Seat Post Incompatibility
 

I'd like to move my Brooks saddle back and forth easily from one of my bikes to the other, but they have different sized seat posts. One is 25.0 and the other is 26.5. I could shim the narrower post with sheet aluminum, but I wonder if anyone has a better, more elegant solution. Some day I might buy a second Brooks, but the budget won't stand it right now (I just bought a B-17N S for my wife's bike).

Unclamping the posts from the seat rails is not an option for quick changes.

Sheldon Brown says seat tubes can be reamed to take larger posts, but 1.5 mm seems like a dangerous amount to take off a seat tube.

That 26.5 post is problematic...

USE makes 25mm shims for 26.4 or 26.6, but no 26.5. I have no idea if the .4 or .6 will fit your frame.

Thanks! I should have known somebody has already made these. I may actually experiment with aluminum flashing shaped like the USE items till I come up with the right thickness.

If you decide to try one of the manufactured shims I would suggest that you try the larger of the two first. A too-large post simply can't be inserted, clamping down on a too-small post may cause seat tube damage. The same applies with any homemade shims you might try; make sure that the top of the tube slot does not close past parallel (or the ears if present don't touch ) or you may permanently distort the tube. If you can't quite clamp the post tightly enough some carbon assembly paste may keep the post from sliding down.

Thanks, I've shimmed handlebar stems but never seat tubes.

If you try your own shims be sure to leave enough of a flange or lip so that you don't lose the shim down the tube.

I think the best solution is obvious, get a second saddle. Andy

Some day....

I get that unclamping the rails isn't an option, but why isn't it an option? I unclamp a saddle to switch between bikes right now, it takes about 3 minutes total from start to getting it angled perfect and tightened on the new post.
Its cuz I don't want to spend $70 right now for another saddle. Seems like a lot cleaner and more secure option vs shimming with home made or illfitting shims.
Hopefully someone on the wide web makes a shim that would fit properly.

I'll swallow my pride and admit that both my bikes (and my wife's bike) have the cheap, department-store-style seat post clamps, although the seat posts are alloy. Getting the rails into and out of these clamps is a major frustration. I should upgrade to the better seat posts with micro-adjust, but seat-angle adjustment has never been a big problem for us. We tend to keep all our seats dead horizontal.

Also, 3 minutes doesn't sound like a long time, but for me (the only one interested in bike maintenance) it's in addition to inflating tires, tightening loose stuff, fooling with helmet straps, and the other pre-ride necessities. Sometimes it's a wonder we ever get on the road.

I recently built an old frame into a fixed-gear bike and prefer it as a short-distance commuter. I prefer my geared bike for longer, hillier rides. The ancient Selle Royal saddle on the fixie is no fun, even on short rides.

I love my wife, but oh, that B-17!

With A Kalloy Plain seatpost on both bikes and a separate saddle clip, ( Brompton's ($30) Pentaclip is the best)
you can slip the saddle clip off the post top and move It.





yes standard seat post , and frame bores are Increasing in even Increments, 0.2mm at a step , so the 26.5 is likely a measuring error.

USE [UK] precision machines their seat post sizing shims, they made a 25.0 seat post and a 27,2 seat post and sold shim sleeves to use the smaller

seatposts in all the sizes in between.

[ The Shim thickness difference is 1/2 the difference in diameter , 26,4-25,0= 1.4 , so shim stock thickness has to be 0.7mm ]

Might need an accurate digital caliper, they are not that expensive with China making them, too.

Couldn't you get one of those cheap, knock-off, Brooks saddles to hold you over until your ship comes in? I like having two saddles for my two bikes.

You are absolutely right - I have a cheap (from India, not China) vernier caliper that's imprecise. Also, the smaller (I thought 25.0) seat post dates from the '70's and fits my Raleigh frame, also circa 1970. The advantage of fooling with home-made shims is you can find the right fit by trial and error. Once done, it's done. (I do need a better caliper.)

The Kalloy and Brompton products sound like the ideal solution, if I can get the right diameter post(s).

Has anyone ever been happy long term with a cheap knock-off of a Brooks? I rank the Brooks second only to the bicycle among humankind's greatest inventions. BTW, I have an Avocet super-gel something-or-other that came with the geared bike. No good on long rides. May have led to the previous owner's selling the bike.

I didn't say stay with it. Honestly, you'll have the money for the real deal LLLLOOONNNGGGGGG before that Brooks breaks in. Haha

My AlAn road & Cross Supers .. they used a 25.0 seat post, standard OD aluminum , thicker Tube Wall ..

sold the frame, to a taller, racer.. , still have 2 Campagnolo record seat posts ..