Buzzkill53120

I recently bought a NOS 2019 Trek Domane. I did my measurements, cut the fork to length, all good. I ordered all the frame bits I needed and a expander plug.

So my original setup I had: 40mm of spacers below the stem and a stem stack of 40mm. With the expander plug in, it added 2mm on the top of the steerer. I had a gap of 3mm from the top of the steerer to the top of the stem, enough to set the headset pre-load.
I came across an article from Trek in 2010 recommending a stack of no more than 40mm between headset and stem and a minimum of a 5mm spacer on top of the stem. So I rearrange the spacers, 35mm between headset and stem, put a 10mm spacer on top, which left me 5mm of gap from the of the expander top.

Now the 5mm drop doesn't hurt my position, so all is good, but I have some questions.
1.) When I ordered all the parts, the expander plug I got was the standard Trek (Bontrager) part. The plug insertion length into steerer is 30mm. Am I correct the expander should be at least as long as the stem stack of 40mm? Are there stems with a 30mm stack? All the stems I have are 40mm.
2.) Can I have the stem flush with the top of the expander flange and add the 5mm on top?

FBinNY 

You're overthinking this.

First of all life isnt binary, and neither are mechanical systems. Guidelines are just that - guidelines - and not black and white absolute lines. They're offered, based on estimates of worst conditions and margins of be error.

So there's more or to less fudge room, depending on how you ride. If you're a large rider who works the bars hard when climbing or sprinting, you might want to be more conservative and not go to the limits. OTOH you might have plenty of safety margin even at maximum stack.

For my part, I'm a big believer in overlapped rather than aligned joints. So IMO, best practice is to have the expander overlap the bottom of the stem. Likewise the streerer should overall and engage the topmost spacer. Beyond that, use your best judgement a to whether it makes sense to set the bike up for maximum comfort, staying close to, even if not exactly within guidelines.

HillRider

I don't know of any expander that tall so finding one long enough to cover the entire 40mm of the stem clamp is going to be difficult, and probably unnecessary. All the expanders I have measure about 20mm long for the expansion portion and all my stems are about 40mm tall so they do not get fully supported and this has never caused a problem in over 200,000 miles of riding carbon steerers.

I've owned and seen two types of expander plugs:
1. Has a flange and sits right on top of the steerer so the depth you can inset it is limited.
2. Can fit down into the steerer as far as you like and be tightened into place limited only by the length of the top cap compression bolt.

If you really want to have the bottom of the plug at or below the bottom of the stem clamp, you will need the second type of expander and a longer than usual top cap compression bolt.

SoSmellyAir

From what I can gather from my model specific manual regarding the vertical positioning of the expander plug assembly within the steerer, the height of the expander plug assembly should slightly exceed the distance between the two stem bolts (that tighten the stem around the steerer).

129387_oms_synapsecarbon_en_low.pdf (cannondale.com). See page 8.

gkamieneski

There certainly are longer compression plugs that will likely make you feel more comfortable. Colnago and Origin8 come to mind. I seem to recall that these were at least 50mm long.

Buzzkill53120

As FBinNY said; "You're overthinking this". He's correct. Doing further reading the expander plug does not need to reach the bottom of stem and the plug I have meets the requirements. I'm leaving it as it is.
This my first experience with a carbon steerer and kind of went down the rabbit hole with it. As with anything on the internet, there are multiple and conflicting theories that can be found. I use BF as a sanity check (some may disagree). So thanks to all for commenting.

Camilo

Just do a search for a long bike expander plug and go from there. There's a lot of options at 40mm. I think I've even seen them close to 2"/50mm long.

oldbobcat

Last time I looked, longer expansion plugs didn't exist, and we assumed that as long as you followed the manufacturers directions, a carbon steerer would be just as strong as a steel or aluminum one. But I had to investigate, and I found that some manufacturers require steerer reinforcement from the expander, and some manufacturers make steerers with so much gapping in the layup and porosity in the resin that I wouldn't ride them under any circumstances. Learn something every day.

FBinNY 

You hint at my single biggest problem with CF frames.

In metal frames the key elements of structural integrity are set by the tube mills, and demands on the builder are limited. Sure there's room for builders to screw up, but not doing so is fairly easy.

OTOH in CF structural integrity is controlled at assembly, as the sheets are laid up, leaving plenty of room for serious consequences from poor work

Given the anonymous outsourcing of these frames and forks, I have a tough time taking them on faith alone.

oldbobcat

Back in the previous century I rode steel frames. The thought of a frame warranty never came up because you could look at a bike and determine the quality. Sure, there were surprises, like Peogeot UO-8s made from seamed tubes, in defiance of the label on the frame, and counterfeit Gioses, but if you bought from a reputable dealer you were covered.

In the oughties I bought a lightly used Giant TCR that practically disintegrated under me. By the end of my third season on it, it would visibly sag when I sat on it. You can imagine how it handled downhills in a crosswind.

I replaced it with a Trek Madone, mainly for its lifetime frame warranty. Ten years later, I haven't had to use it.

Camilo

But they do. as long as 40 - 50mm. A simple search finds them. Deda Elementi is one source among many more generic brands.

oldbobcat

That point was perfectly obvious from this entire discussion.

Camilo

Sorry. i must have misunderstood what you were saying
I apologize if I'm not getting it.

maddog34

a quick search on Ebay and a bit of scrolling brings up... 68.5mm length expander for Carbon Steerer... from Deda Elementi... :-D

Manufacturer Part # HDEXL23X70

thereare some others that look to be about 40-50mm long too... i saw 22, 23, and 23.5mm listed for OD on the expander.. for differing thickness tube walls, i'd recon..

nomadmax 

I have but one bike that has a carbon fork/steerer. I use an expander plug that's 90mm in length, it extends thru the steerer tube, past the stem and into the headtube (where the steerer is supported by the bearings). That said, I only run 20mm of spacer under the stem.

base2 

So what you're saying is you have a fancy carbon fork with a fancy carbon solid aluminum steer tube...

oldbobcat

Apology accepted.

For everybody's edification, here's what I found on carbon steerer failure, from Luescher Teknik: Some of this is from user error, like overtightening stem clamps. Some is caused by seemingly trivial stem defects. Some is from manufacturing defects of the forks.

And here's Luescher's beta on compression plugs. There are some pretty lame products out there, eh, Cannondale? It doesn't take too much to deform a unidirectional carbon steerer with a compression plug.

And in case you thought bonded forks (carbon blades with alloy crowns and steerers) were immune:
As I previously stated, this is new to me. When I started working on carbon bikes, in 2008, manufacturers implied that as long as you followed their directions, a carbon steerer would be just as strong as an alloy one. So, theoretically, after setting the compression plug, aligning the stem, setting the headset preload with the stem cap, and torquing the stem clamp bolts to spec, your could remove the top cap and compression plug and still ride the bike. I'm sure some weight-weenies have even tried this. Now we know that due to design concessions to weight reduction and manufacturing defects in the fork and stem, this would be foolhardy. Indeed, one or more of these factors likely led to George Hincapie's famous crash in the 2006 Paris-Roubaix, caused by a fork failure that Trek never satisfactorily explained.

I'm grateful that this thread directed me to these podcasts. It's shocking that after education with Park Tool, Shimano, SRAM, Trek, and Specialized, I've only come across them since this week. I'm sure many riders and mechanics will only come across them after something breaks. I wish more riders could see these before doing stupid things with carbon forks, like using non-carbon-rated stems, uncut steerers on small frames, and bolt-on steerer extenders. The neck you save might be your own.

gkamieneski

If I were the OP I would pay attention to the changing trend to this conversation. I mentioned examples of very suitable 50mm plugs way back in message #5. Most common stems now have 40mm between clamping areas.

jds108

80mm expander. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If one believes that the expander adds strength/support to the steerer, the perhaps the expander should cover both the area inside the stem as well as the top of the headset. Remember the latter is where Hincapie's fork broke.

oldbobcat

I just found this. www.cyclingnews.com presents the 104th Paris-Roubaix
Hincapie was using a custom fork with an aluminum steerer. His stem was practically slammed. Here's a photo of the failed section. It looks like it broke right above the wedge washer


So it looks like Hincapie's fork is a red herring in this discussion. I'm sorry if I've misled anybody.

oldbobcat

In the same search, I found this example from "local strongman racer." He said he "pulled a Hincapie."

It looks like he had at least two spacers below the stem and this break occurred at or just below the top one. His stem is clamped at the very top of the steerer, in the "crush zone," and there's no evidence of a top cap or expansion plug.

SoSmellyAir

Even after the steerer snapped, the expander plug may still (precariously) connect the two now separated part of the steerer. So perhaps the strongman had to remove the top cap and expander plug to take this photo?

oldbobcat

I see it now. The bar is flipped upside down, the steerer broke right at the stem, and it's an alloy steerer because there are no stray fibers at the break. Should've used carbon.