Hi ever since I had a folding bike (mine have always been Dahons) I have had - on and off - the problem that the seatpost decided to slip into the tube/frame. On one occasion I wrecked the post clamp by overtightening, so clearly got that one wrong .
Does anyone have any suggestions (ideally based on their own experience) of how I can deal with this "phenomenon"?
malverncyclist wrote:Trouble of course is that this solution would partly defeat the idea of a folder ... ?!
Yes, sorry, I realised about half a second after hitting Submit that probably wouldn't be helpful. How bad is the slippage? A couple of millimetres during a ride or something much more drastic?
Could a quick release seat tube clamp, the type designed for frames, only in a smaller size to fit the seat post, be nade to work? Then you could have a quick release option allowing the seat to operate.
Obviously not a long term fix but would stop it slipping in the short term.
Hi Martin, how about a piece of old bike frame, cut to the right height/length, and used as a large spacer over the stem?! Shouldn't slip down then, should it?? Pop it in your Carradice saddle bag when you fold the bike up at work. All the best, Rich.
I've never had this problem with a folder and IME it's only happened when the seat clamp couldn't be tightened enough: in fact, I can't see any other reason it could happen if it's been tightened so much it causes damage. The only time I remember it happening to me, I used a different type of nut and bolt. (The original nut was blind so the bolt could only go in so far, so I sorted out one with the hole open all the way through.) The only other way I can imagine something like this happening would be if the gap in the seat cluster closed completely before enough clamping prfessure had been applied. I suspect that would be more likely with a slightly under-sized seatpin and if fitting a bigger one wasn't practical, widening the gap in the frame slightly by filing should work. On a new bike, it must be one for the retailer to sort out.
Had this on a steel mountain bike with an aluminium seatpost. After trying this that and the other what worked for me was cleaning off the seatpost then dusting it with tailor's chalk (climber's chalk works too apparently, but not the sticks of chalk you use when drawing on pavements).
It happened on my first Brompton. Overtightening can damage it. There's good advice in their service manuals as I recall. Had to clean the seat post and make sure there wasn't any grease on it and also the plastic sleeve. This usually works eventually I had the plastic sleeve replaced by a Brompton specialist.
My Dahon did suffer from slipping seat pin syndrome when I first got it (I'm quite big and heavy) - cleaning the seat pin and the interior of the tube with degreaser and then meths (yes really) did the trick (piece of rag stuffed in the tube with stick to push it back and forth)
I now have a Dahon "track pump seat pin" which has been fine ... the Vernier says that it's a just a gnat's bigger in diameter than the original seat pin, perhaps that makes a difference?
I've had this problem with two bikes though neither was a folder.
With one I added an extra seat clamp which cured the problem. It was a Woodman clamp which didn't have a step or ridge on the inside, most do. You should be able to find a clamp which is both quick release and smooth inside.
With the other bike I used carbon assembly paste which worked. The label has come off my small white tub/red screw top but I notice that Tacx and Finish Line are selling similar products. It's a black paste which increases the friction but might not be a good idea if there's a risk of getting it on your clothes. It's OK for a normal road bike where you aren't constantly removing the seatpost.
Edit: Looks like I've got FSA carbon fibre assembly paste, just seen some for sale on eBay.
I have finally fixed my Brompton's slipping seat post. (100Kg rider.) I tried the cleaning and tightening fixes but they still did not fix it. As was said in other posts, it is dangerous to overtighten the Brompton's seat post clamp, since it can do damage. Frankly, I think that Brompton is responsible for all this, and should have chosen a more basic and rugged clamp for the bikes.
To make the fix rock solid for all practical body weights, an additional quick-release seat post clamp should be slid onto the seat post where it emerges from the frame. The extra clamp shares the load with the existing Brompton clamp and avoids the problem. This allows normal use of the existing clamp and does not impede bike folding or modify the bike.
Sadly, finding an exact fit for the quick release seat clamp is not straightforward. It is found that the best size is to buy is a 31.9mm clamp size, then apply a slight modification to it. Such clamps have an inside proud rim of about one millimeter on one edge, (probably not noticed by most), that must be removed by filing for a neat fit. It sounds a bit extreme but when done, the results are perfect. A vise is needed really to hold the clamp and a suitable round file.
I hope that this is of use to some, Best Regards to All, GlueGunny
robgul wrote: I now have a Dahon "track pump seat pin" which has been fine ... the Vernier says that it's a just a gnat's bigger in diameter than the original seat pin, perhaps that makes a difference?
yup the bigger the better.
I note with interest that the conventional brompton seat pin is 31.6mm, and yet aftermarket seat pins often come in 31.8mm. I would say that the latter is far less likely to wobble and therefore ratchet its way downwards (which is the usual mechanism of the slippage)
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