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I've noticed recently in the Chinese markets that shims have started appearing for 30.9-31.6mm dropper seatposts.
You can go bigger, but not smaller obviously. This kind of puts your money on the smaller diameter seatpost in case you change frame later on. If you buy the larger diameter post then you're restricting yourself.
Have these managed to reach the UK market yet?
Ps. I have one of these still in the packet at home. I bought a 30.9 dropper post and shim and then the 31.6 frame I was after went out of stock and I managed to get a new run 30.9 different one.
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.
A lot of Giant bikes used to have 30.8 mm seat tubes with a shim and 27.2 mm seatpost as standard.
Those shims in the pictures look pretty short. I've always taken 100 mm long as the minimum. Good quality shims aren't expensive, no point buying a cheap one that's too short.
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.
Seat post shims aren’t new, they’ve been around forever. I’ve had USE and brand X ones on my bikes.
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.
I've not had a dropper post last long enough to worry about it TBH.
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.
That said, I'm using an alu shim for the dropper in my HT right now! I've had that shim for 10 years and dug it out especially.
Yep, shimming is as old as engineering itself.
My EBB is shimmed with a bit of coke can.
I used a 27.2- 30mm shim to fit my gravity dropper into my 2002 Kona Bear
Shims have been around for yonks
The Bear frame hangs in my garage and the Gravity Dropper is now on my hardtail (it's a bit rattly but still works fine)
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?
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'm pleased you've been successful running your shim as long as you have, but your population sample size is one and its not always the case.
Op, I've got some sad news about Joe Cocker... 😉
I run a 27.2 dropper in a 31.6 frame with a shim as it's the only way with a small frame with a curved seat tube that I could get one to fit. Works perfectly but at 56kg I believe I might be at the lower end of the stw demographic
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
Specialized shim a 31.6 post to tehir 34.whatever seat-tubes out the factory...
DrP
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.
What Thols2 said, I've not had a seatpost shim slip in decades of using them, they've all had a lip around the top.
Unless a 31.6 seatpost was an absolute bargain for some reason I can't really see the point in not shimming a 30.9 post to fit.
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.
Only thing I’d add is I always look for a shim at least 100mm long. Always worked fine for me.
Hardly. It’s not even 50% of potential dropper post sizes…
Have these managed to reach the UK market yet?
Nah, we're still waiting for the 1990s 🙂
https://www.sjscycles.co.uk/search/?term=shim
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.
@desperatebicycle the reviews on the Brand-X/Use shims go back six years. I honestly hadn't seen this particular size available. But back then I was in a desert country with next to zero riding. Back home in 2018 I got my retro bikes out of storage to play with. Then 18 months later I'm out again in a country which comprises mostly of roadies where two wheels are cocnerned. The vast majority of riders here only use S or M sized frames too. A fair proportion of the popilation are too short even for a 15" seattube.
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.
@mrdestructo
don't pick on me! I'm just joining in with the general theme 😉
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.
I’ve got a USE shim in my 1998 Club Roost VCV…
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.
One of my bikes is 30.9 and uses a shim permanently - it has never moved!
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