Affinity Cycles: Prototype Seatmast Clamp May 11, 2010

While I was in Affinity ( @affinitycycles ) yesterday, Jason showed me the newest prototype seatmast clamp for their forthcoming Kissena frameset. Because the bike has a seat tube that is cut-to-fit, he’s been looking for clever ways to address the possibility of multiple people riding the same frameset at some point in time. Here’s one option that he’s developed.

Check out some more photos and further explanations below.

Since it’s a prototype, he’ll be making some minor tweaks to the design. Keep in mind, this is a plastic version; the final will be made out of aluminum.

Overall, I think it works pretty well. I recommended an interior, expanding quill-inspired design. What do you think?

  • i have a 09 FJP that uses this design and i can say that i HATE it. Its scary enough cutting your frame, and mine always seems to creak and come loose. Hopefully affinity’s is better quality!

  • DM


    A heavy, fugly solution to a problem that needn’t exist.

    What’s wrong with a normal, adjustable seatpost? Really – It has no benefits that I can see: Aero, weight, stiffness…? We are not Chris Hoy.

    The use of a quill/ wedge system would depend on the tubing wall thickness. Fork steerers are pretty thick; seat-tubes not so much.

  • luke mitty

    maybe he should make a bolt threw design instead of a clamp fit, having one side tapped. this would be much smoother and you could still allow for adjustability with multiple threw holes located up the seat post.

    either way its a great idea, i have always disliked the tear drop seat tubes with round seat posts.

  • The ’10 BMC’s have an interior expanding quill type design.
    Affinity version looks pretty cool. Should yield enough adjustment.

  • it looks like it is going to be very difficult to machine (and possibly very heavy). an alternative to a quill, as john suggested would be a lightweight composite filler in the seat tube, to stop the aero tubing from crushing during clamping. providing an unpainted surface for the clamp to dig into would also be wise, that paint isn’t going to look good after a few adjustments. looks neat though.

  • The Kissena will be offered with both the wedge and integrated clamp. I’m a fan of both designs, the problem I have with the integrated is adjust ability, also if you ever sell the frame… what happens to the next owner.? My solution is having the wedge bolt clamp for 27.2 post. Also the integrated clamp will come with shims installed which you can take out (2 1/8th inch shims) and two which you can install. This way you have room for adjustment. Take a look at the website to see how the current set up is.

  • It no that heavy at all. If you consider you loose the seat post, the weight is probably the same.
    The tube wont crush as long as you dont over tighten, we’re also playing with putting some teflon tape on the inside to help with paint rubbing.

  • Where do i get one of this guys?