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Stack height on CF steerer?

Old 01-01-13, 05:20 PM
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AlphaDogg
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Stack height on CF steerer?

I was given a bike temporarily (which could turn into permanently), and the owner gave me the green light to make adjustments so it'll fit me. It's a really nice Ti Merlin with CF seatstays and a CF fork from the early 2000's. I changed the stem out and lowered it (borrowed a torque wrench from the LBS and set it at 6Nm), but the steerer is really long, so I had to put a lot of spacers on top. There's 35mm of spacers above the stem and 15mm of spacers below it. CF scares me, so I wanna know if how it's set up is safe. If I end up keeping it, I'll definitely cut the steerer.

Here are some pictures:

A picture of the steerer/stem area:


Pictures of the top cap/bolt:




A picture of the inside of the steerer:


Note there's some sort of expansion plug inside there. The top of the expansion plug is above where the stem is clamped.
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Old 01-01-13, 05:31 PM
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The expansion plug should be centered on the stem. The stem clamp bolts only need to be tight enough for the stem to stay put under hard steering imputes. Did you apply any carbon paste? Don't worry about the spacers above the stem, they're along for the ride and to proving compression transfer. In fact once the stem is set (and the headset adjustment is done) the top cap and above spacers could be removed without concers.
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Old 01-01-13, 05:31 PM
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The setup should be fine, just don't go nuts tightening the stem clamp bolts. 5Nm is plenty.
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Old 01-01-13, 05:32 PM
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Anything above the stem doesn't count except for the risk of getting impaled in a crash. I prefer to keep the stack below the stem at 20-25mm max, and you're well within that. I've seen people with 40-50mm under the stem, and haven't heart (1st hand) of any failures, but of course it depends on how you ride. If you tend to work the bars hard when climbing or sprinting, or ride on lots of Pave, then I suggest you keep the stack short just in case.

BTW- there's no need to ever cut the fork, but cosmetics, or wanting to avoid being impaled may have you cutting it down after you've found your preferred stem height and ridden with a while to confirm.
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Old 01-01-13, 05:37 PM
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Originally Posted by Andrew R Stewart View Post
The expansion plug should be centered on the stem. The stem clamp bolts only need to be tight enough for the stem to stay put under hard steering imputes. Did you apply any carbon paste? Don't worry about the spacers above the stem, they're along for the ride and to proving compression transfer. In fact once the stem is set (and the headset adjustment is done) the top cap and above spacers could be removed without concers.
Thanks. I forgot to put on any cf assembly paste, but the stem stays put at 6Nm. It was a click type torque wrench, and it didn't have a setting for 5Nm, so I went with 6Nm.
Originally Posted by DaveSSS View Post
The setup should be fine, just don't go nuts tightening the stem clamp bolts. 5Nm is plenty.
I used a torque wrench as mentioned.
Originally Posted by FBinNY View Post
Anything above the stem doesn't count except for the risk of getting impaled in a crash. I prefer to keep the stack below the stem at 20-25mm max, and you're well within that. I've seen people with 40-50mm under the stem, and haven't heart (1st hand) of any failures, but of course it depends on how you ride. If you tend to work the bars hard when climbing or sprinting, or ride on lots of Pave, then I suggest you keep the stack short just in case.

BTW- there's no need to ever cut the fork, but cosmetics, or wanting to avoid being impaled may have you cutting it down after you've found your preferred stem height and ridden with a while to confirm.
Thanks! I hate the aesthetics of a long stack above the stem, so I will definitely cut it if I keep the bike. I don't think I work the bars hard. I usually stay seated and work the quads when climbing, but I sometimes do a bit of out of saddle sprinting. Before I lowered the stem, the stack height below the steerer was 30mm.

How long are expansion plugs usually? I want to know if there is enough of the plug supporting the stem clamp.
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Old 01-01-13, 05:40 PM
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For 1" carbon steerers the usual recommended maximum spacer stack under the stem is about 25 mm. For a 1-1/8" carbon steerer, the most common maximum spacer recommendation is 40 mm but Easton permits 50 mm. You are well within these limits. As noted, what's above the stem is meaningless from a structural standpoint. It just looks odd if it's tall.

The expansion plug isn't needed to support the stem, it just acts as a anchor for the adjusting bolt in most cases.
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Old 01-01-13, 05:47 PM
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Originally Posted by HillRider View Post
For 1" carbon steerers the usual recommended maximum spacer stack under the stem is about 25 mm. For a 1-1/8" carbon steerer, the most common maximum spacer recommendation is 40 mm but Easton permits 50 mm. You are well within these limits. As noted, what's above the stem is meaningless from a structural standpoint. It just looks odd if it's tall.
Thanks. I thought I read somewhere that large stacks of spacers above the stem can be bad. Logically, it would have something to do with the expansion plug being too high in relation to the stem. My concern is that there isn't enough of the expansion plug supporting the stem clamp. Also, the steerer is 1-1/8".
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Old 01-01-13, 05:50 PM
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Originally Posted by AlphaDogg View Post

How long are expansion plugs usually? I want to know if there is enough of the plug supporting the stem clamp.
Doesn't matter. There are some who feel that the plug must be within the stem, but I don't thing it makes a difference at all unless you over-tighten the plug like crazy. If you decide you want to push the plug deeper and have it within the stem, all you need is a screw long enough to reach it. Save the old screw for when you cut the stem.

BTW- nobody does it this way (probably because it isn't needed) but the only place the plug would make a structural difference is halfway down into the headset. This would buttress the steerer at the fulcrum of the bending moments, where failure is most likely.
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Old 01-01-13, 05:52 PM
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Originally Posted by AlphaDogg View Post
Thanks. I thought I read somewhere that large stacks of spacers above the stem can be bad. ..
They are bad, they look like crap, and can increase the risk of injury in a sensitive area if you crash. Whenever I see bikes set up that way I figure the owners already have as many children as they want.
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Old 01-01-13, 05:58 PM
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Originally Posted by FBinNY View Post
They are bad, they look like crap, and can increase the risk of injury in a sensitive area if you crash. Whenever I see bikes set up that way I figure the owners already have as many children as they want.
I'm still in high school, and thus have no children. Every time in the past that I've taken a fall, I've just fallen on my side with my feet clipped in to the pedals. I've never had the cockpit of the bike come in contact with my groin, so I think I'll be alright. Plus, this is only temporary.

As a side note, the tires on it were trash. The rear has flat spots with cords showing through from skids and the front has a sidewall tear. It had a thorn proof tube in the front and a tire liner in the rear. No wonder the bike was so heavy! I'm putting my GP4000S's from my own bike on it so I can take it for a ride. I'd swap wheels and cassettes with my own bike, but I wanna ride the (lightweight when compared to my own FSA wheelset) Mavic Cosmos wheels.
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Old 01-02-13, 10:53 AM
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I haven't seen anybody mention this, but in the second pic down, the cap appears to have a long extension which protrudes down into the steerer and will require locating the expansion plug lower in the steerer. I've only ever seen caps that protrude a very short distance into the steerer. How closely does that cap extension fit into the steerer? Is it conceivable it was intended to help protect the steerer from being crushed by the stem?
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Old 01-02-13, 05:29 PM
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Originally Posted by Looigi View Post
I haven't seen anybody mention this, but in the second pic down, the cap appears to have a long extension which protrudes down into the steerer and will require locating the expansion plug lower in the steerer. I've only ever seen caps that protrude a very short distance into the steerer. How closely does that cap extension fit into the steerer? Is it conceivable it was intended to help protect the steerer from being crushed by the stem?
It has about 1/10mm of play when inserted into the steerer. Sure, I guess it's conceivable that it adds a little support to the steerer from being crushed, but not a whole lot.

I took the bike for a ride today, and it rides beautifully! The steering was way different than what I'm used to. It's gotta have something to do with the fact that its geometry is different than my Fuji's racing geometry. It's not horrible, but it'll take a lot of getting used to if I end up keeping the bike. I lowered the stem yet again, leaving the stack height below it at essentially 0mm and the stack above it at 50mm. That periscope sure is ugly!
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