So I've ordered a RS Reverb AXS for my Stanton Sherpa but the only place that I could get one was from the states.
Since I've ordered that I've also decided to change my frame to a Banshee Paradox, the Banshee has a 31.6 and the Sherpa runs a 30.9, so my question is will a shim be ok? It's a long post - 30.9 x 170 so I'm nervous about unnecessary stresses on the frame or will a 100mm (USE most likely) shim be ok? The company in the states don't accept refunds (eBay) so I'm hoping it'll be ok as it cost a crazy £798 including import fees. I could always sell it on if I need to but I don't really want to lose too much money on it.
Thoughts greatly appreciated. Thanks
Hmmmm
I just trashed a carbon post using an aluminum use shim in a carbon road frame. Was same as you, 30.9 to 31.6 and a fairly short post too at 350mm set way lower than minimum extention.
Shim deformed into the frame seat tube slot and gouged a huge chunk out of my Easton 90 post.
Pretty miffed I was.
Is the new frame carbon or alloy? Been using a 100mm shim with a reverb in an alloy frame for years. Just used some carbon past for added grip. No issues.
Drop Keith an email at Banshee through the info email. He's based in the UK and super helpful!
I've been using shims in aluminium frames for a couple of decades without any problems. You need a shim that is at least as long as the minimum insertion depth of the frame - basically long enough to extend beyond the top tube in a traditional frame. I've always found 100 mm shims to be fine. Giant used to ship bikes from the factory with 27.2 mm posts and shims to fit a 30.9 mm seat tube.
Carbon frames, I have no idea.
I’ve used shims in Alu and carbon frames for years, normally a USE plastic one.
No issues. Ever. Currently shimming a 30.9 AXS reverb in a 31.6 carbon seat tube.
+1 to what thols2 said. If I were splashing the cash on an AXS Reverb I’d probably go for a 30.9 and shim if necessary just to make sure I got maximum flexibility to switch between frames
I just trashed a carbon post using an aluminum use shim
One I have appears to be some kind of plastic, didn’t know they did an aluminium version
I think it depends on the frame. Most frames will have a minimum insertion depth to protect it from damage (which isn't the same as the posts' minimum insertion depth, which is separate and protects the post from snapping).
A frame's minimum insertion is generally something the manufacturer will tell you, but on standard double diamond hardtails it tends to be slightly below the lowest point of the seat tube/top tube junction.
As I understand it, the problem with shims is that any post below the depth of the shim isn't in contact with the seat tube and therefore doesn't count; the shim itself needs to meet the frame's minimum insertion.
It might be worth contacting your frame manufacturer to see if a 100mm shim will be okay.
-- Edit --
Sorry, not paying attention, Thols2 has already covered this!
I have one dropper post (Thomson, sk quite expensive and I cant afford one for each bike)
It's 27.2km.
It spends most of it's time in my 31.6mm Solaris with shim, occasionally gets moved to the Stinky, 30.9cm with a shim and very rarely in my El Mariachi, 27.2mm no shim.
Never had a problem with it, also its external so really easy to move between bikes.
Longest shim you can find is my advice, 100mm sounds sensible, IIRC that's what I use.
Thanks for the responses, so I reached out to Banshee and they said a shim but said 100mm shim would be pretty short so I need a custom made one or glue 2 USE shims together, cutting the rim of the second?
Does anyone know anyone that makes custom made shims at all?
"One I have appears to be some kind of plastic, didn’t know they did an aluminium version"
They use different materials depending on the shim thickness and length needed.
I've used shims in the past and they have been fine - not sure why this one killed the post but it was an expensive mistake. This was the first time I'd shimmed a carbon post in a carbon frame though. I have had a Thusbuster in my fatbike (alloy post, alloy frame and alloy shim) for years with no incident. I do take it out every few months to check.
If you're going to use two shims, you could trim the lip off one and glue it to the bottom end of the seatpost, then use the other one as standard. This will minimize the stress on the seatpost and frame, it will be pretty much the same as having the correct size seatpost.
Don't forget you are talking about a shim that is 0.35mm thick - someone isn't going to easily knock a 200mm long one up on a lathe. Shims for a 27.2 post are a different animal as they have a decent wall thicknesses.
You could just buy some stainless or plastic shim stock and glue it on.
I use a USE 30.9 to 31.6 shim, I've had no issues so far. I always use carbon paste on seatposts so I can use as little torque as possible to tighten the seat clamp