Above the stem
11-13-22, 03:23 PM
#1
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Above the stem
What is the approved measurement for the amount of spacer above the stem?
As my core strength is improving I’ve started to move the stem down on the steerer tube, right now I am at a 10mm spacer above and 23mm below. I don’t want to cut the steerer more than once and think I’ll probably lower it some more but a don’t want to commit a BF faux pas.
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As my core strength is improving I’ve started to move the stem down on the steerer tube, right now I am at a 10mm spacer above and 23mm below. I don’t want to cut the steerer more than once and think I’ll probably lower it some more but a don’t want to commit a BF faux pas.
.
11-13-22, 03:50 PM
#2
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If you are positive you like your position and positive you will not be selling the bike, enough for one small spacer, 5mm.
At 10mm you are close enough that only a meanie would say “down periscope” or “chimney” to you so I would leave it alone for now.
At 10mm you are close enough that only a meanie would say “down periscope” or “chimney” to you so I would leave it alone for now.
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11-13-22, 04:19 PM
#3
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Most would say no spacer above or a 5mm spacer above at the most is the perfect look (and I tend to agree).
That said, I always stick with a 10mm above just in case I ever fancy/need more height at some point. Stick with what you've got. If you do lower later on, you can cut then.
That said, I always stick with a 10mm above just in case I ever fancy/need more height at some point. Stick with what you've got. If you do lower later on, you can cut then.
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11-13-22, 04:24 PM
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I moved my stem down and put the spacer over it. I don’t mind the look and it’s isn’t hurting anything by being there.
11-13-22, 04:50 PM
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A 2mm spacer is generally enough, and no spacers will work perfectly if the top cap is designed for it; the important bit is that the top cap can push "against" the stem.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
11-13-22, 05:09 PM
#6
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Originally Posted by Branko D
A 2mm spacer is generally enough, and no spacers will work perfectly if the top cap is designed for it; the important bit is that the top cap can push "against" the stem.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
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11-13-22, 05:43 PM
#7
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We both ride slammed stems and all mechanics I ever spoke to when I get these chopped suggested to leave a 5mm spacer on top.
11-13-22, 06:10 PM
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Originally Posted by yaw
We both ride slammed stems and all mechanics I ever spoke to when I get these chopped suggested to leave a 5mm spacer on top.
If your bike comes with a top cap with an integrated spacer, or the stem and top cap are designed not to need one (many Specialized bikes) there's absolutely no need for 5mm spacer on top.
Originally Posted by Shadco
Not sure this makes sense to me, the steerer had the stem at the top with just enough gap to allow for proper preload and 33mm of spacers below. If I rearrange the order and move a 10mm spacer above the stem with a long enough compression plug what difference would it make? The compression is 40mm long and reaches below the top bearing.
.
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Last edited by Branko D; 11-13-22 at 06:17 PM.
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11-13-22, 07:43 PM
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Originally Posted by Branko D
A 2mm spacer is generally enough, and no spacers will work perfectly if the top cap is designed for it; the important bit is that the top cap can push "against" the stem.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
Anything more than 5mm is unnecessary, and tall spacer stacks above the stem prevent the compression plug (depending on it's length) from supporting the stem from inside, so with a spacer stack you will be clamping unsupported carbon, which is a bad idea and not how it was designed to work.
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11-14-22, 01:05 AM
#10
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Originally Posted by tempocyclist
Most would say no spacer above or a 5mm spacer above at the most is the perfect look (and I tend to agree).
That said, I always stick with a 10mm above just in case I ever fancy/need more height at some point. Stick with what you've got. If you do lower later on, you can cut then.
That said, I always stick with a 10mm above just in case I ever fancy/need more height at some point. Stick with what you've got. If you do lower later on, you can cut then.
Setting it up so the entire stem is below the top of the steerer tube means the stems full clamping force is completely on the steerer tube and none of it is pinching and pushing in the top of the steerer tube.
...or am I misunderstanding what you posted?
11-14-22, 01:37 AM
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Originally Posted by mstateglfr
No spacer above means the stem is tightened and the top of the steerer tube is impacted by the tightened stem. That seems less than ideal.
Setting it up so the entire stem is below the top of the steerer tube means the stems full clamping force is completely on the steerer tube and none of it is pinching and pushing in the top of the steerer tube.
Setting it up so the entire stem is below the top of the steerer tube means the stems full clamping force is completely on the steerer tube and none of it is pinching and pushing in the top of the steerer tube.
Not ideal
You'll notice the top (black) part of the compression plug doesn't actually expand, so without a spacer on top, the top bolt of the stem will, depending on location, clamp a partially unsupported bit. This type of steerer plug is also why a stack of spacers above is unwise if you haven't checked what sort of compression plug you've got; it's really short, so if you put 20mm of spacers above, the bottom bolt will clamp an unsupported bit. It's not a very good design, but it gets used.
This one is completely fine structurally without a spacer on top, and is longer meaning that with a spacer or two on top you'll still be fine nevertheless:
A much better design.
Last edited by Branko D; 11-14-22 at 03:33 AM.
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11-14-22, 07:14 AM
#12
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Originally Posted by Branko D
If we want to talk about structural integrity, the area where the bolts are must be supported adequately from inside by a compression plug for everything to be ideal. The reason why it's safer to recommend everyone leave a 5mm spacer are compression plugs like this one:
Not ideal
You'll notice the top (black) part of the compression plug doesn't actually expand, so without a spacer on top, the top bolt of the stem will, depending on location, clamp a partially unsupported bit. This type of steerer plug is also why a stack of spacers above is unwise if you haven't checked what sort of compression plug you've got; it's really short, so if you put 20mm of spacers above, the bottom bolt will clamp an unsupported bit. It's not a very good design, but it gets used.
This one is completely fine structurally without a spacer on top, and is longer meaning that with a spacer or two on top you'll still be fine nevertheless:
A much better design.
Not ideal
You'll notice the top (black) part of the compression plug doesn't actually expand, so without a spacer on top, the top bolt of the stem will, depending on location, clamp a partially unsupported bit. This type of steerer plug is also why a stack of spacers above is unwise if you haven't checked what sort of compression plug you've got; it's really short, so if you put 20mm of spacers above, the bottom bolt will clamp an unsupported bit. It's not a very good design, but it gets used.
This one is completely fine structurally without a spacer on top, and is longer meaning that with a spacer or two on top you'll still be fine nevertheless:
A much better design.
The wall thickness on my steerer tube is also at least 3/16s” thick carbon.
.
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11-14-22, 09:56 AM
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Being very old and riding a fairly amount of drop, I have left myself a cm in case of a sudden attack of decrepitude.
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11-14-22, 11:39 AM
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If you are happy with just putting the spacers you take off the bottom to lower the stem on top, then there is no need to cut the stem at all. It's not like I'm going to pass you on the road and that's the thing I'm going to notice about you and your bike.
But if you do have to cut it, and your steerer is carbon fiber, then the general advice is that the steerer should be at or above the top of the stem slightly and a spacer on top the stem. A 2 mm spacer is more than enough if it allows enough slack to be taken out of the headset bearings without the steerer tube touching the cap.
But if you do have to cut it, and your steerer is carbon fiber, then the general advice is that the steerer should be at or above the top of the stem slightly and a spacer on top the stem. A 2 mm spacer is more than enough if it allows enough slack to be taken out of the headset bearings without the steerer tube touching the cap.
11-15-22, 07:15 AM
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As long as your compression plug covers the stem area, you're fine. Aesthetically speaking, the less the better, that's for sure.
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11-17-22, 09:15 AM
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Obscure trivia: Cannondale's "SI Integrated" carbon forks & headsets & expansion plugs etc (the hardware for which iirc is OEMd by FSA) explicitly state that you should not use any spacers above the stem. I haven't looked at their design to figure out why they are so emphatic about this point, but it's slathered all over their installation guides and owner's manuals enough times that I'm sure there's a reason either their design team, or their legal team, insisted this be stated unequivocally.
11-17-22, 09:27 AM
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Originally Posted by Bob Ross
Obscure trivia: Cannondale's "SI Integrated" carbon forks & headsets & expansion plugs etc (the hardware for which iirc is OEMd by FSA) explicitly state that you should not use any spacers above the stem. I haven't looked at their design to figure out why they are so emphatic about this point, but it's slathered all over their installation guides and owner's manuals enough times that I'm sure there's a reason either their design team, or their legal team, insisted this be stated unequivocally.
If this is the design:
https://images.bike24.net/media/366/i/mb/95/d5/51/cannondale-kp017-si-expander-by-fsa-1136668.jpg
I can see why. The expansion plug is very short so any spacers above and you are claimping an unsupported CF steerer, and the mechanism is made to preload the bearings without spacers.
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11-18-22, 05:51 PM
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Originally Posted by Bob Ross
... Cannondale's "SI Integrated" carbon forks & headsets & expansion plugs etc (the hardware for which iirc is OEMd by FSA) explicitly state that you should not use any spacers above the stem. I haven't looked at their design to figure out why they are so emphatic about this point, but it's slathered all over their installation guides and owner's manuals enough times that I'm sure there's a reason either their design team, or their legal team, insisted this be stated unequivocally.
Originally Posted by Branko D
If this is the design:
https://images.bike24.net/media/366/...sa-1136668.jpg
I can see why. The expansion plug is very short so any spacers above and you are claimping an unsupported CF steerer, and the mechanism is made to preload the bearings without spacers.
If this is the design:
https://images.bike24.net/media/366/...sa-1136668.jpg
I can see why. The expansion plug is very short so any spacers above and you are claimping an unsupported CF steerer, and the mechanism is made to preload the bearings without spacers.
The Synapse also allows a generous 55 mm of spacers under the stem; I am using 50 mm (with a -8 degree stem). I have not seen any other bike with a carbon steerer which allows > 40 mm of spacers under the stem.
However, interestingly, in the manual 2017-2020 version of the Synapse, oms cd bk rd synapse disc en r1 134911.pdf (cannondale.com), the Compression Assembly does not support the top stem bolt, only the bottom stem bolt. See page 10.
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