Steve M.

My ideal adjustment is at the very top of the normal post. It tends to sink over the course of my 20 minute commute under my clydesdale frame, no matter how tight I keep the clamp, creating the knees-at-my-ears sensation.

I'm wondering if the wobbling created by the post's long and imbalanced reach contributes. If I used the longer post, thereby grabbing post midway on that shaft, might that help?

Steve M.

Still Pedaling

Good question, but logically one would think that it shouldn't matter. I read somewhere that seat posts can vary in diameter -- maybe enough to create the issue you are talking about. Again, logically that shouldn't matter either. That's why we have the seat post lock. Is there someone who can check to make sure the locking device is working properly?

I hope its not because of the length as I'm going back to perhaps change out the longer post for the standard length. If my memory serves me correctly, I believe the test bike I rode had the standard post and it was fully extended during my ride. It fit me fine. Reason for changing it out is that the longer post will not allow the bike to fit the carrier bags, particularly the solid carrier without having to remove the seat.

fietsbob

Steve : I offer my solution , not theory, I bought a QR seat post band clamp .
the same size as the seat post itself.

then I took off the inside lip on what would be the band's fitting on the end of a frame's
seat tube , until I could just slide the band QR over the seat post ,
it now sits upside down on top of the frame 's QR..
to fold I just open both QR's ..

the one on the post itself slides up the post ,
then, when I pull up the post again , I slide QR No.2 down and clamp It there ..

If you are going to buy another seat post , consider the telescoping one ,
it will not stick up quite as far as the extended one , when folded
and if you are packing it you can always take out the upper section of the telescoping one.. with the saddle.

I got the rubber Bung for mine so the end of the post will not dig holes in the nice
(hardwood?) floor or grind/ chip off the end of the post if pushed into the pavement.


there are still the TI seat posts optionally ? are there ?

1nterceptor

I would go in steps with the easiest one first.

1. When you say the clamp is tight, you tightened the bolt?
2. Pull out the post and clean it and the sleeve/collar.

tourer78

Try a smear of carbon fibre assembly paste on you seat post ( I know its steel ) this works a charm on my bike fridays as I have experienced this problem in the past. Hope it helps. You should be able to obtain it from any bike shop, I ordered mine in small sachets online

bhkyte

+1 on trying basics first.

1) Roughen up post with sandpaper where you clamp?
2) Change the plastic piece inside frame that prevents seatpost being pulled out. They do wear out over time.
3) Have you got the brompton self locking frame clip as this has a longer QR than standard clamp ,unless I missed an upgrade.

2) would be my first port of call, also give the post and frame a really good degreasing and drying.

chagzuki

It strikes me as fairly ridiculous that this problem persists on expensive folding bikes. I switched out the stock seat post for an alloy one that I picked up from a cheapo folder. The anodizing is wearing a little so I don't know how long it'll last me, but it's never slipped whereas the original steel always did.
However, I wonder if there's some sort of durable, thin cloth tape, or textured tape that one could rap around the area of the post that is clamped, something with enough texture to prevent slippage? I've just seen some bathroom anti-slip stuff on ebay but it's probably too thick.

fietsbob

Things are different with 140 pounders on the saddle than 190 pound riders.


my Bike Friday got one of Mike Ahrens' 'Wise Crackers' directly on the seatpost. 27.2,

above the regular seat post clamp .. non QR , but, a similar function, + an additional one..

Steve M.

These are all good. The clamp is stock, and the bolt is tight enough that I worry about tightening it up further. I like the carbon paste idea. I think a bit of grit on there would do the trick.

smallwheeler

you dont want "grit" in there at all.
start with the basics first. just use standard bike grease on the seat tube. seems counter-intuitive but, it will actually help hold the tube in place when clamped. after trying that, if it still isn't working, you can try the carbon paste. an important note here is that you should periodically clean the old grease off and reapply with a thin, fresh coating of grease. grease attracts and collects dust, dirt, and grit which you don't want in the tube. if this doesn't work, i think fietsbob's suggestion of adding a seatpost clamp of 31.8mm ID to to the post itself is a good suggestion (that will definitely work).

bhkyte

Can not see how adding grease will hellp with what is a friction issue.

Evillv stopped this problem on his merc by drying the tube , I stopped mine on my merc by cleaning with alchol and roughing area, and added the brommie self locking clip.
On my preivous bromie I replaced the plastic trim and roughen the seat post. (Only in the top area where it was clamped).

I had problems recently getting a dahon andros stem to hold bullbars on my brommie. Sloved this by switching from chrome to anodised metal.

I have noticed how prone to rust my new brommie seatposts is also.

fietsbob

Carbon Paste is Grease with sand in it, you should never add grease to your Brompton seat post .

just add the grit if you want,
rough up the chrome where you want the seat post plastic shim to grip better.

a few strokes with steel wool around it at that specific spot .

on my Mk2 I replaced the plastic shim .. used Hot melt glue ,

then played the heat gun on the frame, there till the metal
was warm enough to let the seat post squeeze out the glue enough to get the post In.

smallwheeler

brompton seatpost is chrome plated cromo steel. you do not want to scratch or otherwise abrade the seatpost surface in any way; that will not help seatpost slippage. a thin layer of fresh grease creates a sealing effect between the tight tolerance of seatpost to frame tube.

also, the application of a thin coating of grease has the added benefit of preventing rust from forming.

if you have rust forming on any part of your bike, frankly, it means you are not taking care of it properly.

smallwheeler

fiets... in most cases you are rightest of the righteous, but in the case, you are.. ahem, the wrongest.

fietsbob

see what the manufacturer in England says.. I go and did, say with their advise
clean off Any Grease or oil . dry fit is their recommendation ..

and grease is the LAST thing they will suggest . last as in Never.


You can to with your carbon fiber wonder bike what you want .


Dueling opinions .. in fact I really dont care, in general , go play in the Traffic

I got the hell out of NY when the Navy let me Leave ..

bhkyte

My ridgid bike feature well greased seatpost.

On a folder I know not to grease.
All the manuals for my folders state do not grease the seat post.
Rust has not a problem on my other old folding bike seatposts, funny that. So when it appears on the brommie seatpost I treat it. Its disappointing for a 6 month old part that's not had much use and been well looked after.

You may grease your seat post but the manufactors don't recomend it.

smallwheeler

i do, in fact, "play in the traffic" come rain or shine on a pretty much daily basis. i also clean and lube my brompton routinely (including the seatpost). in four years of daily riding in conditions that include snow, sleet, road salt, and hurricane flood water, i've never seen so much as a spec of rust or encountered any seatpost slippage. opinion based on personal experience. YMMV.

bhkyte

Good luck curing a slippling seatpost by greasing it!

I would be interested to see if anyone sloved a slipping seatpost on a floder this way.

I await the flood of replies. Keep the flood away from my rusting bikes lol
Anyway peace brother.

smallwheeler

peace be upon you also, brother.

fietsbob, although he suggests i "play in traffic" which implies he would be happy if i got run over by a bus, still had the best idea in this thread for solving the OP's problem:

add a 31.8mm quick release onto the seatpost.

bhkyte

If you did get run over by a bus it might oval the seat post tube. This might stop the post rotating so that your seat is always centred.
Every cloud has........

Remember all bikes are folding; given enough force .............

Folding bikes are different in that they are designed to unfold.

dynaryder

Nope,they went to aluminum a couple years ago. Tried to order one,dealer put in the order,Brompton kept deferring it,finally after a year I canceled the order. There is a seller on eBay that does a ti post for $150,been thinking about getting one of those. And unlike Brompton,they have it marked on the side.

dynaryder

Steve:might want to try roughing the inside of the seatpost clamp. Another possibility would be to have the post powder coated in a rough finish.

fietsbob

the .3mm of diameter added by the typical powder coat job would certainly make it fit tighter.

smallwheeler

yeah, steve. a couple of great ideas on how to ruin your bike. proceed with caution.

just add a quick release clamp to the seatpost and call it a day. it will work.

bikebikebike

Necromancing this thread, but my post is not sliding well.
Cleaned it , and was wondering about lube, so did a search.
Typical internet foe-rum cacophony.
Brompton sez "No".
Mob says everything, short of drilling for a set screw.
Abrasion for slipping has issues, as do various grits

Would a lube not harm the plastic bushes (AKA liner,sleeve) the seatpost rides in?
Lube seems fine in metal-metal, and carbon, but plastic bushings used in the B are not common and not easy to renew.
The sleeves are not a 'ready to fit' item. They have to be reamed with the Brompton reaming tool and held in place with rubberized superglue.
Though workarounds are applied in the field.