Originally Posted by
kendall
For the sleeve, instead of wrapping a thin shim around the seat post, try to find a short length of tubing or conduit that is a pretty close fit on the tube, then cut a lazy spiral around it, maybe 1/2 turn in the length. Often a shim will leave bends in the metal that will keep closing up and need constant snugging.
(EDIT: with the spiral cut into it, the clamps can easily close the cut you made allow even clamping pressure)
A set of 'pretty' seat clamps for a larger post should work and look decently.
I'm wondering if you'll be happy with that design, the way the seat post is angled, it's going to change the way the trailer follows in turns. It may try to lift the rear tire on the bike when turning.
Not sure of the angle on your bike so it may be a liveable effect.
Ken.
I thought that a thicker shim might make a difference but I only had the aluminum can available at the time. The seatpost is 26.8mm in dia, and the 1 1/8" headset is 28.575mm (say 28.5mm), requiring a shim with .85mm wall thickness. I was considering either buying an appropriately sized bit of tubing from a metal supplier and having the local bike shop thread it (the co-op only has 1" dyes), or cutting a 1 1/8" steer tube and either boring or lathing out the center. I'd have to make friends with someone who has a nice machine shop, and I dont think the steer tube walls are thick enough to handle the requisite machining. I could use a threadless headset if I could get ahold of one.
I'd been wondering how the seat tube angle (~72deg) would affect handling, but no longer think it'll be a problem. Having the seat post pivot at an angle effectively couples yaw and pitch (which is bad) but the horizontal pitching pivot will rotate when I yaw in turns so I don't have to worry about lifting the rear tire. What I'll feel is the position of the pitch pivot moving vertically as I yaw, changing the angle of the trailer to the bike, affecting the wheelbase. I haven't ran the numbers but my eyeballs are telling me that we are dealing with a sine function with changes of small fractions of an inch for the first ~15 degrees of yaw, which I believe will be acceptable. This is because there's such a short distance between the yaw pivot and the pitch pivot.
I'm working on an alternate design right now that has more distance between the pivots (but requires no machining!) so there may be a bigger effect with the new design. Right now I've only got the new design in some 3d modeling software so I can't post pictures. I could post a rendering tomorrow if you don't want to wait until the weekend to see the new design.