it sounds like the consensus here is that this probably isn't normal or just some ugly manufacturing, and I should take this bike in for evaluation. Was hoping to avoid dropping ~$1k on a new Enve fork and install - but if that's what it looks like, I'd rather that then broken teeth/collarbone/sternum etc that could come from a failure at-speed...

6thElement

I used the same expander in my recent frameset build that came with an ENVE fork, rather than using the included ENVE plug.

nathand

You want a small amount of excess height - a couple of mm - but you don't want a lot, just enough to hold a short spacer in place. You don't want the steerer to extend further beyond the headset than the maximum height the manufacturer recommends, and you usually want the expansion plug to be centered in the same area of the steerer where the stem is clamped, so unless you have a long extension on the expansion plug you're limited in how much steerer you can leave above the stem.

aliasfox

I guess regardless of whether or not the shop recommends a new fork, I'll see if they have an extended expander plug - the shop I'm taking it to is (unfortunately) a Specialized and Trek shop now, so there's a chance they have what SoSmellyAir shared.

(Unfortunately because they used to carry BMC, Look, Factor, Moots, and Seven before I lived here, and now just carry the big two...)

terrymorse 

I have never accepted this "compression plug must be long enough to cover entire stem clamp" argument.

The compression plus was not intended to provide mechanical support for a carbon steering tube. It was intended to avoid scratching or gouging the inside of the steering tube.

aliasfox

To be honest, this is what I thought, as well - especially as I've seen torque limits on expander plugs as low as 1.6nm. That said, I'll be putting a bunch of pictures into a follow up post that might be useful for this discussion...

SoSmellyAir

Well, that was what I learnt from the manual for my first road bike when I swapped the stem. See the Owner's Manual Supplement for the Synapse Carbon (2013-2016) at page 8 (Acrobat page 6).

Owner's Manuals - Road (cannondale.com)

Is the 1.6 Nm for the top cap or for setting the expander plug within the steerer? The one for my Synapse is 6 Nm, and the one for my Stigmata says 8 Nm.

aliasfox

Took some pictures of the Lynskey after my ride today - I think I'll be taking the Bianchi out this week exclusively, at least until this gets resolved to my comfort.

Here's the bike in question: no, not quite Hot or Not material, but I think she's a decent looking bike. She's pedal-less because I figured if I was going to be taking the Bianchi out, might as well put the power meter on her for now. Note, in this picture, she only has a 5mm spacer below, and 15mm on top - a configuration I hadn't yet ridden.



For the past few years, her stem/steerer setup looked more like this, with the 10mm spacer above, and the two 5mm spacers below. This is with the 110mm stem I just put on; previously she was with a 100mm FSA stem.




Pulling that stack off, I do see the mark that was the question of the first post. I also see a similar line above. These marks roughly correspond to where the stem clamps the steerer. I will note: I can definitely feel the ridge on the lower mark, but not the top one.




The expander plug next to the steerer, and inside the stem - even without any spacers on top, the stem's bottom bolt would overhang the OEM expander.





So from the looks of it, here's my hypothesis:
1. The mark(s) on the steerer tube are caused by the stem. the upper and lower marks line up to the upper and lower clamping bolts on this stem, which is very similar to my older stem.
2. It's possible that the lower mark is more pronounced due to the lack of internal support on the steerer. As far as I recall, I've always used a torque wrench to tighten the stem, and I don't recall ever going more than a smidge past 5.5nm, and I've done my best to tighten both bolts evenly. I'm still skeptical, but there's also evidence.

I'd love to hear any other thoughts or ideas. Her front end is only lightly reassembled at this point, so pretty easy to take any additional pictures, as well. Thanks!

aliasfox

To be honest, I don't remember where I read it. I basically took it to mean "set the expander plug only as tight as you need it to properly set your headset preload." As I had never believed that little thing was important for resisting the stem's clamping forces, that's how I did things.

SoSmellyAir

What direction does this ridge extend? Around the circumference of the steerer at the bottom of the stem?

The expander plug is way too short.

I think your hypothesis is correct. Using a torque wrench and respecting the specified torque does not obviate the need for an expander plug to counteract the compression by the lower stem bolt. Everything I have read says that hollow CF tubing is susceptible to circumferential compression force. The unsupported segment would just compress, thereby requiring more rotation of the torque wrench before you reach the specified torque. That said, I cannot say whether the ridge indicates that the structural integrity of the steerer is compromised.

Kontact 

It is worthwhile to remember that carbon fiber composites are just reinforced plastic. There is no way you can clamp metal to them and not have some compression marks. But that narrow mark on the back of the steerer is hardly anything compared to how much of a beating a carbon dropout receives:



And every carbon frame with a clamp on front derailleur has a pretty obvious crease by the clamp bolt.

aliasfox

The ridge goes vertically along the length of the steerer. In the picture in the original post, it shows up as a white line. It's visible in the series of pictures in my later post, sticking out just above the headset top cap.

Enve lists Palo Alto Bicycles as a dealer, I'll see if I can bring the bike in today. Maybe I'll be lucky and they can claim warranty or incidental damage and shave a few bucks off of a replacement. I'm pretty sure I'm no longer confident to take this bike on the Gran Fondo I'm attending in April, not with a potentially damaged steerer and -10% descents.

aliasfox

True, but in those examples, I'm pretty sure a dropout isn't actually hollow, and while a seat tube is, I'm going to guess that a failure there is a lot less likely to throw one off the bike, face first - I imagine you'll stomp on the pedals, notice the bottom bracket swaying more, and your front derailleur rub the chain with each pedal stroke. That sounds like a car ride home (or a very gingerly ride, if one isn't too far), whereas a broken steerer sounds like an ambulance ride to the ER. or worse. Given that quite a few cyclists have called out that this doesn't look normal/doesn't look like something they've seen, I'd rather get it checked out.

Definitely want to mitigate the risk of catastrophic failure, even if it means a new fork. It seems that peace of mind is worth a lot to me these days...

eduskator

Well that's a bold statement. Are you saying that compression plugs aren't useful to counteract the stem's clamping force and avoid material failure as a result of a strong force applied to a small portion of the tube?

SoSmellyAir

Now I see. It is the vertical white line (a) extending longitudinally on the surface of the steerer; and (b) coinciding with the gap of the stem at its lower bolt. It does not look that bad; how deep is that ridge?

Is this the dealer who had assembled the bike with a much too short expander plug? Otherwise, I am not sure if it would be covered under warranty. Regardless, I hope Enve extends you a significant goodwill discount toward a replacement fork, with a lecture to use a long expander plug. Good luck.

aliasfox

It’s deep enough to feel it when you run your finger over it, probably less than a millimeter. That said, my view on a failure here is that there really isn’t a degree - start of a failure means a failure, in my book. I don’t want it realize it’s progressed further just as I’m slamming on the brakes going into a hairpin descent.

The bike is a Lynskey, ordered direct from the manufacturer in summer 2019 (I think they’d gone factory direct by that point). However, PA Bikes used a similar expansion plug on the gravel bike I built up when we got out here last summer (had them cut the steerer tube and assemble the front end). I use that almost exclusively as an around-town bike (flat bars and rack mounts), so less of a concern… but I’ll check that bike too. Maybe I should order two of the long expanders before something happens to that fork - wouldn’t want to have to replace the color matched fork if I don’t need to.

I should still have the receipt for the bike purchase, but not sure if that would help much. Lynskey was back ordered on their own forks, so I was given the Enve as a no-cost upgrade for them to get the bike out the door. Not sure it’s actually listed anywhere on the digital receipt. We’ll see after work.

rm -rf

The "vertical white line" --- is it the green scrape marks, or the purple line?
That purple line looks like an edge of the carbon wrap, very normal.



~~~
The scrape marks don't seem to match up with the shape of the stem clamp. Is there a sharp, vertical internal edge on the inside of the stem clamp?

rm -rf

Around 2014, there was a page on BianchiUSA.com, about steerer damage from incorrectly installed stems. It appears to be gone from the internet, but a couple of the images are in this old post I did:
https://www.bikeforums.net/21006763-post22.html

There's a "not damaged" photo, and a "steerer tube damaged" one, and an extremely crushed image, too.

~~~
Steerers are quite strong. Even the short, cutoff end after I shortened my steerer was sturdy.
I wouldn't worry about surface damage, but I'd be concerned about crushing extending farther into the layers, especially if it's been ridden at lot over rough surfaces with an incorrectly tightened stem. I could expect the damage to get worse over time.

Those green arrow scrapes seem to be on the surface?

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.

aliasfox

The green arrows point to the issue in question. In fact, it's the bottom arrow that's most concerning, as there's definitely a ridge that can be felt.

This particular stem is new to the bike, as I decided to go a little more stretched out and aero. More saddle time in CA means more flexibility, and the 100mm stem was starting to feel a little cramped. I'll take a picture of the old stem when I go out to the garage later. Not exactly the same, but still a two bolt clamp with opposed bolts.

The frame and fork have just over 5.1k miles on them (about 1.6k between July and Dec of last year). Definitely getting a lot of use recently.