Folding Bikes - Seat Post Slippage

Thanks to advice from you all, notably Jur, my initial problem with my seat post slipping is greatly improved. However, in a longer ride, say more than an hour, or when the road has been particularly rough, it still slides down a bit. A friend has offered to drill a hole in the post at my preferred riding height, so that I can put a pin in the post to keep it at that position. The pin could be easily removed to slide the post down when folding.

Would this weaken the post, compromising the bike's safety? Any other down side that you can think of?

Thanks to advice from you all, notably Jur, my initial problem with my seat post slipping is greatly improved. However, in a longer ride, say more than an hour, or when the road has been particularly rough, it still slides down a bit. A friend has offered to drill a hole in the post at my preferred riding height, so that I can put a pin in the post to keep it at that position. The pin could be easily removed to slide the post down when folding.

Would this weaken the post, compromising the bike's safety? Any other down side that you can think of?

It would certainly weaken the post depending on the size of the holes.. have you considered a second q/r clamp that just rides the seatpost?

Have greased the contact area between shim and frame (assuming there's a shim)?

From day one we had seatpost slippage on our two Bromptons,
made-up a secondary clamp for each bike and this solved the problem.

Regards

Neil

I never tried this, but maybe ...
http://www.sjscycles.co.uk/sessionID/DPN/currency/EUR/product-Brompton-Brompton-Rubberised-Glue-for-Seatpost-Sleeve--QGLUESS-13546.htm

The seatpost of my Brompton used to slip a little bit. By tighten (carefully) the clamp the problem was solved.

21 pounds sounds like a lot for a little bottle of glue? But I suppose it's worth it if it gives you peace of mind.

Have you considered a second q/r clamp that just rides the seatpost?
No, but it sounds like a good idea. I'll check with my favorite LBS and see if they have one.

Have greased the contact area between shim and frame (assuming there's a shim)?
Someone had suggested this in an earlier thread, but the way they put it, it sounded like they meant to grease the seatpost, which would probably make it worse. But the way you put it makes some sense. I think this is worth a try.

The glue sounds a bit messy, and might make it hard to slide the seatpost when I fold the bike. I think I'll give it a miss.

I've said the same thing in other threads and no-one has taken any notice but it worked for me on my Dahon and is entirely logical. Free movement of the shim allows the clamping force to be distributed evenly around the seat post. The only problem I had with this was when I over-greased it and the shim sometimes slipped as I moved the seat post.

Definately what chagzuki said!Worked on my Dahon,and makes sense.Just a light film on shim.Made all the difference.

..Free movement of the shim allows the clamping force to be distributed evenly around the seat post.

This is a good point. Currently I Liquid Torque both sides of the shim but next time I will try to Liquid Torque the inner surface of the shim and grease the outer surface. My Thudbuser shim has a lip at the top so it cannot slip down.

Kam

On the Brompton forum (Yahoo) there is (was) a discussion abut the slipping seatpost
found this

Manual page 18, 5-8 NM.


Seat clamp:
The quick release clamp (QR, fig FS1) should be kept adjusted so that the lever closes firmly when doing the clamp up; if the movement is slack and easy, with little resistance, the seat pillar will not be properly secured. As a guide, with the seat clamp lever forward (i.e. done up), the adjustor nut AN should be tightened with a torque in the range 5-8NM and the maximum closing force needed at the end of the lever while securing the clamp should lie in the range 80-120N. The correct setting will depend on the weight and strength of the user.
Do not over-tighten, as this can cause damage. For normal adjustment during the life of the machine, a sixth of a turn or less of the adjustor nut will normally be quite sufficient.
If, after adjusting the clamp, the seat pillar slips in use, then the cause is almost certainly oil or grease on the pillar. Remove the seat pillar from the bike, and using soapy water, thoroughly clean both the seat pillar and the sleeve in the main frame.


maybe it's of any help
Jos

What I had already done was thoroughly clean the seatpost and the inside of the post hole with alcohol, not soap and water. I also lubricated the Q/R mechanism. This does help considerably, because I only have to readjust the seat about once an hour, rather than every 15-20 minutes as I did before I did this. I also was tightening the Q/R too much, and it DOES damage the Q/R - stripped the screw - I had to buy a new lever and screw.

Haven't tried the suggestions here yet, but I will - probably try lubricating the shim this weekend.