Proper Use of Expander/Compression Plugs

[backdoor]

I recently chopped the steerer tube of my 2 carbon framed bikes to get the front end dialed in.

Before this I had never chopped a carbon steerer before and some recent threads had encouraged me to do a little bit of research on cutting the steerer and the proper use of expander/compression plugs in a carbon steerer.  I couldn't find a whole lot of detail online (even parks website is vague) so I have compiled what I was able to find through conversations with other bike mechanics and online information.  I started this thread to give back a little of what I have picked up along the way and let you guys (and girls) do what you want with the information.  Feel free to add, change or update any information as you see fit.

The 2 bikes I have for reference are a 2013 Ridley Helium and a 2017 Blue Competition Prosecco.  These both have standard threadless Carbon steer tubes with 2 piece stem and handlebars.  Here is the collection of expander plugs I have had to work with  - 



The Ridley expander plug is a 6cm dual sleeved plug.  It has 2 very thin alloy sleeves, one slides into the other to evenly distribute the force of the compression plug against the steerer tube.


The plug that came on my Blue Competition is a common style plug used in many carbon bikes these days.  Typically shorter than the stem clamps.  From what I have read, this type of compression fitting doesn't allow for spacers above the stem as it raises the compression plug above the bottom stem clamp. It is designed to specifically protect the top of the steerer tube from being crushed by the stem clamp


The Deda plug is one that I bought to replace the plug on my Blue Competition bike.  It is 4.5 cm long.  It is similar to the Ridley exapnder except that it has a single sleeve that is thicker than the 2 sleeves used on the Ridley expander.


There are (3) main purposes for the expander plug (aka compression plug, headset plug, headset compressor plug). 


1. The first function of the expander tube is to be able to pre-load the headset before clamping on the stem.

By placing the expander plug in the steerer tube and leaving a 2-4mm gap between the top of the expander plug/steer tube and the top of the stem (or small spacer) it allows the pressure of the stem cap pushing down on the stem (or small spacer) to pull up the fork/steer tube tightening the headset from the bottom of the fork steer tube and pushing down on the stem to tighten the headset from the top. (see diagram) 



2. The second is to reinforce the contact area on the steer tube that the stem clamps around.

One of the two mechanics I spoke to said that stem replacement is easy for any cyclist yet most don't use a torque wrench of any kind nor do they understand the expander plug.  The expander plug reinforces the area the stem clamps to and prevents damage to the layers of the carbon fiber (Fiber layers can also loosen over time especially with repeated tightening and loosening of the stem clamp).   The other thing that was mentioned was the collapse of the top of the steerer tube either from too many spacers on top (Raising the expander plug higher than the stem clamp) or over tightening or wear of the tube from the bottom stem clamp that has no expander reinforcing it.

This image shows how spacers on top of the stem could negate the effectiveness of the expander plug



3. The last is to reinforce the steerer tube against the pressure of the riders weight up and down on the handlebars and stem 


I asked a local bike mechanic about this.  He explained it in this way - Take a paper towel tube, think of it as a steerer tube, hold it 1/2 way up and then take your other hand and put some pressure on the very top of the tube and take a look at where the paper tube starts to give way.  Take 2 more paper towel tubes except this time insert one inside the other.  Then do the same thing as above and you will see that the paper tube for the most part holds up for a little longer than the single tube by itself.  The expander plug serves the same functionality. It takes the pressure applied to the steerer tube from the stem clamp and helps to evenly distribute that pressure across the inside of the steer tube.  While the carbon tube itself is probably strong enough to hold up to most forces placed upon it, the expander tube increases the strength of that tube over the life of the bike.  It's repetitive forces over time that wear away at the steerer tube. (He said picture a 250lb guy on a 17lb bike bunny hopping off a 8" curb with a 13" stem and landing with most of his weight on the handlebars)  

Here is an image showing the short expander plug that came with the Blue


And here is an image showing the Deda plug replacing it for better reinforcement of the steered tube



The most common types of damage to the steer tube come from incorrect torque specs on the stem pinch bolts.  Suprisingly just as often from being not tight enough. The movement from the stem not being tight cuts into the steer tube. The other common type of damage comes from a seized up headset bearing that is not turning with the steer tube and cuts into it.

All that being said along with the number of recent posts on steer tube failures, take the time to check your steer tube, stem clamps and handlebars and make sure your expander plug is doing its job.



Sent from my SM-N950U using Tapatalk

[DartanianX]

Great post.

I agree 100% with everything. This is an area where I’m happy to have “functional weight”.

Guys like Durian Rider rolling around with no expander in whatsoever blow my mind.


Sent from my iPhone using Tapatalk

[AnkitS]

Guys like Durian Rider rolling around with no expander in whatsoever blow my mind.

He doesn't do that anymore, in fact, he often talks about proper expander safety.

[KarlC]

[Nefarious86]

The less thats said about that click bait dead shit troll the better....

Sent from my SM-G977B using Tapatalk

[NickJHP]

Last couple of bikes I've put together I've used the Zinn steerer tube inserts, which are epoxied into the steerer tube and replace the compression plug. They also reinforce the steerer down to below the top headset bearing, and when I put one on the scales it weighed less than the compression plug that came with the fork (can't remember the exact weights). Looks like they're out of stock of them at the moment, though.

https://www.bigandtallbike.com/Steer-Tu ... p_380.html

[Bogan]

The less thats said about that click bait dead shit troll the better....

Sent from my SM-G977B using Tapatalk

Tut tut, how could you possibly say that about the beloved smellyfruitrider. And a moderator too.

[Lelandjt]

Here's a thought: At one end your stem clamps a carbon tube that is your handlebar. At the other it clamps a carbon tube that's your steerer. The steerer has thicker walls than the handlebar. Everyone gets very concerned about reinforcing the inside of the steerer with a plug but not the handlebar....

I have no expander in my steerer, or my handlebar, or my seatpost.

[joejack951]

Here's a thought: At one end your stem clamps a carbon tube that is your handlebar. At the other it clamps a carbon tube that's your steerer. The steerer has thicker walls than the handlebar. Everyone gets very concerned about reinforcing the inside of the steerer with a plug but not the handlebar....

I have no expander in my steerer, or my handlebar, or my seatpost.

The handlebar and seatpost are clamped around a continuous tube portion of the bar/post. The steerer tube, if not using a spacer above the stem, is not.

I was not aware of the long Zinn inserts and made my own for my Hong Fu build, not that they would have fit my disc fork anyway (23.5mm ID vs. 23.8mm for the Zinn insert). I used Loctite 648 to bond it in place. Working great with the steerer cut flush with the top of the stem.

[Miller]

Agree, great post. If this forum had a like function I'd use it.

[nickf]

Extralite UltraStar 3 ftw.

I'm in the improper tightening and previous accident/impacts is causing failures.

[musiclover]

I have retired from this forum, not wasting any more time here.

[joejack951]

I have just been thinking about the same thing today, and one thing bothers me here: how can you find the right position of your stem by moving it up and down the steerer (moving spacers up and down around the stem) and have that reinforcement from the plug at the same time? Would you need to cut your steerer to have that support from the plug every time you select and try a new position for a bike fit? Are you not allowed to have all spacers on top of the stem and stem slammed all the way down on the headset?

My take (expanding on what I already posted): The issue of reinforcement with the steerer tube is due to clamping near the end of the tube. It is at that area only where the tube is susceptible to cracking. So as far as your scenario of fitting a bike by leaving the steerer uncut, the tube is not at risk in that situation, at least no more so than your handlebars or seatpost are.

Where I have encountered issues with traditional minimal expanders is getting enough headset bearing preload, a situation that is exacerbated when the stem is not supporting the OD of the steerer tube. The steerer tube deforms fairly significantly (0.1-0.2mm) as the expander is tightened and sometimes it still slips, especially with the higher preload requirements of cartridge bearing headsets and disc brakes.

Coupled with my dislike of the spacer-on-top-of-stem look I went and made my own solution.

[backdoor]

I have just been thinking about the same thing today, and one thing bothers me here: how can you find the right position of your stem by moving it up and down the steerer (moving spacers up and down around the stem) and have that reinforcement from the plug at the same time? Would you need to cut your steerer to have that support from the plug every time you select and try a new position for a bike fit? Are you not allowed to have all spacers on top of the stem and stem slammed all the way down on the headset?

As mentioned above, the use of the expander plug directly reinforces the top of the carbon steerer from collapsing as well as reinforcing the shape of the steerer tube from the compressing force of the stem.

That being said, I rode both my bikes for an entire season before deciding where to trim the steerer tube. No damage was done to the steerer during that time (I was overly cautious of over tightening the stem an did use a 6cm expander) Just be careful that you don't put enough pressure to change the shape of the steer tube.

Damage to the steerer tube can happen over time with the weight of the rider constantly putting pressure on then off then on the handlebars. The pressures put on the steer tube are omni-directional and will damage the steer tube over time.

And another subject related to that: a youtube blogger from the Rides of Japan channel talks about saving some weight on the plug and using a really minimalistic short cheap plug from aliexpress and says that it has very minimal functional value...

PS My personal opinion on the matter that the role of the plugs in exagerated but they could be useful in case of a crash. However, it is just the matter of the strength and spot of the impact and luck in the end.

Someone mentioned above about a glued in compression plug which is much lighter in weight and does the same job. You just have to make sure your steer tube is cut where you want it before gluing in the plug as it looks like a permanent fixture once the glue dries.



Sent from my SM-N950U using Tapatalk

[andriyi1]

Hi guys... I’m bringing the issue back again... what is better to use the short or long compression plugs... I would say straight away that a longer one would do a better distribution of loads around the fork and would increase the friction (although penalising the weight). Another question is, would you use carbon compound in order to again increase friction... additionally I’m asking this because of a “tantan (Chinese)” project and I’m concerned about the torques everywhere!!!


Sent from my iPhone using Tapatalk