Jameth

My 2015-ish Raleigh Back Alley uses the most annoying seatpost size on the planet - 25.6. I've already replaced the stock seatpost with a cheap Sunlite post a few years back, but now it also needs to be replaced. I want to replace it with a nicer 25.4 post, but can't find a shim that thin.

Any suggestions?

RCMoeur 

That should be a good recycle assignment for an empty aluminum pop or beer can. Might take 1/2 to 1 full diameter wrap - as I recall, they're about 0.11 to 0.14 mm in thickness. I did something similar with my Raleigh Pro and it's been as solid as a unshimmed assembly.

Rick

You could also go see if a local machine shop has some shim stock. 1mm = .0394"

Duragrouch

Beat me to it. It also cuts easily with scissors without dulling them. I've used to shim the outside of a bushing for a better fit. Make the shim as long (deep) as you can, it will keep the seatpost straighter in the seat tube, plus you'll have enough for sufficient to stick out to grab with your finger and/or tape it to keep it from dropping into the seat tube when loosening the clamp.

grumpus

If you have a friendly local machine shop, ask for some 0.004" shim stock, or they could even turn down a slightly larger seatpost to fit. Or just bodge it with a Coke can like everyone else - be sure it reaches an inch or two below the top tube, or you could break your frame. If you're going to be adjusting the saddle height on the fly, carry a spare shim for when it falls down inside and you can't fish it out.

Duragrouch

(above) Turning down a slightly larger seatpost: a) Only if taking off very little material, because otherwise it's a much thinner wall than designed, and b) that final turning cut on the lathe better be at very slow feed to have a really smooth finish; Any circumferential grooves will be fatigue crack initiation points when the tube is under bending load under rider weight.

JoeTBM 

I agree that 25.6 is not a common size but they are out there.

I'm just curious why you are replacing seat posts. What is the issue why your seat post needs to be replaced?

I just googled the part and found these offerings in 25.6

https://www.modernbike.com/seatposts+diameteris25.6-

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p4432023.m570.l1313&_nkw=seat+post+25.6&_sacat=0

Jameth

The clamp is bent and corroded, as are the rails on my B17. So, I also have to replace the saddle, which I haven't been too happy with in the first place. I've been experiencing a lot of pain and discomfort. Recently, the nose on my saddle rocked up during one of my long commutes which made the problem even worse.

I'm considering a C19 Carved saddle and don't want to trust an expensive saddle (or my groin) to another cheap $20 seatpost. The Sunlite post you linked to is what I have now and the even cheaper Kalloy post doesn't inspire confidence. I also want 2-bolt adjustment, so I'm looking at the Thomson Elite.

JoeTBM 

Understood, thanks for the explanation. I have seen this happen with seat posts that are not fully torqued or the bolts loosen up causing the the saddle to first rock thus wearing the clamp.

sunburst

I've bought the Kalloy Uno for a couple of bikes and have years of service on one. And I bought it for the same reason, I needed 0.2mm more dia and got tired of the shim approach just to save a few $$ (which slipped a bit on me). The Kalloy also solved my setback problem on two bikes, both with Brooks saddles. I own a few each of B17 and B67 and I learned recently that the B67 has even shorter rails!

Aubergine 

For a shim, I recommend a steel can rather than aluminum. I use them on old French bikes that seem to have a 25.5 mm seat tube. The cans to look for have a rim on the outside of the lid, which helps them stay in place at the top of the seat tube. I prefer the Old Fisherman brand of roasted eel (Love that stuff) but tuna cans also will work.

Duragrouch

(above) Rim on top, brilliant.