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Stem digging in the steering tube

Old 04-28-22, 03:30 PM
  #1  
Redbullet
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Stem digging in the steering tube

Hello,

Grateful if somebody has a solution for the issue below (sorry for the bad quality sketch… )

It is about a road bike with steering tube diameter of 28.5 mm, carbon fiber.
Because of too long spacers area (35mm, changed to 30 mm), the edge of the stem slightly eroded the steering tube in the area marked with “A”. The erosion is about 0.1mm. I don’t think it is a critical decrease in resistance now, but, since the steering tube is not perfectly round anymore, it now generates successive loosening of the fork. In time, the stem would further “dig” in the tube, generating critical loss in carbon fiber resistance.
I am thinking that using another type of stem with a bigger clamping height (say 60mm instead of actual 41.8 mm) and removing corresponding spacers, would change the forces and solve the issue. But I did not find (yet) such a special stem.

How should I fix it? Of course, I would not like to increase the saddle to handlebar drop by only remove the spacers.

Thanks

Last edited by Redbullet; 10-17-22 at 03:06 PM.
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Old 04-28-22, 03:57 PM
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What you proposed -- buying a stem with higher stack height -- seems to be a good idea, but the problem is that most stems have an approximately 40 mm stack height.
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Old 04-28-22, 04:12 PM
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I would post some actual photos of what is going on.

If you are looking to be more upright you could consider a stem with higher rise if not what exactly is the goal.
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Old 04-28-22, 04:23 PM
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Buy the large version of this compression plug, so that the plug extends below the steerer clamp and supports the inside of the steerer. https://www.amazon.com/Neco-Headset-...8-2&th=1&psc=1
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Old 04-28-22, 04:29 PM
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Originally Posted by veganbikes
I would post some actual photos of what is going on.

If you are looking to be more upright you could consider a stem with higher rise if not what exactly is the goal.
He is not trying to get the handlebar higher. He is looking to keep the handlebar at about the same spot but replace his current stem with another stem with a greater stack height.
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Old 04-28-22, 04:32 PM
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I am not sure about what you are describing. I cannot picture in my mind how that is digging into the steer tube. The steer tube should be turning with the stem, and should not be able to do that to the tube, if everything is installed properly. Pictures of what you are concerned with would be a help. It does sound like it is going to be an issue, if it is not already. CF is good, strong frame/fork material until it is damaged. Depending on the location and the type of damage, it may look like it is ok, only to have it fail while riding. A failure in the steer tube is not a good thing. IME, all carbon steer tubes state that certain precautions need to be taken for safety reasons. Undo pressure in a small area is a lead in to failure.
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Old 04-28-22, 04:42 PM
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Is it really digging into and gouging the steerer tube or is it just a scratch?

A gouge might be worrisome. As another suggested, I'd get the star nut below that point and consider lowering the bars so the gouge is in the upper part of the stem clamp. Still, depending on how much it's gouged, I'd be a little bothered every time I rode.

I don't know what can be done for a carbon steerer that is damaged, so consider a new fork if you can afford it.
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Old 04-28-22, 04:58 PM
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Originally Posted by Iride01
Is it really digging into and gouging the steerer tube or is it just a scratch?

A gouge might be worrisome. As another suggested, I'd get the star nut below that point and consider lowering the bars so the gouge is in the upper part of the stem clamp. Still, depending on how much it's gouged, I'd be a little bothered every time I rode.

I don't know what can be done for a carbon steerer that is damaged, so consider a new fork if you can afford it.
Carbon fiber steer tubes do not use a star nut. They use and expanding plug. What was proposed above is always the best idea. Get an expanding plug that is long enough to support the stem clamp from inside the steer tube. I have no idea if that will solve what the OP thinks is the issue, but it's the best practice for a CF steer tube regardless.

I'm also having a hard time picturing the issue. I hope OP can provide a photo.
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Old 04-28-22, 05:37 PM
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I am thinking what the op is saying is that too many spacers were put on, so that the top of the steerer was below the top of the stem and that the stem rocked, digging into the steer tube.
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Old 04-28-22, 06:36 PM
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Originally Posted by SoSmellyAir
He is not trying to get the handlebar higher. He is looking to keep the handlebar at about the same spot but replace his current stem with another stem with a greater stack height.
Oh OK that is an odd one but I am curious to see photos from then.
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Old 04-28-22, 06:50 PM
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Carbon steerers can be compressed by the stem's clamping forces. Carbon doesn't like compressive forces as well as tension ones. I wonder if this is why the steerer has the "marks" on it. I wonder what torque level the stem clamp bolts were wound down to. If the steerer had no internal reinforcement (pressure plug) the stem would both not be well tightened around the compressing steerer and be more likely to drift up the steerer, loosening the headset preload.

But there are other reasons for a fork to feel "loose" that headset or stem ones. Andy
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Old 04-28-22, 07:04 PM
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I posted some Bianchi steerer photos in an older thread. It indicates the difference between normal stem clamp marks and a crushed carbon stem.

~~~

OP, you could lower the stem by 5mm with a half-height spacer (instead of the usual 10mm spacers.) And add another 5mm spacer above it so that the top cap still works. Maybe a different stem angle would be helpful.

This stem calculator will help pick from the available stem choices. (This calculator has been on the internet for years! very useful.)
https://yojimg.net/bike/web_tools/stem.php (note the https:// If I leave it off, defaulting to https:// it complains about a certificate.)

For example if you have 100mm at 5 degrees, and 30 mm of spacers:
(I used the example 73 degree head tube angle -- that's not critical with calculating a stem replacement like this.)

A 7 degree stem with 5 mm less spacers below is "close enough", making the bars just 1 mm lower than the original stem.


Last edited by rm -rf; 04-28-22 at 07:08 PM.
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Old 04-28-22, 08:47 PM
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Is the OP saying that the lower front edge of the steam scored a groove in the front side of the steerer? Would excessive weight on the bars with a long stem do this? Are there any rough spots of burrs at the edge of the steerer clamp? But then he's saying that the steerer isn't round anymore, implying that any damage to the steerer isn't localized to just the groove at the lower edge of the stem. If the steerer clamp has crushed the steerer and ovalized it to the point that the stem won't stay tight, I think the steerer is done.
If that's NOT what he's saying, and the problem is just the scoring at the edge of the steerer, he could just reduce his spacer stack by 5mm - would make little noticeable difference to saddle-to-bar drop, and would get the edge of the stem away from the scored area. I really don't like the sound of that steerer, though.
FWIW I have the same stem (110mm), sitting on ~20mm spacers on a 1 1/8" carbon steerer, with no issues. While I think that 35mm of spacers might be the upper end of what I'd use with a 1 1/8" CF steerer (and this is based solely on a rule of thumb, of indeterminate origin, that the spacer stack shouldn't exceed the CF steerer diameter), I don't think an extra 15mm of spacers that the OP used would result in what the OP is seeing.
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Old 04-28-22, 10:31 PM
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Originally Posted by squirtdad
I am thinking what the op is saying is that too many spacers were put on, so that the top of the steerer was below the top of the stem and that the stem rocked, digging into the steer tube.
Wait, I thought the top of the steerer tube is supposed to be about 2 mm below the top of the stem?
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Old 04-29-22, 04:34 AM
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Originally Posted by SoSmellyAir
Wait, I thought the top of the steerer tube is supposed to be about 2 mm below the top of the stem?
Many people don't like setting their bike up this way because it does reduce some of the stem's stability, which is probably even more critical with carbon steer tubes. With the stated scenario above, some would remove a spacer from below the stem, and install it above the stem instead. This ensures that 100% of the height of the stem clamp area is clamping steer tube, and the spacer above the stem gives enough compression clearance for the top cap. If one wanted a certain handlebar position, then a stem with a higher angle could be used to compensate for the lower mounting height.

I usually set my threadless cockpits up as you describe above, but I typically use shorter stems (which reduce leverage on the steer tube) and I don't own anything with carbon. All of my steer tubes are steel, and I imagine steel is much more resiliant and forgiving of this type of thing.
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Old 04-29-22, 04:38 AM
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[QUOTE=hokiefyd;22488679]Many people don't like setting their bike up this way because it does reduce some of the stem's stability, which is probably even more critical with carbon steer tubes. With the stated scenario above, some would remove a spacer from below the stem, and install it above the stem instead. This ensures that 100% of the height of the stem clamp area is clamping steer tube, and the spacer above the stem gives enough compression clearance for the top cap. If one wanted a certain handlebar position, then a stem with a higher angle could be used to compensate for the lower mounting height.


That is the way I prefer, especially with carbon tube. But either way, the tube needs to be a couple of mm below the top of the stem.

Last edited by delbiker1; 04-29-22 at 04:43 AM. Reason: add more info
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Old 04-29-22, 10:02 AM
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Originally Posted by SoSmellyAir
Wait, I thought the top of the steerer tube is supposed to be about 2 mm below the top of the stem?
I was not specific but, I was thinking a lot more than 2mm, enough so that the stem was not stable and causing wear, could also be over torque. All speculation without pics
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Old 04-29-22, 11:11 AM
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For carbon steerers, I thought it was preferred to let the steerer protrude above the stem and a narrow spacer be put on top to allow the cap to pull needed amount slack out of the bearings, or pre-load if you prefer.

For steel steerers I've read it's okay if the stem is above the top of the hole for the upper pinch bolt, but below the top of the stem by whatever is needed to take out the slack.
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Old 04-29-22, 01:52 PM
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Most forks come with instructions. Follow them.
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Old 04-29-22, 03:10 PM
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Thanks everybody for the answers.
Under normal variable pressure over the handlebar (see the sketch below), the elastic steerer will successively bent (imperceptibly) forward and recover, generating a concentration of pressure exactly at the edge of the stem. Bent and edge pressure will increase with the height of the spacers. It is not a surprise that modern CF bikes have very low (or zero) height of spacers. In my case, having 35mm of spacers made the edge of the stem to “dig” around 0.1 mm in the steerer, within a period of around 3 years (20-25000 km). I removed then one spacer and I got 30mm spacers height. But even at this height, the edge starts to “dig”. It is only a light scratch now, but it will increase with riding – and I want to avoid it.
I have a thick and long compression bolt. It makes a good job in helping preloading and maybe it can assure a short period for braking in case of steering tube failure, but I think it does not really make the steerer to bent less.

A stem with higher stack height would simulate the situation of lower spacers height and decrease the bent and pressure at the edge.
A further decrease with 5mm in spacers height would increase too much the saddle to handlebar drop… which I am trying to avoid, as it is already 6-7 cm…

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Old 04-29-22, 05:15 PM
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[QUOTE=delbiker1;22488681]
Originally Posted by hokiefyd
Many people don't like setting their bike up this way because it does reduce some of the stem's stability, which is probably even more critical with carbon steer tubes. With the stated scenario above, some would remove a spacer from below the stem, and install it above the stem instead. This ensures that 100% of the height of the stem clamp area is clamping steer tube, and the spacer above the stem gives enough compression clearance for the top cap. If one wanted a certain handlebar position, then a stem with a higher angle could be used to compensate for the lower mounting height.


That is the way I prefer, especially with carbon tube. But either way, the tube needs to be a couple of mm below the top of the stem.
To the bolded- Many carbon fork brands want the top of the steerer to slightly extend above the top of the stem, to insure that the stem is clamping completely on the steerer far enough from the end to reduce any cracking/collapse type failure. A short, often 5mm spacer sirs atop the stem. It is at this point, with that extra 5mm spacer on top, that the "steerer must be 2 to 3mm below the top" should be at for many carbon forks. Andy
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Old 04-30-22, 01:37 PM
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Mine has a special spacer above and the steerer extends around 2mm above the stem.

I was thinking about a workaround for my issue, although a little expensive and not very elegant (see the sketch below):
Change the actual 28.6 to 31.8 mm stem and use two adapters like This, in such a way that they meet in the middle of stem clamping area. The first adaptor will go down around 20 mm below the edge of the stem. It should protect the steerer from stem edge and distribute the forces somehow similar with the situation of a longer stack stem and around 10mm spacer.
Would this be a solution to my issue? Would it create other issue? Should I use higher torque than recommended 5Nm for steerer clamping, since I use adaptors?
Thanks.

Last edited by Redbullet; 10-17-22 at 03:08 PM.
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Old 04-30-22, 01:50 PM
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I think you are looking for solutions before knowing the cause of the problem. The link to the adapters takes me to Ritchey but the page that comes up is a " Page not found" with numerous reasons for why. One being the page is outdated. Your explanation makes no sense to me, FIW
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Old 04-30-22, 02:02 PM
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Originally Posted by delbiker1
I think you are looking for solutions before knowing the cause of the problem. The link to the adapters takes me to Ritchey but the page that comes up is a " Page not found" with numerous reasons for why. One being the page is outdated. Your explanation makes no sense to me, FIW
I think the reason is that I have too big height of spacers (35 and then 30mm - not recommended for CF) and this allows steerer to bent too much, which leads to high concentration of forces.
The link should work: https://eu.ritcheylogic.com/eu_en/bi...m-shim-adaptor .
Yo can also google for "ritchey stem shim adaptor".

Thanks.
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Old 04-30-22, 02:10 PM
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Originally Posted by Redbullet
It is not a surprise that modern CF bikes have very low (or zero) height of spacers. In my case, having 35mm of spacers made the edge of the stem to “dig” around 0.1 mm in the steerer, within a period of around 3 years (20-25000 km). I removed then one spacer and I got 30mm spacers height. But even at this height, the edge starts to “dig”. It is only a light scratch now, but it will increase with riding – and I want to avoid it.
Are you confusing the slammed stem phenomena with the maximum spacer stack height allowed?

My 5 year old Cannondale Synapse (is it modern?) allows a maximum 55 mm of spacers (including the headset top cap) under the stem and has a stated weight limit of 275 lbs. (rider) + 10 lbs. (luggage). I have never seen a mark on the steerer from the stem, either when flipping the original stem or when replacing it with a different one. Either my steerer is over built, or your steerer was slightly scored (~ 0.1 mm deep) by the installation of the stem. Make sure that the expander is properly installed -- more on this below -- and the stem bolts are tightened to the correct torque (usually 5 nm or 6 nm), and diligent monitor to see if the scoring gets deeper.

Originally Posted by Redbullet
I have a thick and long compression bolt. It makes a good job in helping preloading and maybe it can assure a short period for braking in case of steering tube failure, but I think it does not really make the steerer to bent less.
The compression bolt sets the preload by pulling up on the steerer relative to the frame, spacers, stem, and top cap. The expander needs to be installed at the proper depth within the steerer to reinforce the section clamped by the stem.

Originally Posted by Redbullet
Mine has a special spacer above and the steerer extends around 2mm above the stem.

I was thinking about a workaround for my issue, although a little expensive and not very elegant (see the sketch below):
Change the actual 28.6 to 31.8 mm stem and use two adapters like This, in such a way that they meet in the middle of stem clamping area. ...
Overcomplicating and weakening the stem to steerer connection is really a bad idea. Why don't you just buy a longer stem with a greater angle which can be installed lower on the steerer, which would keep your handlebar at approximately the same spot?
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