I am in the process of building up a Colnago Pista with a Cinelli Alter stem. The problem is that with the stem tightened all the way down it still slips on the steerer tube. According to the instructions you should use 13 Nm torque which we have done. Also it seems like the threads could get stripped out if the bolts are tightened any more. This is a brand new unused stem. My bike tech said he has checked the measurements on both the stem and fork and said they look to be within the specs. I found where someone else was having the same issue and ended up using a can as a shim to get it working here https://www.bikeforums.net/singlespee...stem-help.html

Any ideas?

carbon assembly paste

+1 A traction paste will give you more grip with less clamping force. Since the steerer is CF, you want to avoid the pastes that use abrasive grit, and look for one that uses rubber or PVC particles for grip.

However, just out of curiosity, how tight are you trying to get this?

Steering forces are very low, so there's no need to get a stem so tight that it won't twist if you force it while holding the wheel between your legs. BITD we had an informal standard for stuff like this which we called "race tight". That was tight enough to meet all practical needs, yet not so tight that it wouldn't slip in a crash. A stem slipping can save the front wheel or fork from unnecessary damage, and so is preferable to one that won't give.

The steerer is not CF....the fork is CF but not the steerer tube. Not sure how tight because it was my bike tech but I am pretty sure it was 13 Nm. I have checked it and it feels very tight and could cause damage to the stem if it is tightened anymore. I understand you don't want it so tight it cannot slip at all but it just feels like it slips too easy at this point. I may try some traction paste.

The problem may just be in the design of the Cinelli Alter stem itself, such that tightening the bolt(s) does not compress the stem against the steerer tube sufficiently to make it a tight fit. Sometimes fancy designs are just wack.

Even though the steerer isn't CF, stick with friction based over grit based paste. Grit compound will make circular scores as the stem is twisted into position.

A thin shim might also do the trick, though it could be tough to get in there.

Thanks for the help....I think between using traction paste, a shim and roughing up the steerer tube I will find something that makes it work.

Here is my new build if anyone is interested. https://i.imgur.com/7pG69KH.jpg

Nice.

Wow. That stem actually looks good on that bike. Well done.

Damn, dude, that is sexy.

That's an interesting design. Most stems are 5 nm, I can see why this would be higher.

Nice build. I have one on my Affinity, always liked they way they look on some bikes (even though mine is kind of a junker).

Flaccid.