Inisfallen

The seatpost on my Giant Halfway always slips down, no matter how hard I tighten the seatpost clamp. I can't tighten it any further because (a) I'll need a hammer to get it closed and (b) I'm afraid I'll break the bold, or the clamp itself.

I'm not a huge guy. I weigh about 190, which seems like it should be within the range the bike can support.

Any thoughts on how to solve this problem?

Thanks in advance.

rhenning

Post a picture when you get 10 posts. Guess is there might be a spacer missing or it is the wrong size seat post. Without picture who knows. Roger

79pmooney

This probably isn't the issue, but - look at the clamp with the pin in tight. Do the two sides of the clamp meet at the pin? You should always be able to slip a piece of cardboard between the clamp insides at the pin, (Of course, you can't, The pin is in the way. But with the clamp closed like that and if the pin were not there, could you slip that cardboard in?)

If the insides are hitting, all that pin is doing is trying to compress solid aluminum and the clamp is not getting any tighter around the seatpost. Good thing is that the fix is really easy. Take the clamp off (my web search suggests it is one of those easily removable ones) and simply file or sandpaper the inside faces until the clamp passes my cardboard test. (Any thin cardboard will do. Just no contact - ever.

If the clamp is not removable, get a thin file, and file or sandpaper and widen the slot, again until it passes the test.

Idiotically simple but you are far from the first to be so stumped (if indeed this is the issue). I've been there. Read the rest of the advice you have seen and will see here. Yo should not need a clamp death grip to keep the post from slipping..

Ben

linberl

I had that problem and the only thing that solved it was buying a qr clamp that also could be tightened with a hex key. I bought a Chromag clamp with a brass bushing. I tighten the qr normally and then give it one extra turn with a hex. Zero movement. It just means keeping a
little hex in my pocket when I ride so it's there if I want to fold it; I just loosen it slightly and then use the qr release.

Inisfallen

Thanks! A useful check. Unfortunately, that's not it. There's no contact. But there may have been some helpful information in your post. The clamp is indeed easily removable, and I took it off and put it back on, making sure it was seated right all the way around. Maybe that will help.

And thanks, rhenning, for your suggestion, but there's no spacer missing. There is a spacer, and there could not possibly be another. I'll post a pic when I can, but there's nothing missing.

Maybe linberl has the right idea. We'll see.

I hope there's a solution. I'd hate to find out that I'm just too big for a folder -- that's all I've got room for at home (typical NYC cramped apartment, with wife and three kids).

tds101 

I weigh 235lbs, I own multiple folders, and the issue usually is the seatpost clamp on most folders isn't strong enough. Try getting a fatter replacement clamp, or use the allen key type. Otherwise, I highly doubt you're too big to ride a folding bike,...especially a Giant branded model. Their folders are strong.

Juan el Boricua

Maybe spread a little assembly paste on the seat tube before insertion, as if it were a carbon fiber one?; it is the paste used on carbon fiber products to help in "gripping" without excess torquing that could crush the component.

Kabuto

Sometimes the slightest amount of oil can cause slippage. Try cleaning the seat post AND the inside of the seat post clamp (surfaces that clamp the seat post in place) with ethanol (or similar) to remove any oil that might be there.

I had a seat post slippage problem on a Tern Verge S8i that I was only able to solve after cleaning the seat post and the inside surfaces of the clamp several times with ethanol to remove a very slight amount of oil (probably skin oil from handling the seat post). Its been fine since I cleaned it.

Your weight shouldn't be a problem.

Fentuz

Clamp is one thing but a "forgotten" element is the shim. I use to get this issue with the jetstream, I change the shim because the old one had signs of wear (aluminium deposition, galling marks etc...) which were creating a point interference once clamps rather than line/surface. New shim for a ~£2 fixed that... even with a thin anodized seatpost.
I also went for a cane creek seatpost whish is made of an Ali bar/tube milled on the OD and retained small milled grooves providing grip. This does not move even on fast gravel rides...

Inisfallen

I was thinking of something along these lines. Screw Grab might work, same idea.

I will -- always try the easy stuff first, right?

I did check the shim, and that doesn't seem to be the issue. Although I guess it's impossible to tell for sure without a micrometer, which I don't have.

Thanks again, everyone.

rhenning

Is the shim slotted so it can compress or one piece so it will not compress? Roger

mirfi

Random crazy thoughts, sorry if any are repeats, been a long day.

If you bought it at REI have the mechanic there look at it.

Also as a diagnostic test, remove seat post. Tighten clamp on seat tube. Does it noticeably close any?

I think about thirty years ago I took a sharp chisel and scored the surface of a seat post a bit

Then I figured out where I wanted it to bind and whacked it there with a hammer. That worked.

Also is it possible to put another clamp that squeezes tight on the seat post itself.

Schwinnsta

I did this on my Brompton.

sweeks

I'm not familiar with the Giant seatpost clamp arrangement, but if it has a cylindrical shim between the seatpost and the seat tube, oil may be part of the solution.
I have 2 Dahons and a Tern that all have a shim. While it's true that oil between the shim and the seatpost will cause slippage, lubrication between the shim and the seat *tube* is helpful in developing enough compressive force to hold the seatpost in position. I use a very thin "smear" of wheelbearing grease on the outside of the shim. As the shim is inserted into the seat tube, some of this grease may ooze out; this must be wiped off so it doesn't get on the seatpost.
Another place where lubrication helps is on the cam of the seatpost clamp; this helps the clamp develop its maximum compression.
As noted, your weight is not an issue; I weigh 210 plus a heavy backpack, and have no slippage.

fietsbob

On my Brompton. also, .. which has a 1.25" seatpost (31.75mm) I altered a 31.8mm QR band clamp for frames, taking a lip off the inside edge,
and slide it down the seatpost itself..

to fold the bike I have 2 QR lever sitting on top of each other to open..

I'm 215 # FWIW..




...

Kabuto

I have 2 Terns and a Dahon. The Dahon has a shim, but neither of the Terns (S8i and X11) have a shim, so its interesting to read that your S11i does have a shim, sweeks. I would have thought Terns would all be the same in that regard.

sweeks

My Verge is about 7 years old, so it's likely some changes have been made. I don't see many Terns around my neck of the woods. When I was active on the Tern web site forum (and before that the Dahon forum), it was common to hear from new owners whose bikes had had their seatposts greased by the dealers they bought the bikes from. No wonder they slipped!

50PlusCycling

Take some coarse sandpaper, then wrap it around the seat post over the part which sits in the seat tube. Turn the seat post in circles while holding the sandpaper firmly. This will knurl the seat post somewhat, and give it more friction. You don't want to sand away metal, you want to roughen the surface. Wipe down the seat post with lacquer thinner, lighter fluid, or some other solvent, clean the inside of the seat tube as well. This was my usual fix for slipping seat posts when I was a bike mechanic.

fietsbob

real Knurling is actually done on a lathe, pressing the knurling tool into the surface rolling material up by pushing some down

Rolling is how spokes are threaded..




..

sweeks

I confirmed with my Tern contacts that the newer Terns do not have the shim. News to me! If the post and the inside of the seat tube are *verifiably* grease-free, nad you have the clamp adjusted so it's moderately hard to close, the seatpost should not slip. When my Tern was new, I had some slipping initially that went away after a couple weeks... I think the surfaces needed to wear in a bit. That was a shim-based system. You might consider wiping the post and the inside of the tube with acetone to degrease the interface. I would lubricate the cam on the seatpost with a good high-pressure grease, being careful not to get any on the seatpost-seat tube interface.

Kabuto

All good now. I experienced some slippage with my S8i when I purchased it used back in January 2018, but I sorted it out fairly quickly and its been fine ever since. I was a bit surprised by the lack of shim initially though.

Inisfallen

Great suggestion! So far, it seems to have done the trick. I rode maybe 25 miles today, and it didn't slip a millimeter.

Thanks!

bike.gang.uk

We have this aluminum seatpost for Brompton by KCNC, they also made some for Dahon before, not sure about Giant.