Kontact 

You'd gain all 5mm, since the steerer is normally not cut level with the stem.

5mm matters to some people. So do aesthetics. Your values are not everyone's values.

But you asked the question "why?" and got 7 reasonable answers.

Bah Humbug

This is a very odd windmill to tilt at.

Kontact 

Obviously not. We're talking about being able to get rid of a mandated top spacer and move the stem up an additional 5mm on a previously cut fork.


The emoji can be used for anything in cycling. And it's not really of any value:

Aheadsets.

Carbon forks.

Road bikes.

Your opinions vs my opinions.

DaveSSS 

I don't want a bulging steering tube or a slipping compression plug. I also have bikes with modern one piece aero bar/stems that look kind of stupid with anything but a flush top cap.

Even epoxy is not totally permanent. Star nuts can be drilled out, but they're steel and I can't imagine damaging the threads. The thread inserts made for wood can easily be drilled out.


​​​​https://www.mcmaster.com/products/in...hread-size~m6/

Lombard

Obviously not what? Being able to raise the stem higher than the fork specs? I'm not interested in cutting my fork, I'm interested in safely getting as upright as possible.

Sarcasm emojis were for the minuscule weight savings. Maybe you mentioned that tongue in cheek
......or not, I don't know.

Kontact 

It was also for the "everyone looking at my extra spacer".

Reinforcing the steerer tube at the level of stem clamp isn't going to reinforce it down at the headset against the increased leverage of more exposed steerer between the headset and stem. Leverage is the reason for the spacer stack maximum. Sorry that I assumed that was obvious.

You could certainly reinforce the steerer to extend the minimum spacer stack higher. I would do that by getting a piece of carbon or fiberglass tubing with an outer diameter just a bit smaller than the steerer's inner diameter and epoxy it down into the steerer, well past the upper race - if not all the way to the crown. This would make the steerer rigidity closer to that of a steel steerer, where we normally don't worry about spacer stack.

Lombard

Well yeah, I thought that was funny too. But if your primary objective is to eliminate that "unsightly" top spacer, the only way to do that is to cut the steerer.

And that was my assumption as well. So then I really don't understand what your previous idea of epoxying unless you were talking about doing the following:

tomato coupe

Whether it's 3mm or 5mm doesn't really matter. You're still describing a scenario where someone that is very picky about stack height buys a used bike with a steerer tube that's been cut too low to achieve their desired stack height when using a compression plug. An epoxy plug might be a great way to fix that problem, but it's an uncommon scenario. It doesn't address the vast majority of cases, which involve new bikes or used bikes where the steerer hasn't been pre-cut precisely 5 mm too low.

Yes, and that's what I stated: I think there's been only 2 -- aesthetic value and your special case of the pre-cut steerer, and the latter doesn't address the general case.

Kontact 

The epoxy plug replaces an expander and is much less likely to slip, provides and un-crushable steerer tube/stem interface and makes the top of the steerer less likely to split when used flush with the stem.

Kontact 

You're forgetting that people who already own bikes sometimes need to change their fit. As a fitter, I would say sometimes 5mm is enough.

Why is it you think that having a stronger stem clamping connection with a lighter plug that can't creep isn't useful?

No one is suggesting anyone should do this, but this denial that it has any value is a bit silly. Several bike companies make their steerers in a similar manner - like BMC and Cervelo.

tomato coupe

Nope, haven't forgotten that at all. As already mentioned, filling your steerer with epoxy doesn't lend itself to future changes as well as a compression plug does.

Kontact 

Aren't the you one saying that raising your stem 5mm is unimportant? Now you want to be flexible?

If you want to cut 4cm off the steerer, you'll be past the plug. If you want to cut 2cm off the steerer, you'll still have useful threads and a plug that is no less strong than an expander. So I don't know if there really is a problem.

tomato coupe

Filling your steerer with epoxy limits future changes more than using a compression plug. Whether or not a 5 mm change is significant for most people is a completely different issue.

Unless you fill the steerer tube to its full depth and also thread the plug to its full depth, you will be limited in where you can cut the steerer tube and still be able to re-use it. And, if you do fill the steerer tube to its full depth, you certainly will give up any chance of saving weight.

Kontact 

Well, no. If you have an inch of thread from the modified starnut, that will allow you to cut it down pretty far.

And if you cut it down to about 1cm, you can knock out the plug with a rap from a mallet. The epoxy makes a good bond, but it isn't not as good as the bond holding the steerer carbon together. Then you can do whatever after that.

So I don't see the problem. The "worst" thing that could happen is that you think the shortened plug will hold and it doesn't. Then you replace it.

Like I said, bike companies do this all the time and its been figured out. I have cut down many Cervelos and BMCs with "permanent" plugs.

rsbob 

Jumping on this thread with something related. Have a 2020 Bianchi Infinito carbon that tends to develop a wobble in excess of 30 MPH. Have two different wheel sets and has happened with both. Was passing by a bike shop that sells high end bikes in Seattle for their opinion. I have 5 spacers on the stem, so their thought was to remove one. While the were removing the spacer, the tech really tightened down the steering tube plug to the point the wheel no longer swings freely when I pick up the bike. It doesn’t take force to move it, but it is really snug. On a carbon bike, is there such a thing as a too tight plug which might compromise the head tube? Did a couple of descents today but not over 38 and it felt super stable. Loosen it just a bit?

Lombard

If the wheel doesn't turn freely, it sounds like he tightened the preload too much, not the plug itself.

Kontact 

Some plugs have two separate bits of hardware - a bolt to tighten for the expander, and a top cap bolt that solely controls bearing preload. Some plugs just have a single screw that simultaneously tightens both (those usually suck).

So which kind do you have, and which screw are we talking about tightening?

If we are talking bearing preload, most aheadset headsets have seals and need to be tightened to a point where they do not allow the headset to swing completely free. With the bike dangling from the stand to make the headtube vertical, a slightly loose headset will allow the front wheel swing back and forth several times if you start with it turned. When correctly set, it will swing past centered maybe once before returning to center and stopping.

If your seals aren't dragging the headset a little bit, they are disguising a loose headset. It sounds like the mechanic either got it right or it is slightly too tight. It makes sense that your shimmy went away if your headset used to be slightly loose.

If it is too tight, just loosening the top cap isn't going to do anything. Gotta loosen the stem bolts, make your adjustment, then re-torque the stem.

rsbob 

He removed the top cap which holds the spacers and tightened a bolt inside (the expander?). Wonder where to find the proper torque value? Will have to remove the cap and see if there is a value printed on, or next to, the bolt.

Kontact 

There is no torque value for the expander.

The headset preload comes from the other bolt through the top cap. He adjusted both.

SoSmellyAir

If we are talking about this type of steerer expander plug ...

... then there is usually a torque value for the expander, right? See, for example:

Carbon Steerer Tube Plug | Specialized.com

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

Kontact 

Many don't, and the torque doesn't have a real direct connection to how well the plug bites into the steerer. Use no more than necessary.

Lombard

If there is no torque spec, how do you know how much torque is enough so the plug doesn't creep buy not too much that you damage the steerer?

Kontact 

If it moves when you tighten the top cap, that's too little

Lombard

Ha! Obviosly you need to get it tighter than that.

SoSmellyAir

Well, all three in my possession do; the two above plus the one in my Stigmata.