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I am building my C50 over the next month. I have a question hoping this forum can help. The Colnago Star fork comes with aluminium expander plug (ITM). I have figured out how it works but I like comments on where is the appropriate position to place it, relative to the clamp column of the stem.

The logical position is to center the expander piece to the clamp column of the stem. But this position sets the upper wedge above the stem. Thus requiring 10mm spacer on the top for the headset cap. I have included a drawing of this setup.

If I set the top of the wedge 6-10mm below the top of the stem, no spacers are required on top of the stem. However, there is no reinforcement along the upper portion (10mm) of the clamp.

So for the builders out there, where do you set the expander?
 

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tmluk said:
I am building my C50 over the next month. I have a question hoping this forum can help. The Colnago Star fork comes with aluminium expander plug (ITM). ... If I set the top of the wedge 6-10mm below the top of the stem, no spacers are required on top of the stem. However, there is no reinforcement along the upper portion (10mm) of the clamp.
I have a 2004 Dream with a Force Fork (1” steerer tube) and Chorus headset parts, including the Campy “star nut” that’s used in both the Chorus and Record groups. Star nuts are structurally incapable of providing any support for the steerer tube walls as the stem clamp is tightened down. Also, I’m doing this from memory, but I think that the wall of the Force Fork carbon steerer tube is about an eight of an inch thick. In compression, these walls are very strong, and shouldn’t need any support at all. Your Star fork may be different, but I can’t imagine that it isn’t designed and build in a way that it can’t accommodate the standard Campy set up. I’d set the plug down so that it its below the top edge of the steerer tube.
 

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tmluk said:
The logical position is to center the expander piece to the clamp column of the stem. But this position sets the upper wedge above the stem. Thus requiring 10mm spacer on the top for the headset cap.
I build my bikes with a 10mm spacer on top to center the expander clamp between the
stem mounting bolts (Deda stem). IMO, the tightening torque for my stem to a CF steerer
tube is a little less for proper retention. Its also more symmetrical from a mechanical perspective.
 

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i did the same thing...also has the advantage of a little extra room on the steering tube so you can move the stem up if either you want it higher over time or you screw up the first time you cut it.
 

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just set mine up as you describe, had the same concerns, so after reading up on as many mfr insructions as i could i called tom at gvh bikes to settle the bet...he confirmed what we see here in your dwg as all correct, and per his experience gave the green light. the carbon steer tube onna star fork is not prone to crushing, and the expander plug we are using actually covers more internal area than the "top cap adjustable compression plugs", as they only engage with the lower portion of the tube relative to the stem.

so all is good.

a decent lbs mech told me he actually believes the plug beefs up the area to prevent crushing, but this would only be true if the stem clamp bolts torque was excessive to my mind.

as for the spacer on top, the latest is that the benefit for this is flexibility for adjustment rather than preventing damage. this is what is being taught at bike mech school, and is the accepted truth for *today's* cf steerers.

"don't worry, it's engineered"
-structural eng professor, somewhat tongue in cheek perhaps.




tmluk said:
I am building my C50 over the next month. I have a question hoping this forum can help. The Colnago Star fork comes with aluminium expander plug (ITM). I have figured out how it works but I like comments on where is the appropriate position to place it, relative to the clamp column of the stem.

The logical position is to center the expander piece to the clamp column of the stem. But this position sets the upper wedge above the stem. Thus requiring 10mm spacer on the top for the headset cap. I have included a drawing of this setup.

If I set the top of the wedge 6-10mm below the top of the stem, no spacers are required on top of the stem. However, there is no reinforcement along the upper portion (10mm) of the clamp.

So for the builders out there, where do you set the expander?
 
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