Yes, seatpost shims have been around for a while.
I did the exact same thing, buying a smaller diameter dropper for my next frame while my other one was awaiting warranty.

Are you saying that you’ve not been able to get seatpost shims until now? I’ve been buying/using them for what must be 15 years now, and I’m pretty sure they’ve been around a lot longer than that.

USE and cane creek make/sell them.

My 1997 Orange P7 came with a seatpost shim as standard so that you could use 27.2 mm.

I found a seatpost I could use without the shim so I threw it in my weird parts box.

Still got the shim though so if anyone ever produces a bike with a 29.6mm seat tube again I’ll be laughing.

Edit: I recently bought a stem shim so that I could try the Ritchey Kyote bars on my P7 (1997 was the last of the 1″ headtubes). Wasn’t to sure about it but I haven’t died yet.

Yep, shimming is as old as engineering itself.

My EBB is shimmed with a bit of coke can.

In the grand scheme of things I’d rather pay £200 for a new dropper and recoup some money from the resale of the old one than deal with the potential issues associated with shimming an undersized dropper

Issues? I’ve had a 150mm shimmed dropper in a bike for 5 years, it still works perfectly. What issues have I missed?

Op, I’ve got some sad news about Joe Cocker… 😉

USE suspension seatposts (late 90s) used to only come in a couple of sizes (something crazy like 26.2?) and then you shimmed it from there to your frame size. A lot more variance in seatpost diameters in those days so it made a lot of sense.

No idea why everything isn’t 35mm now – would make a lot of sense

I said potential issues, by which I meant potential slippage.

Shims add another slip plane wherever they are used and the combination of dissimilar materials that don’t grip each other well goes up and precise fit can be harder to achieve.

I think it’s easier to stop slippage with a shim. Shims have a lip on the top so they won’t slide down into the seat tube. You can grease the outside of the shim to make it easy to remove from the frame without any problem of it slipping. You can sand the inside of the shim (and the contact surface of the seatpost if necessary) with very fine sandpaper to remove the shiny finish, then degrease it. I find that if you do that, you don’t get problems of slippage. If you did that without a shim, you’d quite likely have a problem of the seatpost bonding to the frame and being impossible to remove.

It’s kind of ironic that dropper posts make shims actually good (since you don’t move the post much at all any more), but it seems like nobody uses them much any more. Whereas back when you manually dropped posts, shims were terrible and loads of people had them.

Hardly. It’s not even 50% of potential dropper post sizes…

I recently got a Brand X shim from CRC for £4 to fit a 30.9 post in my Starling, which has a bit of distortion in the seat tube making it difficult/impossible to full insert a 31.6.

Mildly annoying at the time, but in hindsight a wise move because it should also limit the potential for the post to fuse with the frame.

The OP will love it when he finds out you can watch telly in colour too 😉

Seriously, I’ve been using shims for about 20 years and I’ve never had an issue.

Yeah, been using shims for years, only time i’ve not been a fan is if the frame comes shimmed, like my old kona explosif, also some of the shims come oversized, so you have to either cut a little bit off lengthwise, or sand it down internally.

USE suspension seatposts (late 90s) used to only come in a couple of sizes (something crazy like 26.2?) and then you shimmed it from there to your frame size. A lot more variance in seatpost diameters in those days so it made a lot of sense.

it was 25.0 and 27.2. I have both…actually quite recent ones. One was on a 27.2 dia frame, the other is on a 31.6, both shimmed.

Rubber_Buccaneer
Only thing I’d add is I always look for a shim at least 100mm long. Always worked fine for me.

Agreed, though my current frame only specifies 80mm of seat post. I bought a USE one, as they seemed the longest (easily) available, at 100mm iirc. When I sent one dropper off for service I was able to move another across to my main bike with a shim. If you were spending the money on a RS AXS dropper (or any realistically), I’d buy the smallest & shim up if needed, so you could move it on to your next bike