Seat clamp for Titanium Bike

[mnichols]

I'm away touring at the moment and I've stripped the thread on my seat post. I've managed to get enough purchase to continue but it needs replacing

Do I need a special clamp for a titanium bike (carbon seat post)? I think it's stripped as it seems to require more force to clamp titanium

Also, can anyone confirm the size for an Enigma Etape? It's about 5 years old. I think it's 31.8 but be good if someone can confirm

I'm thinking of the Brandx with bolt jumbo

Thanks

[Keezx]

Seat post is most likely 31,8, so the clamp will be 34,9, any good brand will do the job, nothing specific...
A titanium frame can be slippery, so full torque and paste might be necessary.

[pq]

You're better of with a campag (or campag style) one where the cut in the clamp is angled. It puts less strain on the carbon post. There was a spate of failures of record seatposts (I had one break) and the new style clamp solved the problem.

[gregoryoftours]

No grease for a carbon post but yes carbon assembly paste. As a stop gap in place of carbon paste you could try toothpaste? Abrasive in a similar way maybe- but don't hold me responsible for the results! Also buy a longer bolt and nut at a hardware store if you can't get a replacement clamp straight away. What does your seatpost have written on it diameter wise? Then add on what you think the seat tube will add to that and it should be easy to come up with required seatpost clamp size, as it's prob one of the three- 28.6mm, 31.8mm, 34.9mm. 2011 model of your frame had 27.2 post, 31.8mm front mech band so almost certainly also 31.8 seat clamp.

[gregoryoftours]

If the walls of your seat tube are thin just make sure that the lip on the replacement clamp isn't thicker, causing clamping problems and damaging your seatpost.

[Brucey]

several things can cause a seat binder bolt to be overtightened

- that the seat pin is undersized (does it wobble when the binder bolt is slack? If yes, it is probably undersized in most frames...**)
- that the mating surfaces are very smooth
- that there is grease present
- that there is no carbon grip paste present (although this itself can cause problems; it is not an infallible cure)
- that the frame is stiff (perhaps compounding the undersize issue)
- that the seat pin itself is flexible
- that the supported length inside the seat tube is too short

Often it is a combination of these things.

** Ti frames have a special issue; many of them have seat tubes that are internally sleeved near the top to accept a 'normal' seat pin whilst having a 'normal' seat tube OD. In both cases 'normal' can mean anything but is quite likely to mean 'Normal for aluminium frames' i.e. so that a standard collar can be used. Anyway this means that the seat pin is only supported over the (short) sleeve length within which means that issues concerning fit, friction and flexibility of the seat pin are invariably compounded.

Any potential for 'wobble' means that in service the seat pin tends to work its way downwards, regardless of how tight the binder bolt is. It isn't at all unusual for the binder bolt to be overtightened because "it clearly wasn't tight enough because the seat pin moved" etc

In the short run you may be able to install a (longer) through bolt and a nut (it will be M5 or M6 I expect) to secure the seat pin using the extant collar. Sometimes you can install the longer bolt the wrong way round and you may find that (say) an M6 bolt can be secured using a nut from a V brake block, which might even fit into the recess for the original caphead. This won't solve any underlying 'wobble' issue though (and I suspect you probably do have one). Therefore you may also consider fitting a shim of some kind (even a vertical 1" strip at the front, as long as the sleeve, might help) in order to improve the fit and reduce any wobble there might be. You can make a shim from beer can; it cuts easily using small scissors, eg the ones on a swiss army knife.

BTW any binder setup where a nut turns is better than one where the bolt turns, especially if the collar is a slack fit on the seat tube or obviously pinches more than the designer intended. The reason for this is that a turning bolt sees a cyclic bending load (tends to break the bolt, strip the thread etc) whereas a turning nut doesn't have such a nard time of it; the (stationary) stud bends once and that is it. You can often further improve the situation by seating the nut on a pair of curved washers as used on V brake blocks.

cheers

[mnichols]

Thanks, I think it's a combination of a stiff frame, and a cheap seat clamp. I also have a vague recollection of the bolt having stripped before and me replacing it with a bolt I had lying around which may not have been up to the job. This time it's the thread in the clamp that has been stripped rather than the bolt.

It's a fairly new seat post, the old one snapped last year. This one doesn't wobble but it takes a lot of force to clamp it. I've emailed Enigma for their recommendation but no response yet