This is driving me nuts. Thompson elite seatpost (aluminum, 31.8 x 300mm) keeps slipping down into the seat tube of my Litespeed Siena (titanium). The seat tube is butted internally, which means the internal diameter increases about 4-5 inches from the top; below that butt, there's no contact between the post and the inside of the tube. I've searched and searched for any reports of slipping seat posts in Litespeed Sienas or other internally-butted frames, and found no other reports of slippage or any discussion of butted seat tubes causing seatpost issues.

I've tried using ordinary grease, titanium-specific anti-sieze compound, and carbon paste. None of them make a difference. I've tried 2 different seat post collars and I've varied the torque on the collar bolt. No matter what I do, it's the same: the post slips about 1 mm over 10-20 miles. It's exactly the same in hot and cold weather - differential heat expansion of aluminum and titanium doesn't seem to have any effect. I've used this same seatpost in a titanium frame before with no problems.

Any suggestions? Thanks in advance.

How long is the binder slot? Have you tried another post? Andy.

Is the gap on the collar or seat tube closing up when you torque it? If there is not a clear gap then you are tightening the clamp/tube against itself and not the post. Perhaps the post is slightly undersized and/or the tube undersized. A few quick measurements/observations may give a clue.

First all understand that all the clamping happens at the collar and nowhere else. You also need 3" or so or snug running contact below that to stabilize the post so it can't rock which would cause creaking. Anny additional contact beyond those 3" is meaningless, so put the issue of the bulge formed tube out of your mind.

So assuming the post fits, which I'll take at face valus, let's look at the clamp. Take a look at these two clamps. Focus your attention on the transition area between the ears and band. No.1 No.2

Notice how the first is really beefy there and the second isn't. With the second, if tightened hard, the ears will begin to bend, while with the first all of the force of the bolt goes to tension the band. So before you go farther, is your collar like the first or second. If not, buy a better, beefier collar.

Now to get the best clamping, you want to grease the collar so it can slide on the tube and clamp evenly. Then because you have a well designed collar, you can feel free to use some added torque on the bolt (throw away the torque wench and tighten this until you feel the bolt resistance ramp up). Assuming it's a stainless steel bolt, try to stay below 7ft#s.

Now look at the rest of the picture, you have a polished and anodized post which is fairly slippery, then you grease it well to make sure it's slippery, then you want to hold it tightly. Doesn't make sense does it? But you do need antisieze or grease, so here's a trick. The clamp only holds at the top so you can grease everywere but there.

Put a piece of tape around the post at the right height. Now use solvent to thoroughly wash all the grease from the post, leaving clean dry bare metal. Use a rag dampened with solvent to clean the inside of the tube down about 1/2" or so, leaving grease below that. If you want you can add more grease below with a brush being careful to keave the top 1/2" clean. Insert the post, turning it around to spread the grease as you feed it in to the desired depth, but do not go oo far and pull it back up. This will give you a dry area for best clamping and should solve the problem.

If not, start fresh the same way, but paint a 1/2" band below the tape mark with nmedium grit lapping compound, which will bite into the frame an post locking them together. Save this in case nothing else works, because it will mar the post, and can score the metal if you twist the post while it's tight.

I have the same issue-- completely different bike, but two different posts, three different clamps. Still slips about 1.5mm over 20 miles. So I went to what I would consider the nuclear option, a double-bolt clamp, like the kind used on unicycles. The clamp has two collars, one to grab the post, and one to grab the frame. No slipping, guaranteed. Not for the weight weenies, it's over twice the weight of the clamp it replaced. You could also try getting a clamp for a 27.2mm post (which is for a 31.8 frame) grind off the little ledge in the clamp (if there is one) and tighten that clamp onto your post above your primary seatpost clamp. The belt-and-suspenders technique.

+1,A 31.8mm seat post also allows using a second 31.8* mm seat tube binder collar directly around the seat post itself,

I've done this removing the lip edge [Emery cloth around a dowel), on my 2nd QR lever collar on my folding bike seat post.. You can of course use a Non QR Collar.

*1.25 in = 31.75 mm


BTW seat tubes, if butted are butted Once and that is thicker towards the Bottom . (not twice .. that is the double butting for the other 2 frame tubes for the welding joints..

Double clamping is a good Plan C, but it shouldn't come to that unless the OP is very heavy (250#s plus). A good color and good preparation shou;d solve the problem. If it doesn't then using 2 clamps may solve it, and then again maybe it won't.

Thank you everyone for the wide variety of tactics. I'll try each of them one-by-one in ramping-up order. FBinNY - the current clamp is pretty beefy all around and dsbrantjr, there's still space in the slot. But I'm willing to do double-clamps if that's what it takes for peace of mind and not having to readjust the post every night.

A shop mechanic suggested I use carbon paste, which I've tried. It hasn't stopped the slipping, though I suppose it's possible it's slowing it. It hasn't scored the metal, which is not surprising since the little plastic granules aren't as hard as metal. Has anyone else tried carbon paste on metal components?

I've used Carbon past with a Thompson in my 520. It worked but I have finally settled on this Small Parts | Parts and Accessories | Surly Bikes .

I have either the PRO Fixing Paste or Ritchey Liquid Torque on all of my prone-to-slipping/squeaking areas, but it didn't stop the sliding post, just slowed it down. I'd also like to note, the $15 double-clamp from Taiwan made the seatpost feel significantly more rigid-- and I mean immediately. Time will tell, but I think slippage is pretty much impossible.