Seat collar tending to migrate up the seat tube

Hi all,

Just finished building up a new frame last weekend. I went all out (for me) on this build so naturally I am getting a bit emotional about this.

Arrived home yesterday after 20km of commuting and noticed raw metal right below my seat collar. Upon closer inspection, it was clear that the collar had migrated up the seat tube (towards my saddle) and took all the paint with it in the process. Absolutely gutted. Two things strike me as odd about this:

1. Why did the collar migrate upward? I torque'd it to 5nM as per spec. After taking it off and trying to tidy up the failed paint, I can't even get it back on there anymore. As soon as I reach around 4nM torque it's already slid up a few mm on the seat tube. I don't think this is safe to ride without risking damage to the frame. Is it conceivable the issue is with the seat tube itself? I can imagine any taper in the tube underneath where the seat collar sits could "entice" it to move upward in use.

2. It seems to me that the paint failed particularly catastrophically. It looks as if it just cracked along the circumference of the seat tube and slid right off the tubing without putting up much of a fight. Sound weird?

My next steps are to get another seat collar (on order) and see if that one will stay put. I also now have to deal with trying to get the paint fixed up.

Any theories/input/comments/words of encouragement are welcome.

Although both the post and clamp are marked as 5nM it seems that tightening to that spec causes the collar to tend to slip up off the top of the seat tube. I've tightened it to 4nM and so far so good.

Anyone ever encounter this before?

Thats a strange one. Sounds like the inside bore of the seat collar could be sloped/tapered which means it'll work it's way up as your tighten. I really doubt the seat tube itself is tapered. Try getting your hands on a new collar, something good quality

Absolutely normal to lose paint at the collar though I'm sorry to say. When I was at Saffron we'd slip-braze a stainless steel ring to the top of the seat tube to be left unpainted which the seat collar could grab onto for this very reason....

What's the frame?

Could it be that you're using a seatpost which is too small?
If you were, it'd pinch the top of the seat tube making it taper in towards the top and popping the collar off

Thanks for the comments fellas.

For the record, the "bad" clamp is marked as 34mm, I have a Thomson to try in 34.9mm. Seat tube OD is 32.5mm.

@PhilDAS, Frame is a custom jobby from a local (well respected) builder. Tubeset is Spirit HSS, so the OD of the seat tube is non-standard (at 32.5mm). Seatpost measures correctly with my calipers: 27.18mm, spec'd ID of the seat tube is 27.2, seems correct with the calipers as well.

@jammy, I was worried the clamp is a bad one actually as it seems to sit askew on the seat tube before I apply torque, which I guess could create an uneven force allowing it to slip upwards. I just received a Thomson clamp (inspired by Reilly's HSS frames) and I'm going to give it a try after work.

Hopefully the builder will fix up the paint under warranty. Right now I am definitely not comfortable with the ragged paint edge below the collar, and the exposed steel. Absolute bummer since the build is brand spanking new.

I appreciate the input!

You can get a clamp for that. I guarantee it's happened because the clamp is over-tightening because it's too large.

Contact Paul at Rideworks, I'm sure he can machine you up one in his new design. There's also a company making them in the US but importing one is barely worth it

There's a KCNC option in 33mm which I will track down next. I'm in Canada actually.

Reilly uses the Thomson on their HSS frames so that's why I'm giving it a shot. Spose I can send it back to Amazon.

I'll report back with results.

Ah great. Try http://www.dkg-cnc.com/bicycle.html if you're stuck

Nice one! Thanks for the link. The KCNC one seems very hard to find in 33mm -- I'll give those guys a shot if the Thomson is a no-go. Cheers

Welp. The 34.9mm Thomson is far too large unfortunately. An extra bummer since it's tall enough to conceal all the paint damage, which brings me joy.

Even more frustrating is that the clamp that is on there is labeled "34", which I took to mean the diameter. Just now I threw it on the caliper and it comes up as 31.8mm. Welp x2. And I suppose this could be the problem.

Wondering now if I could get away with the 31.8mm Thomson?

Don't measure the clamp, measure the tube.

You want as close a fit as possible. I presume the seat tube has the alloy bonded internal shim to reduce the diam to a standard 27.2mm for the post? (I'm just trying to be sure that it is infact a HSS seat tube)

Thanks again @jammy for the thoughts on this.

I have measured the tube, yeah. I was just mentioning the size of the existing clamp to bring more info to the table (and to point out the mistake I made assuming it was a 34mm).

The seat tube OD measures about 32.1-32.2mm at the very top (no paint), and more like 33mm where it is painted. It does have the sleeve added for a 27.2mm post, yes. I have had no issues with the seat post (Deda Superzero) slipping, even with the clamp torqued to 4nM, and the fit of the post is excellent.

The existing clamp seems to fit fine (as in I can fit it on the tube without any fighting) although it is a flexy clamp to begin with. I have the 31.8mm Thomson coming to try - I can always return it to Amazon if it doesn't fit. Otherwise I will have to look for a 32-33mm option. I really want the Thomson to work since it conceals all the paint damage (vain I know...)

A flexy clamp is what you want, not an overbuilt, stiff one.

Just got in from a ride and the original clamp seems to stay put when torqued to 4nM instead of the indicated 5nM. 31.8mm Thomson should arrive on tuesday/wednesday. I'm hoping this is a case of shittyclampitis and that's it.

Got the 31.8mm Thomson today. I had to pry it open a touch, but it seemed to fit fine.

I trimmed back all the paint so that it wouldn't rest under the clamp, sanded the raw seat tube, light coating of grease, and installed the 31.8mm Thomson. Went on and torqued up to 3nM no problem. That said, the "defective" clamp seemed to be fine at 4nM for the past little while.

Haven't ridden with the Thomson yet, but I am pleased that the paint damage is concealed and the install went totally fine. We'll see how it goes after I get it on the road for a few miles.

light coating of grease

Between the clamp and the tube? That won't improve friction.

PS The Nm figure quoted on components is the maximum, not the recommended figure: if it works at a lower torque, then it's fine.

Between the clamp and the tube, yeah. The Thomson instructions state to do this-- but they are the only ones I've come across to suggest that. I thought I'd give it a try since now its bare metal underneath and I would hate for it to rust.

Few days commuting under the belt and all seems well. Damage is concealed, collar seems to stay put, post is not slipping.

Still no idea what went wrong in the first place. But at least things seem good now. Thanks for the input all.