27.1mm seatpost

Hello people, I need to find a nice shiny seatpost for my late 70s Merlin. Been told I need 27.1mm (bike shop measured) but can't find anything good new or coming up on the bay (one month looking). How low can I go with the size considering shimming or just tightening really hard, can I go to 27.2mm and pray for some allowance?

can I go to 27.2mm and pray for some allowance?

No !

Go for 27.0mm, you may not even need to shim.

27.0 will do with no shim

not even 27.2mm with an inverse/negative shim?

Thanks guys, have ordered 27

inveerse!!

Thanks guys, have ordered 27

That's you covered for a few years then.

oh very good..........

thought id stick another query in here rather than posting more basic question thread.

I measured up the internal diameter of my seatube with a vernier, which is 26.9mm.

I thought that'd meant a 27.0 would be ok (silly me, it wasnt) but like some reasurance of what the "correct" size should be? would 26.8 be too snug, or just perfect?

try it out is the best way to know. good chance your lbs will have an old 26.8 hanging around in the back you can slip in there.