fietsbob

My Mk 2 Brompton, bought used, had a chronic slipping seat post,
lost a half inch or so in a short days trips, new plastic bushing didn't help.

so I went down to the Local Bike shop and got another seat tube Quick Release band
for a 31.8mm seat-tube , they have a Lip edge to keep them on top
That Lip inside, locates on top of bike's frame tube, normally,

Filed that down so the whole thing is 31.8 ID , flipped it over
so now there are 2 Quick releases stacked on top of each other

And the metal on metal grip is, it seems, holding well ..

PDR

I’ve never had any problem with the titanium seat post on my lightweight S-type Brompton ..
And there are 3 other Brompton within the family with standard steel seat posts, again no slippage.

fietsbob

Thats why I was specific, Used and a Mk 2.. You have a later version, Mk3 is featuring Sachs hub for the 3 by 2 6 speed model

You have a brand new Mk4 if you have a Ti seatpost/ fork/and rear end.

If I had another loose $2grand I'd be tempted to get the new Ti parts one too

edwong3

It seems that I've always had an issue with seat post slippage if they were chrome steel. Aluminum seat posts have never had that problem.

fietsbob

Helpful to not be polished, some tool marks left as the lead screw moves
the lathe cutting tool along the length of the tube as it makes the outside diameter uniform..