Custom Seat Post for Belt Drive

Oh so close to having the belt drive bike built up and shipped out. I am waiting on a different length belt. I couldn’t find the length I had calculated for when designing the bike when it was time to order the components, thought I could make do with a slightly shorter one, just to find that only the original length would do. Otherwise I would have to  swap out the sprocket or cog, and when its all Phil Wood stuff and the sprocket cost $300 I would rather find the right belt. To my relief I was able to get one right from the source(shoulda gone there in the first place).

One of the things that makes this bike even more special is that I made a custom seat post for it. The customer had originally asked for an integrated seat tube/seat post where the saddle clamps directly onto the seat tube and doing away with the seat post altogher. I was concerned about adjustability and to some extent strength.  I have seen a few bikes that have somewhat of an external seat post, where the tube bolts to the outside of the seat tube. This provides a little more movement, gives the appearance of a tall seat mast, but still seemed to be questionable durability wise. I liked the idea of a seat mast, with minimal clutter, but wanted some adjustability. I didn’t have to scratch my head too many times till I figured I could design and then make a post that clamps internally by way of a wedge bolt much like that of a quill stem.

While doing a little “r and d”, it turns out my idea was not at all anything new. Campy used to make one a long time ago, I found a shop in Wisconsin called Yellow Jersey ( I believe Jonny from Jonny Cycles used to work there)that at some point converted existing posts to internally clamping ones, and it also turned out that a lot of the bmx companies make them for their bikes. As I had already dreamed up the design of the post, made custom bars and dropouts, sourcing one of these pre-made ones was clearly not an issue. Once I had the frame in paint I began working on the post.

As I typically build all of my bikes by hand I don’t have my own lathe or mill, and have pretty limited experience on them. Luckily my friend Chris Watson, co-owner of Arundel Bicycles  , allowed me full access of the machines at the Arundel Development Center and bounced off ideas and techniques with me. The design was relatively straightforward. I started off with a stainless steel tube, turned it down to the standard seat post size of 27.2 mm. I then made a plug for the top end of the post that was counter bored and mitered. I brazed the 2 pieces together, and then made a stainless wedge bolt for the bottom end. I cut a few notches in the bottom of the stainless tube so the post could expand courtesy of a Titanium bolt Chris gave. As I don’t TIG weld, I then had Chris TIG weld some what were originally stainless down tube shfter stops onto the top of the post. These stops would then hold the hardware used for the Thompson Seat Post plate that I will used for actually holding the saddle.

Here’s some pics:

I don’t want to put too many pics up of the actually bike till its totally done.Since the last post I have had loads of people asking about the custom dropouts and how the belt went on. I purposely didn’t show any pics of the drive side drop because I was having to get a little more work done on the stainless faces. I still need to polish them up a bit but here is a little teaser to keep you people satisfied for a few more days.

3 thoughts on “Custom Seat Post for Belt Drive

  1. Hey Jeremy, just wanted to say that you do some beautiful work. Everything about it shows good taste and class. Your one of my favorite builders even though we have been building about the same amount of time. Your work is good inspiration. I can’t make it to the Texas show this year and I know I’ll be missing out. Enjoy.


  2. Hi! I know this has been a long time but I’m currently looking for even a small hope. I recently became an owner of F.Moser AX which requires the expand seat post. I noticed a couple of places could be able to modify a seat post but I’m looking for a Zero set back one.
    I’m not sure whether you would check this reply or not, but if you could find this, I would kindly ask whether I could order the exact same type of Seatpost that you made. I will look forward to having your contact!



    1. Hi Minjoo, this seat post required using a lot of tools at a friend’s workshop, which I do not have access to anymore so I cannot help you out with this. I seem to recall there being an old Campagnolo expanding binder seat post, not sure if it was zero set back. Best of luck.

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