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Cutting carbon steerer tube
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Road bike stem is slammed. I want to cut the steerer tube down (to look pro). I’ve cut these on every bike I’ve had but always followed the spacer on top of the stem rule for carbon.

Anyway know if that rule is hard and fast? (I’m not worried about resale. And yes it’s my fit - looking pro is just a bonus :-)
Will it grind away without the spacer on top of stem?
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Re: Cutting carbon steerer tube [GreenBoy] [ In reply to ]
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5mm on top...looks good.

Besides, rule 45 - http://www.velominati.com/the-rules/
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Re: Cutting carbon steerer tube [GreenBoy] [ In reply to ]
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I dont believe it has any technical function besides giving you some extra room in case you change the stem at some point and the new one happens to be a bit taller.
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Re: Cutting carbon steerer tube [GreenBoy] [ In reply to ]
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It's your bike, cut away. They're rare in my experience but I've seen 2 cases on the bung/star nut substitute being bonded inside which would screw with any effort to cut it down but otherwise its easy. Main reason not to and stick with the spacer is for when you get older/less flexible and need just that little bit more without buying a stupid looking steep angle stem. I've known a number of people who after a serious crash or injury that took them off the bike for a time and into rehab had to raise their stem till they got back into form.
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Re: Cutting carbon steerer tube [dfroelich] [ In reply to ]
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These are awesome. Thanks for sharing.
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Re: Cutting carbon steerer tube [Fuzzybunnies] [ In reply to ]
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Well, I'm in my 40s is that old yet? :-)
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Re: Cutting carbon steerer tube [GreenBoy] [ In reply to ]
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The reason I've been given, is that you want to not have the open end of the steerer tube right where the stem clamp is applying a lot of pressure. In the case of a very thin wall steerer, and someone that cranks on the stem clamp a little too much, the steerer could hypothetically get crushed there. Having to stack the extra spacer requires you to extend the steerer a couple of millimeters above the stem, which increases the safety margin for that kind of failure.

Things are probably better now that people have generally figured out how to design with carbon fiber, and companies like Cervelo incorporated the glue-in starfangle nut assembly, which strengthens that area. But the basic physics there haven't changed.

Less is more.
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Re: Cutting carbon steerer tube [Big Endian] [ In reply to ]
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Big Endian wrote:
The reason I've been given, is that you want to not have the open end of the steerer tube right where the stem clamp is applying a lot of pressure. In the case of a very thin wall steerer, and someone that cranks on the stem clamp a little too much, the steerer could hypothetically get crushed there. Having to stack the extra spacer requires you to extend the steerer a couple of millimeters above the stem, which increases the safety margin for that kind of failure.

Yep. I got a used bike that was cut a bit too low, and my top bolt was just above the top of the steerer tube and it ended up cracking after a few weeks. Had to replace the fork.
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Re: Cutting carbon steerer tube [GreenBoy] [ In reply to ]
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I always leave a small spacer on top of the stem, as I've see a steerer tube crack when it was cut too low and the stem was a few mm above the tube. It created too much pressure on the back side of the tube and it crack and crushed it in.


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Re: Cutting carbon steerer tube [Benv] [ In reply to ]
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Benv wrote:
I dont believe it has any technical function besides giving you some extra room in case you change the stem at some point and the new one happens to be a bit taller.

As mentioned in the posts above, actually the 5mm spacer above the stem does indeed have a quite important function.

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Re: Cutting carbon steerer tube [DarkSpeedWorks] [ In reply to ]
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If I read the posts above correctly they are all cases of the fork being cut too short so it's not even long enough to fully fit the stem.
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Re: Cutting carbon steerer tube [Benv] [ In reply to ]
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Benv wrote:
If I read the posts above correctly they are all cases of the fork being cut too short so it's not even long enough to fully fit the stem.

No, even if the steer tube is cut right for "typical" mounting (2-3 mm below stem top to allow space for top cap to fit on stem), doing this for carbon steerer tubes is not recommended by nearly all manufacturers/sellers.

Any tube is hugely weaker at the very end of the tube to crushing forces. Solution? Extend the tube slightly (i.e., enough to fit a 5mm steer tube spacer) and the strength under the stem clamp area is sufficient to avoid cracking.

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook

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Re: Cutting carbon steerer tube [dfroelich] [ In reply to ]
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dfroelich wrote:
5mm on top...looks good.

Besides, rule 45 - http://www.velominati.com/the-rules/

Yeah, but rule 42 put me off.
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Re: Cutting carbon steerer tube [DarkSpeedWorks] [ In reply to ]
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DarkSpeedWorks wrote:
Benv wrote:
If I read the posts above correctly they are all cases of the fork being cut too short so it's not even long enough to fully fit the stem.


No, even if the steer tube is cut right for "typical" mounting (2-3 mm below stem top to allow space for top cap to fit on stem), doing this for carbon steerer tubes is not recommended by nearly all manufacturers/sellers.

Any tube is hugely weaker at the very end of the tube to crushing forces. Solution? Extend the tube slightly (i.e., enough to fit a 5mm steer tube spacer) and the strength under the stem clamp area is sufficient to avoid cracking.

Other solution is using stems with one bolt clamping system, for instance 3T ARX II.
In terms of whether the spacer above the stem can have any technical function, putting aside what was mentioned in previous posts, in some cases it is required by expander-top cap system.

And.... 3mm looks better than 5mm ;)
Last edited by: 1415chris: Jun 3, 18 23:56
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Re: Cutting carbon steerer tube [1415chris] [ In reply to ]
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For example, Cannondale wants it flush. Call your company’s customer service line and ask.

It’s also a function of which expander wedge you are using. Generally speaking you don’t want the expander wedge to end where the stem ends (stress riser). Each company designs and tests their fork with a specific expander wedge in mind.
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