Spotlight on the seatpost and saddle


(Mis)using the saddle adaptor pin

Robert Payne, Nov 1999:
The Brompton owner manual says not to put the seat adapter on pointing to the rear of the bike. Has anyone tried this anyway? Any damage to the bike?

Keeping it up

So now we have a seatpost extracted to the right heigth, how do we keep it there? Depending on your weight, the weather and the way you open tincans, it has a tendency to gradually slide down the frame as you ride.

Is tightening the quick release seat clamp bad?

Getting it up or down

David Cox, Mar 1999:
The Brompton owners manual says never put lubricant on the seat pillar and I have found the pillar slides down gradually if you use WD 40 to clean it.
However, I have now twice been embarrassed to find that my Brompton would not unfold because the pillar has stuck. The problem relates I think to getting the bike a bit gritty on the canal towpath and then putting it away wet.
I struggled to raise the saddle the other day [...]. The natural temptation is to swivel the saddle to try to get it moving. The basic problem is that the plastic sleeve in the frame has moved so that its gap no longer meets the gap in the frame. I managed eventually to yank the pillar up and because it had to perform several more times that day I went straight to a motorcycle dealer and sprayed it with a lubricant !
I have now taken the pillar out (I had to use another pillar as a drift and a rubber hammer) cleaned everything up and moved the sleeve back into position. It seems to work OK but a Brompton that wont unfold is a very frustrating object.
I rang Neil Gascoigne at Gascoigne Bros in Olton to order a new plastic sleeve. He said that to fit this the whole bike had to go back to the factory for a new sleeve to be reamed and glued in. Apparently even dealers dont have the kit to do this.
[...] A precaution for Bromptons used in all weathers is to keep the pillar clean (but not lubricated) and perhaps dry it when folding the bike. Swivelling the pillar once is gets stuck aggravates the problem.

Crunchy sound while retracting the seatpost / stuck post

Removing rust spots from the seat post

Osbert Lancaster, Apr 98:
I've got some rust spots on the seat post. Probably caused by riding in pouring rain then folding the bike and not riding it for a few days - so the seat post didn't dry off properly.
How can I clean the seat post and get rid of the rust - and prevent further spots? The manual gives dire warnings about putting oil anywhere near the seat post.

The rubber bong: an invention to keep your seat post clean

A wish by Peter O'Reilly and a suggestion by Ka Lun Tam, led to this invention:

{Erwin de Vries, May 2000} Here's how I closed the underside of the seat tube from water and dirt getting in:
I took a conical rubber stopper, the top of which just fits into the seat tube, and inserted it into the seat tube. I then marked it and cut off most of the rubber protruding from the seat tube, and attached the top of the stopper to a short piece of cylindrical rod *, which just fits into the seatpost (diameter approx. 1mm smaller than the inside of the seatpost). A bit of elastic cord** is attached to the rod, and to the top of the seatpost. The elastic should be tight enough to keep the rubber stopper against the seatpost when this is lowered below the frame. When the saddle is raised, the elastic is stretched, and the rubber stopper is drawn against the underside of the seat tube, keeping dirt out. The bit of rod is rounded off at the top, so that when the saddle is lowered, the rod easily enters the seat tube. Because the stopper is only marginally wider than the seat tube, it doesn't get caught anywhere in the Brompton Triangle, and even passes the LSD without problems.
There are a few things to be borne in mind though, if you attach this thingy to your Brompton (I imagine this could also work for other folders):

*Actually, I sacrificed the top of my old broomstick, when I found how neatly it fit into the seatpost (ever heard of Chuck Yeager? ;-) . [Later...] And that's where I went wrong, so I'd like to warn you. I thoroughly washed the bike, causing the bit of wood to get wet and therefore EXPAND while the bike was folded. It got stuck in the seatpost, and I had quite an enjoyable time getting it out so I could unfold the bike again (of course this didn't happen at home where I have all my tools) I've now replaced the wood by a bit of PVC rod. That won't get stuck unless I blow hot steam down the seatpost I suppose ; )
I don't think the length is very critical; on my bike it's about 1 inch.
**I didn't use a spring, fearing it'd make clanging noises inside the seatpost when riding over bumpy terrain. Apart from getting stuck, the stopper works beautifully. No more scraping noises from the seatpost when (un-)folding the B.

Replacing the seat post's sleeve in the frame

Keeping it straight

Telescopic seatpost

Andrew Brooks:
What is this and how does it work? My image is of something like a radio aerial with a quick release at each junction - something a bit flimsy and swaying and a nuisance to put up and down.

Adjusting the seat post after unfolding

Rail saddles on a telescopic seatpost

Telescopic seatpost versus long seatpost

Can one shorten a Brompton seatpost?

There are three reasons to do this:
  1. The telescopic seatpost needlessly sticks out ± a centimeter at the top of the folded package, and scrapes the ground on the bottom.
  2. The flare at the bottom of the lower or only tube, which keeps it from being raised to high, also makes removing the tube - for even more compact folding or cleaning - difficult; it has to be guided through the bottom after the clamp or saddle on top has been removed.
  3. Taking off a tiny bit (±20g) of dead weight.
With a cheap small blade I sawed off a ring. I sawed a tooth and bent it outwards as a replacement for the flare. Just bending the tooth a bit it not enough: it gets bent back each time you raise the tube. I had to bent the tooth 90 degrees outwards and cut off most of it.
An unforseen fortunate effect of replacing the flare by a tooth was that it now allows the tube to be taken out easily from above. I just turn the tube to where the tooth fits in the gap in the frame's clamp (the gap allows for the quick release to tighten the clamp around the tube).

How to make your own telescopic seatpost!

Len Rubin, Nov 1999:
Seatpost diameter is 1-1/8" (or 31.8mm) Custfold:
I obtained some thick walled s's tube, exactly right for the post diameter, and with a large steel 'cannonball' bearing ball and 7lb hammer, [later he wrote: a 4" ball and 14lb whack] belled the end out to match the Brompton original. This tube was cut to fit just above the frame when the bike is folded, and a cannondale MTB clamp used to hold the USE shimmed seatpost for the top 12" extension.

{Custfold, Aug 1997} [Second stage is a standard 1" seat tube] - the first version of the extending seatpost - my concept to accommodate a 6'6" rider with 38" i/l (I ride a 29" frame on a standard bike, with bars and seatpost well out), I found that the USE seatpost system offered a 1" seatpost with shims up to 1.25" at least.
My reason for the seatpost was 3-fold (sorry)
1) With the Mk 1 extension (a cut down seatpost, with a q/r clamp from the Bickerton on the top section of a Brompton seatpost) the leverage bent the top back & forward until it snapped off,
2) The weight & leverage on the standard tube size bent the seatpost, where it enters the frame, and made the post stick.
3) The saddle adjustment (normal grip plates) could not be kept tight, or adjusted finely enough.
USE are 2-bolt micro-adjust posts, up to 18" long, and some versions even have internal suspension. I got a sample length of 31mm (1.25") stainless tube, with generous wall thickness, and a USE shim fitted perfectly, as well as the tube fitting the Brompton perfectly. To use a seatpost larger than 1" does not give enough 'meat' for the clamp/shim in this style, so I expect that Brompton found a similar problem, and fittings are available for 1" seatposts.
Caveat with USE. The adjustment for Brompton 'frame' angles is on the limit, and if the seat starts to creak beware. One of the bolts will soon fail through fretting fatigue - catastrophically (ouch), and you have to ride home with no saddle, or do him big buggerup repair job
PS a USE rig is expensive (in the UK) c.UKP40 for the post & shims and a cheap clamp. Specialised 1.25" clamp c.UKP20.

Alternative seatposts

Ultralight Titanium seatposts

See also Len's Ultimate Folding Bike project (Genetically Modified Bromptons - Leonard Rubin's UFB ("Ultimate Folding Bike" or "Super-Brompton") project). Leonard Rubin:
The seatpost has an integral, very robust, quick-action, micro-adjust head, permitting very fast saddle removal, while retaining angle adjustment, for airline overhead baggage stowage! It is available in any length (within reason, of course, for practical and safety considerations), and two wall thicknesses. The strength-to-weight ratio of Titanium is phenomenal, and it will never rust, corrode or become horribly scratched, as with other post materials.
The weight savings over the original Brompton steel posts range from 125g to well over 250g! Combined with the saddle upgrade, this can easily save a pound! Also a much greater range of fore-aft adjustment is possible, and in most cases, that heavy, scary extender gizmo is no longer needed (saving even greater weight savings.)
As an added benefit, titanium is naturally springy, resulting in a more comfortable ride! The prices range from $100 to $115, depending on length and wall thickness. Your inseam and weight will determine exact specifications. I can make these for Moulton owners (and others) as well.

Carbon fibre seat post

Comfy saddles

Alasdair Baxter, May 1999:
Being somewhat heavy, I find that the original saddle becomes quite painful on the nether regions after a few miles. This is doubtless due to the concentration of my great weight on a relatively small area of my body.