johngwheeler

I asked my bike shop if I could try removing one of the 10mm headset spacers on my Merida Scultura, and they suggested putting a round spacer on top of the stem like this (at least temporarily):



stem with 10mm round spacer and top cap


I have read that some manufacturers advise against this because there is a possibility that clamping the stem lower down the carbon steerer tube may not be supported by the expansion plug that sits inside the top of the hollow steerer tube, so that the stem clamps on "empty steerer", which could deform or crack. The pictures below show the steerer tube and expansion plug without the top spacer and top cap:


Steerer tube with expansion plug from top

Steerer tube with expansion plug from side

I don't know how long the expansion plug is, and didn't want to mess around with it without knowing what I am doing. The bike shop didn't really understand my concern and they didn't offer to remove the plug to show me how far it goes into the steerer tube, so I have no idea if the stem is clamping onto an unsupported section of steerer tube or not, and if this is OK temporarily or not (i.e. until I decide on whether the lower stem height is correct, and have the steerer tube cut down by 10mm.

Are any of you familiar with this particular stem and expansion plug and can advise?

Many thanks!

Iride01 

What do you feel is wrong with doing that. It's a common thing to do for any threadless headset where you don't want to cut the steerer tube. It allows you to change up your bar height in two directions instead of just going lower.

Your expansion plug shouldn't change from it's location with the spacer underneath the bar. So if you are just going to put the spacer on top or another spacer of equal thickness to what you took out, don't mess with the expansion plug.

There might be some concerns for very proprietary stems and integrated bars/stem combo's. The only concern for yours is likely just aesthetics.

Arrowana

Most likely you are fine, but you won't really know for sure unless the compression plug is pulled out to see how long it is. If it is long enough to support the steerer tube where the stem is clamping it in it's new position, you are fine. If not, you may want to get a compression plug with more length, Whisky Parts makes one that should do the trick. Either way, if you remove the compression plug, make sure it is re-installed with a torque wrench. You don't want to risk damaging a steerer tube.

Andrew R Stewart 

Not mentioned is the steerer material. The shine on the exposed steerer in the second image suggests an Al steerer. Is this so?

Al steerers don't really need an expansion or pressure plug and pretty much where ever you locate the stem (and thus apply clamping pressure) should be fine. However carbon steerers do need the added reinforcement.

Interesting that some carbon fork instructions require a short height spacer above the stem and below the top cap. This is to ensure that the stem clamp is not too close to the top and open end of the steerer. Too close to the top or if the stem extends above the steerer (as is OK with an Al steerer) can concentrate the compressive forces the stem's clamp produces too close to the unsupported and open end of the steerer and lead to a crack.

I would defiantly follow the fork brand's instructions on this detail. If you are the type to later complain about a steerer cracking from a poorly located stem (and/or poorly supported steerer top end) then have a shop do this and have them write up a service ticket for future reference. Of course this added assurance should cost something: Andy

johngwheeler

My concern (from reading various posts on this subject relating to carbon steerer tubes) is that if the steerer tube is not cut and the stem is moved to lower down on the steerer tube, it will eventually be clamping onto "empty tube" that is below the expander plug. e.g if the stem is 5cm high and so is the expander plug, then moving the stem 1cm lower down the steerer would mean than the bottom 1cm of the stem is clamped on to a hollow section steerer tube that is not filled with the expander plug. This is presumably weaker or at least more prone to compression forces that the top part of the steerer that is filled with the expander plug.

Whether this is a problem or not depends on (a) the length of the expander plug - it may be longer than the thickness of the stem which gives some latitude, and (b) whether having the stem clamped onto "unsupported" carbon steerer tube is really a bad thing.

johngwheeler

Thanks - this sounds like the best approach, but I don't currently have a torque wrench (I'm travelling for several months, hence the interest in whether this is safe for a couple of months). I might try a different bike shop which understands my concerns better!

[Edit: I found some photos in the Merida instructions regarding the fork setup. It's not the same fork and stem as my bike, but it does show a quite long expander plug, which if fitted in my bike, would certainly be long enough to cover the entire stem height plus the 10mm spacer placed on top. But as you say, the best option is to remove the expander and check it, and then replace it, with the correct torque - although I would get a bike shop to do this for me given my lack of tools and experience. I have read some horror stories of steerers getting cracked even within the manufacturer's maximum torque limit. ]

johngwheeler

I think I mentioned that this concerns carbon fiber steerer tubes, which applies on my Merida bike. The manufacturer warns against riding "long term" with "several spacers" above the stem, but does not put any exact numbers on this, or gives details of the length of the expander plug.

There is no "open end" of the steerer tube on my bike - as you can see in the photos, the steerer has a plug in the end with printed details of the required position and torque.

With all of the spacers (25mm) as delivered, the top of the carbon steerer tube (which is filled with an expander plug) is actually slightly below the top of the stem, but probably just above the point where the top stem clamping bolts are, so I presume this is OK. There is only the top-cap that sits flush with the top of the stem, and 2-3mm above the top of the steerer tube (the top cap screws goes into the thread in the centre of the expander plug, but presumably has no "structural influence" once the stem bolts are tightened).

Andrew R Stewart 

But that's Ok with me, it's your face. Perhaps others will be able to explain in a way that you will understand better. Andy

Iride01 

Take your expander plug out and see for yourself how long it is. Different brands and models are different. If this bike is as was originally new, then I'd expect that they put a plug in it that is long enough for you to remove spacers and put them on top or substitute similar width spacers if the profile of the lower spacers just looks too odd on top.

Or, you can cut the tube to what ever the proper length is. Just make sure you are certain where to cut. But when you do so, you won't ever be able to go higher if you later decide you don't like being that low.

You can find all sorts of contradictory information on the internet. Many times that's because different manufacturer's designs are different enough to require different ways to do things. So if you aren't looking at the instructions and manufacturer recommendations for that bike and it's fork/steerer tube if different manufacturer, then it's a toss up if you are finding information that applies specifically for your stuff.

Kontact

Hey Andy. I read both of your posts, and I'm not really sure what you are warning against.


In general on this topic, there are stems which can only be used with a flush cut steerer (no spacers above, like Enve Aero), and there are steerers that the maker says must have spacers above (Trek). Since Enve is a carbon fork maker, I would presume that they know that at least some carbon forks are fine with no spacers. Since Trek says you have to have a spacer on their bikes, they have their own limits that would prevent someone from installing that Enve stem. The expander plugs with a 1 1/8" diameter lip seems very safe since the stem is actually clamping the plug, which acts as a limiter.

Lacking any specific guidance for a fork, it ought to be able to be used either way.

If Merida wants a certain set up, that's probably worth doing. But it seems like their concern could be addressed by getting a very long compression plug so the plug overlaps the stem the same way the factory one does with a shorter steerer.

johngwheeler If you don't know what expander plug you have, don't assume. Merida is the largest bike maker on earth, so that photo you found does not tell you anything about your bike in specific.

And if you don't have a torque wrench and are concerned about your steerer, how are you moving your stem around?

johngwheeler

Thanks for your reply - I totally agree with you that safety is paramount, hence my reason for posting this question in the first place! Perhaps my language wasn't clear enough when I described how the bike was set up from new (BTW, it's a 2023 Merida Scultura 6000).

What I meant by saying "there is no open end on my steerer tube" was that the top end of the steerer tube has (what I presume is) an expander plug fitted in to it, so it no longer open (i.e. a hollow tube). This is what (I think) I am showing in the photo below:


steerer tube with expander plug - above stem after removing 10mm spacer

This photo was taken after one of the factory-fitted 10mm spacers was removed from below the stem, the stem lowered, and the headset adjusted with the lower stem position. While the hex bolt of the plug is below the top of the stem, the top of the expander plug (and by extension the top of the steerer tube is now well above the top of the stem (by about 6-7mm). This could be interpreted as being inherently "safer" because the stem is not clamping on the extreme end of the steerer tube. However, in the factory-default configuration, before the 10mm spacer was removed and the stem lowered, the top of the steerer tube (with its plug) was actually about 3mm *below* the top of the stem, although still just about above the level of the top 2 stem clamping bolts. When I said that "I presume this is OK", I meant that if Merida ships the bike in this configuration (steerer tube below the top of the stem), then I have assumed that this is a correct and safe configuration in the absence of any contrary information.

My doubt is that I don't know how essential it is to have an expander plug that is at least as long as the height of the stem - to ensure the stem always clamps onto a "supported tube", or how long the actual plug used by Merida is. The obvious answer is to remove it, measure it and replace it, but I would need to get a torque wrench to ensure correct tension, and I have never experimented with these components of a bike before, so I'm hesitant to do this without fully understanding how everything works. I'll probably just find a bike shop that understands what I'm trying to determine - the one that removed the spacer and fitted a temporary round spacer above the stem didn't think this was a problem, but I would like a "second opinion". Bike mechanics (like doctors) are not infallible :-)

johngwheeler

Thanks. The instructions that I have seen on the Merida web site look pretty out of date and looks nothing like the FSA SMR stem fitted on my 2023 bike (https://d2lljesbicak00.cloudfront.ne...fork-en.pdf?p3)

I am hesitant to cut the steerer tube, particularly to only remove a 10mm "chimney", until I am really sure that the position is right for me "long term" for long rides and accounting for possible loss of flexibility with age.

The purpose of my question is to see if there is anyone who is actually familiar with my particular bike (2023 Merida Scultura 6000) without me having to go into a bike shop and explain everything (in a foreign language, because I'm travelling at the moment).

The bottom line is this: If the stem *must only* clamp onto a "supported" section of the carbon steerer tube (i.e. a section filled with an expander plug), *and* the fitted expander is longer than the thickness of the stem plus 10mm, then I should be fine.

The best option of course is to actually remove the expander plug to determine this, and try to find some more definitive information from Merida; what I have a rather vague and indefinite.

johngwheeler

Thanks for your reply, and for the advice not to assume what kind of expander plug is fitted in my individual bike. Looking at Merida's documentation, there list the same part number for the expander plug on multiple versions of the Scultura carbon frame: see https://d2lljesbicak00.cloudfront.ne...ra-cf-v.pdf?p3 . They all show: Part #24 A2054000107 EXPANDER for fork steerer ID 23.6mm, 6-8Nm torque

The line diagram in the document *looks* like the expander is "quite long" - enough for the stem and at least 1 or 2 spacers, but of course this is hardly an engineering specification! I will try to get an answer from Merida.....

In answer to your question, I went to a smaller subsidiary bike shop to the one I bought the bike from, and they removed the spacer for me during an initial 4 week service they offer on new bikes. I didn't see how they did it, or if they did anything with the expander plug (I doubt it). They didn't see any problem leaving a 10mm spacer on top of the stem, but I have my doubts about whether this small shop does a lot of work on carbon road bikes based on seeing them adjust my bike (saddle, seat post, bars etc) without using a torque wrench once. They may just be so experienced that they don't need a torque wrench...but it left me with doubts about the advice they gave me, hence my post.

johngwheeler

Just to add a bit of extra information, I found a more detailed installation manual for the top-end Merida Scultura Team SL model. This has an integrated cockpit, but notably uses the same expander part as my bike model. From https://d2lljesbicak00.cloudfront.ne...0220812.pdf?p3


Merida Scultura Team SL cockpit setup


This would appear to indicate that there isn't an inherent problem having spacer above the stem, but the same document also mentions than in addition to the expander plug inside the steerer tube, there is *also* an alloy sleeve that surround the outside of the steerer tube, which is shown as at least as long a the entire combination of headset, spacers and stem. I don't have this cockpit (no extra alloy shim/sleeve) so I can't use this as a definitive guide that my current setup is OK, but it provides some interesting information nevertheless.

Andrew R Stewart 

johngwheeler- Sorry if my posts sounded a bit flamey or condescending. I had a poor first part of the day yesterday and it showed in my reply. But I think my points are still valid.

Different fork makers have slightly different limits on stem placement and spacer use. I strongly suggest following these and said as much. I haven't yet seen top end (the "open" end) carbon damage that was enough to cause an "incident", while riding. I have seen a few carbon tubes damaged from compressive forces when the clamping wasn't where the manufacturer wanted it to be. Here's a shot of a carbon post I replaced just last week for a friend. The post does have an Al insert inside about at its mid length and there is an indicated section where the company wanted the post to be clamped. The insert didn't extend far enough up inside the carbon shaft and the rider has short legs so the post was clamped just above where the insert is. You can see the crack on the OD and inside too. My friend never noticed this and when I told her of it she did mention that the seat had been easy to rotate WRT the frame, no doubt because of the now smaller diameter at the cracked point.

The risk I mention is if this were to happen to one's handlebars, their not staying put, when riding and as is often the case this unexpected stuff happens when the stress is the greatest. Like when doing some unexpected avoidance maneuver. And this is the lesser of the dangers. The greater one is if the steerer does crack and is not noticed till the crack has expanded/grown to the point where the stem's ability to stay attached to the rest of the fork becomes "questionable" (and just breaks off?). That any cracking is covered/hidden by the spacers and stem make this monitoring far less likely to be done on a periodic schedule, if at all.

I have seen the results of handle bars and stems breaking apart and the rider's injuries. I would expect a broken off top of steerer would have similar possibilities of harm too.

The shops I have worked at (during the carbon steerer craze) all followed the "add a small spacer above the stem to insure that the stem is not stressing the top end of the steerer" i8nstructions that brands have provided their dealers. For fitting purposes we will leave a bit of steerer uncut with above the stem spacers as needed to adjust the headset preload. On the follow up fitting session we might complete the steerer's cutting down, or not. Andy

johngwheeler

Thanks Andy. Manufacturers seem to be one of two camps with regard to spacers over the stem: either have a small (2-3mm) gap from the stop of the stem and the top of the steerer tube (with an expander plug) *below* the top of the stem, or have the steerer tube go completely through the stem, with the top 2-3mm *above* the stem, and then put a thin (5mm) spacer on top of the stem so that the top-cap doesn't touch the steerer.

The latter option instinctively sounds "more secure" because the stem is not clamped right at the extreme end of the steerer tube. However, Merida, and no doubt other manufacturers, choose the first option. I expect this is safe enough because (a) the steerer has an expansion plug that is mitigating the clamping force of the stem on the steerer tube so clamping forces at the end of the tube should be well tolerated, and (b) the top of the steerer tube (with its plug) is still just above the top stem clamp bolts so the stem isn't clamping "into thin air" at the top and onto the steerer tube on the bottom.

For reference, my stem is 32mm high and the top & bottom clamp bolts have 20mm between them. There is 8mm from the top of the stem to the centre of the top stem bolts, so even if the top of the steerer tube were say 5mm below the top of the stem, the top screws would still be applying pressure on the top of the steerer tube....although the force is clearly not only applied where the stem bolt sits, but through the whole interior surface of the stem.

I have seen some photos of failed carbon steerer tubes and it definitely looks like something best avoided!

Many (most?) manufacturers state that if more than "a few mm" of spacers are to be placed above the stem, that the expander plug must be long enough reach the bottom of the stem, which is of course where I have some doubt. It makes instinctive sense to me that the stem should clamp onto the "reinforced" length of the steerer tube, and have equal torque on all bolts. Having half the stem attached to a hollow tube would create unequal forces and would be asking for trouble....

I'll just have to determine the actual length of the expander plug to find out what's really going on inside the steerer tube. My calculation is that the expander plug needs to be at least 38mm long to cover the entire stem height (32mm) plus 6mm for the part of the steerer tube above the stem.

Legenders

Hello Johngwheeler,
have you found out something about the Expander? I wanted to remove mine, but i couldnt pull it out. I removed the part which you put on top (the one which has "FRONT" written on it), and then i put in a Screw and tried to pull. Unluckily it didnt move any bit. Now a friend told me that i should hit it downwards a bit, but i havent tried yet.

Camilo

I just use expansion plugs that extend into the steer tube enough to back up both stem clamp bolts. Then I don't worry about how many spacers are above the stem, aesthetics aside. Plus, I'm careful about torquing the stem bolts

SoSmellyAir

To remove the expander plug from the steerer, one must first loosen both the expander plug (i.e., by turning the silver hex part shown in post 11 above) and the stem bolts.