carbon seatpost torquing question

[paczki]

My beautiful Bob Brown bike takes a 30.8 seatpost. Bob has it set up with a 27.2 Reynolds seatpost and a shim.

Twice now when riding the trainer, the seatpost has slid. I've tried using carbon compound between the shim and the seatpost, and I've torqued it up to 6. I'm very nervous about crushing carbon seatposts.

I weigh about 190, and the first time it happened was when I was sprinting on the trainer. The most recent time, just riding.

How high can I torque it? Thanks!

[toaster]

Park Tools website has a guide to torque specifications for bicycle components.

[Dave]

If the shim has a split in it (just about has to) Align it 90 degrees to the split in the seat tube. A well made post should not be crushed. I've put scrap pieces in a vise to see what it took to crack a tube and it was amazing how egg shaped the tube had to be before it cracked.

I'd go on up to 7Nm. If that causes problem, than I'd say the post was poorly made.

[LO^OK]

My beautiful Bob Brown bike takes a 30.8 seatpost. Bob has it set up with a 27.2 Reynolds seatpost and a shim.

Twice now when riding the trainer, the seatpost has slid. I've tried using carbon compound between the shim and the seatpost, and I've torqued it up to 6. I'm very nervous about crushing carbon seatposts.

I weigh about 190, and the first time it happened was when I was sprinting on the trainer. The most recent time, just riding.

How high can I torque it? Thanks!

I think best is to check with the manufacturer. I have a Look Ergopost 2 and the specifications are quite conservative: "torque tension 2 m.daN."

[paczki]

Thanks, I can't find the specifications!

Bob suggested I use a bit of blue locktite to hold the shim in place. That seems like a good idea, since the shim is the problem.

[LO^OK]

Thanks, I can't find the specifications!

Bob suggested I use a bit of blue locktite to hold the shim in place. That seems like a good idea, since the shim is the problem.


In a similar circumstances of slipping post (bought a new frame once used for display where the dealer foolishly trimmed inside of the seatpost clamp, I suppose, because scratched the seatpost) I used epoxy for metal applied, a la nail polish, with a small synthetic brush. This way I could get an all around uniform thin layer.