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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 01-06-14, 08:01 PM   #1
Crescent Cycle
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Minimum spacers for (safe) stem slamming?

I know you can get a special dust cover to get a stem really slammed, but what is the minimum recommended amount of spacers to prevent steerer damage on a carbon steerer?

5mm top spacer
40mm stem
5mm spacer
5mm cone spacer

Trying to compare the HT length of a threaded frame to a threadless frame. I know some lugs have a taller head lug for 1 1/8 steerers. Minimum spacers would seem to take up most of the difference between an external cup threadless and the locknut on a threaded headset.
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Old 01-06-14, 11:02 PM   #2
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No spacers at all on my 9/8" full carbon fork. On another bike, I plan to run 0mm of spacers on a sub-400g 1" full carbon fork when I get hold of one.

I'm not anticipating any explosions.

YMMV though, particularly if you're the beefy sprinter type.
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Old 01-06-14, 11:13 PM   #3
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Trek wants a 5mm spacer on top of the stem, and it's probably not a bad idea. I don't think there is a problem with no spacer under the stem unless the stem doesn't sit right without it
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Old 01-06-14, 11:39 PM   #4
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Some makers say their carbon-steerer forks, or a particular model of such, don't require a spacer above the stem.

It could be related to wall thickness of the steerer. But the expander is a factor too - some forks use a plug that's bonded in; I'd say this would likely eliminate any need for protruding steerer.

I guess because we're talking about what's basically a reinforced plastic, the potential issue here is the compression of the steerer by the stem's clamp (hence compression plugs), and with the steerer ending inside the clamp, it could be squashed into a slightly conical shape, obviously a Bad Thing. So with a spacerless carbon steerer I tighten the upper bolt a tad less and the lower one a tad more.
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Old 01-07-14, 12:20 AM   #5
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Why are any spacers required, unless you need to compensate for a "long" steerer, and don't want to cut it?
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Old 01-07-14, 12:57 AM   #6
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I could have sworn I read some manufacturer blame a steerer explosion because of lack of spacers under the stem increasing stresses.

And from what I understand not running a spacer on top of a carbon steerer voids almost every fork warranty and increases likelihood of cracking.
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Old 01-07-14, 06:01 AM   #7
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I have never heard of a lack of spacers under the stem causing a problem. The problem is too many spacers under the stem allowing the steerer to flex above the headtube and causing damage at that point. The reason for a spacer above the stem is to provide full contact between the steerer and the stem to prevent compression damage to the top of the stem.
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Old 01-07-14, 06:27 PM   #8
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.. the stem fully around the carbon steerer , then having the HS preload adjustment gap,
half of the spacer above.. it's thickness, would seem the prudent plan.


Quote:
I could have sworn I read some manufacturer blame a steerer explosion
because of lack of spacers under the stem increasing stresses.
well this is when you foot note that reference ,for others to read,
and make their interpretation..

simple lower leverage would suggest shorter the better ..
taller a steel steerer has benefits. just minimum weight is not paramount.

Last edited by fietsbob; 01-07-14 at 06:34 PM.
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Old 01-13-14, 12:48 PM   #9
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From Trek
Quote:
2) Always use spacers above and below the stem. Although less obvious than correct torque, a minimum of 5mm and a maximum of 40mm spacers under the steerer, plus a 5mm spacer above the stem are required. Riders should factor in these spacers when sizing their bike.
Not sure if that includes the cone or not.
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Old 01-16-14, 11:01 AM   #10
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Quote:
Originally Posted by Crescent Cycle View Post
From Trek

Not sure if that includes the cone or not.
That quote above from a big company like Trek seems pretty funny to me when they all sell top end bikes with a limited number of fixed frame sizes. The quote ignores that the buyer may also be concerned with top tube length (or other specs like ST angle which changes with size) and only one top tube length (and one ST angle) is available with each head tube height. Limited number of fixed sizes does not allow much "sizing" for head tube length.
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Old 01-16-14, 02:00 PM   #11
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If You are in the slammed low, short carbon fork Niche , good luck with that . not everyone is ..
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Old 01-16-14, 06:11 PM   #12
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Well the primary reason why I would even consider custom is to get a range of attributes that I can't get from a mass produced frame. That includes a sub 500mm stack height including headset and all spacers that can fit standard forks and standard 700c wheels. If I just wanted old world craftsmanship with a standard geometry, I would just buy a vintage old world frame. I thought that was the point of custom. You know, to get a frame not for everyone.
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