seatpost clamp for funny sized frame

Hi all,

my new frame for my schlumpf (made by, not schlumpf) has finally arrived. However, it came with a wussy clamp, designed for a 31.8mm seat tube, which snapped and made me walk a couple of miles this morning. I swear I’ve spent more time walking with the schlumpf than I have riding it, that’ll teach me to buy first generation products where you’re paying to do their testing.

The seat tube appears to be 33.4mm outer diameter. Which isn’t a size seat clamps come in.

If I’m trying to bodge it with a wrong sized clamp, should I use a bigger one (designed for 34.9mm), or a smaller one (designed for 31.8mm).


Hey Joe –

Sometimes you can use a slightly larger one. What you do is take out the pin/bolt thing, then cut out part of the clamp so that the gap is larger, then reassemble it. If it works, the clamp will then be able to close more and do the trick.

Good luck!

You could also use a slightly larger one and make a shim with a pop can or some aluminum sheeting.

Shim-shimminy shim-shimminy shim-shim-shiree…


Having spent yesterday trying various bodges / shims etc., we’ve decided that the solution is to machine the (extra super duper thick) seat tube down by .7mm, which will make it into a lovely right sized seat tube. Given the ID is 27.2, there should be enough spare metal left over.


Wow, that really is thick!

Re: seatpost clamp for funny sized frame

On Thu, 27 Apr 2006 07:27:58 -0500, andrew_carter wrote:

>Wow, that really is thick!

You realise that 6.2 mm is TWICE the wall thickness, right?

Give me a little credit Klaas. :slight_smile:

Forgive me if I’ve misunderstood the problem and the terminology, but:

By ‘seat tube’, do you mean the part of the frame into which the seat post goes? That being the case, and assuming it’s integral with the rest of the frame, you’ve got the facilities available for somehow mounting a uni frame in a lathe (or conceivably a milling machine) to turn off some of the diameter of the tube?

If so, wouldn’t it be a lot easier to turn a bit of billet aluminium to make a beefier clamp of the right size? This is so obvious that I’m sure the answer will be more for my benefit than yours…


Please understand that the crown has been produced by a quick sketch primarily to solve my problem with my Coker Schlumpf. It was not meant for sale or anyone else. So wall thicknesses etc. were not specified.

The seatpost section of the frame is removable so it will be easy to machine down in the lathe.


Like Roger says, the frame comes apart, so it’s just a matter of doing some engineer magic to the tube. I don’t have the facilities for doing anything, so it makes most sense for (thanks Roger!) to make it the right size so I can fit a standard clamp on, and also I’d guess it’s much more simple to do something to a tube than to machine a whole clamp. Like Roger says, the new frame was a one off he did for himself and was nice enough to let me have when my original frame snapped, so it’s not surprising that there’s a little niggle or two to be fixed.