• As James says, Thomsons do seem to have a rep for being undersized.

    I don’t think I’ve experienced it personally but I’ve only owned one or two Thomson posts and i for sure know a couple people who have had issues.

    The fact the post has worked in other frames doesn’t really prove it’s not undersized, those frames have just been a better match for the post within the acceptable range of ‘tolerance’ or the clamp has be more able to take up the slack.

    Some manufacturers tolerances are shockingly wide. If you get a post at the narrower end of the range and a frame at the wider then you’re in for some struggle to make it work.

    I would put money on a non Thomson post staying put.

  • Thanks for the pointers. Seatpost coming up at 27.17-19 with calipers. I’ve applied Morgan assembly paste and torqued to 5n but still a slight bit of slippage. I’ve just ordered some finish line assembly paste as it seems to get better reviews than the Morgan blue stuff. Hopefully that works!!

  • Has the seat tube bean reamed? If not it doesn’t take much more than a blob of paint to mean that the post has a poor fit, so when clamped the post isn’t evenly gripped all the way round.

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