Mechanics and Fixing Any Questions Answered

Measure the Thomson. My experience is they can be under sized and prone to slipping.

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Annoyingly I leant my calipers to a friend and she’s kept them

Can you try with another seatpost?

I’ve ridden it in a number of other 27.2 sized frames no problem

My other one is in a carbon frame and covered in carbon paste and a bit of a hassle to mess around with. Might try taking the Serotta to 6n :-|

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.
I had forgotten that trick.
Rear mech shifter goes green.
No reaction from the left shifter (front mech). Is it dead? Bad contact somewhere?
The weird thing is if I hold shift button down for 2-3 secs (either direction) the front mech sort of jolts. But no real change in position. Just a very small "flicker".
I'm hoping my lbs can look at it this week.

Cheers for the advice. I will give it a go.

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.

No it hasn’t to the best of my knowledge. This morning I swung by hubvelo en route out to Essex and they kindly let me stick some mucoff assembly paste on it for nothing but that didn’t work either. Maybe finish line will be better. Any advice on what is an appropriate torque to go to? I’m wary of anything above 6 and have read contrasting things on the net

As DJ and MV both say above, Thomson seatposts slip. I had the same problem years ago, but I think mine is so undersized it's actually a 26.8 marked incorrectly as a 27.2.

Two other people have complained about same issue here in recent months too:

https://www.lfgss.com/comments/15444354/
https://www.lfgss.com/comments/15886232/

Prob needs it's own thread.

Small sample size, but I have 4x Thomson posts in two different marked sizes, made 10 years apart, and they’re all bang-on...

I'm sure that will be the case most of the time, but there also seems to be a lot of people that do have issues.

Nightmare. So what's a decent alternative in the following flavour; inline, 27.2, black, alloy or carbon, less than £100? Pro Vibe Alloy? Bontrager Elite?

I’d measure your existing post first with decent callipers before chucking money at it...

I’d also not be averse to nipping the collar up a touch more.

For sure! I measured up with decent calipers and will try the finish line carbon paste to see if it makes a difference. Wondering if it's OK to torque beyond 6n?

Get it reamed. Has it been repainted at some point?

Yup

That’s likely your problem. Get it reamed. My wife has a fat bike. It was repainted by previous owner and the seat post kept slipping. Got it sorted by lbs and it never slipped again.

Is it possible it’s already been reamed, but a little too much?

Maybe but I’d suggest that lack of reaming is more likely the issue if it has been painted and not reamed.

OK, thanks for the suggestions all. It was repainted by Argos pretty recently and they did a very thorough job so would be surprised if they hadn't reamed it at the time - also looks very clean inside tube profile.

Derailleur capacity question. I've got a road link extender thingy I use on a bodgy 1x10 set-up at the moment.
I now want to add an Ultegra double chainset. Will the capacity of the 6700 ss rear derailleur be able to handle a 12-34 cassette with 50-34 on the front?
According to Shimano it's max capacity is 33t. I calculate the set-up being 38t. I know Shimano are often conservative on this stuff, but am I wasting my time before even giving it a whirl?