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To shim or not to shim, that is the question?(11 posts)

To shim or not to shim, that is the question?Iwannapodiumgirl
Aug 19, 2002 3:55 AM
Still umming and ahhing over that carbon post. Further chats with riding mates about the issue, led us to ponder -"carbon post - to shim or not to shim"?

If requiring a 27.2mm post, is it preferrable to a) buy a 27.2mm carbon post and cross everything, b) buy a 25mm carbon post with a shim and cross everything, c) stick to good ol' titinanium or aluminium for that true Pave experince or d) none of the above.

Am considering the USE Carbon Alien - any comments/concern on this seatpost?

Thanks in advance guys and girls!
Addendum # 1....Iwannapodiumgirl
Aug 19, 2002 3:58 AM
I guess I could also consider a 27.0, 26.8, 25.0 USE Carbon Alien seatpost with shim... which is preferable? :o)
Addendum # 1....clintb
Aug 19, 2002 7:09 AM
Just having went through this I can offer some insight into the USE products.

1. USE only offers the carbon posts in 25.0 and 27.2.
2. If you go with 25.0, their shim is about the only one that I've found in 25.0 to whatever size.
3. A USE carbon post in 27.2 shimmed up gets you a UPVC (basically plastic) shim that literally KILLS creaks and squeaks. This assumes you use their shim.

What post do you have now and does it use a shim?
Addendum # 1....Iwannapodiumgirl
Aug 19, 2002 2:58 PM
According to the Australian distributors website, the seatpost comes in those additional sizes, but will check that out.

I am concerned with reducing creaks and squeezes as well as slippage and breakage. Will the shim help reduce this?

I will be using the USE shim. Did you buy the 25.0 and shimmy it up to a 27.0?

Was riding an aluminium seatpost.

Thanks
Addendum # 1....clintb
Aug 19, 2002 8:37 PM
If you look carefully at the USE site, they list additional sizes in the aluminum, but nothing on the carbon. In the US, you're really not supposed to be able to get the 27.2 in a 350, but through Bulltek Sports I was able to. The owner of Bulltek informed me that, the 27.2 x 350 that's offered here is gray market and he normally doesn't carry it. He made a call to USE USA and they sent out a 27.2 x 350 with a 27.2 to 31.6 shim. Apparently, the grey market ones don't carry a US warranty, but he confirmed that mine will. I grilled him on the warrany point to make certain.

If you get the shim for 27.2, then you'll eliminate creaks and squeaks. It's the 27.2 that's made of UPVC, not the smaller 25.0 shim. Either shim will reduce the chance of breakage as they're designed to put more even clamping around the post circumference. Just make sure to put the shim's slot forward. Regarding slippage...Do not grease a carbon post. Greasing a post is to keep similar metals like steel from rusting, or dissimilar metals from oxidizing. There's probably a better term for the oxidizing however. If you get the UPVC shim, no grease is necessary at all. The aluminum shim should however be greased between it and the frame.

So, what diameter post do you have now and is it a direct fit, or shimmed?

p.s. More than likely, you'll be using something in a 270 length. If so, ignore my stuff on the 350.
27.2 post - no shim...Iwannapodiumgirl
Aug 19, 2002 9:09 PM
I have an aluminium 27.2 seatpost, with no shim. The frame (a Bianchi XL EV2) is a 27.2 seatpost per manuf. specs.

Am considering the 25.0 post with 25.0 to 27.2 shim. If the shim assists in the longivity of the post, I am there!

:o)
27.2 post - no shim...clintb
Aug 20, 2002 10:00 AM
Ok, so that will make you use either the 27.2 w/no shim, or the 25.0 w/shim. Your frame is compact, right? If so, then length may be an issue as well. Most compacts need something longer than 270, so you'll be forced to go with a 350. Or, Time has a new carbon post in 27.2 x 300 with a honeycomb structure for strength. http://www.bikyle.com/Seatposts.asp

From the information I've gathered, it seems the shim is a way of compensating for "not so round" seat tubes. Throw into that mix some burrs and sharp edges that can score carbon and you've got stress risers and cracks. It's their way of creating a more controlled enviroment. A side benefit on my TCR is Giant can use a larger diameter seat tube and hopefully gain strength. It came stock with a 27.2 to 31.6 shim.

Honestly though, what are you trying to achieve with a carbon post? Since the UPVC shim isn't available for the 25.0, you'll more than likely have some squeaks and creaks. On the other hand you may not, but my luck wasn't so good with an aluminum shim. You may have an easier time with the titanium in 27.2.
Length no issue....Iwannapodiumgirl
Aug 20, 2002 3:10 PM
The frame is compact, yet not like the Giant TCR. I am using a 270 seat post at the minute, with only approx 15cm seatpost showing - it is a 55cm frame (52cm seat tube)
On my other road bike with conventional geometry I am showing 12cm of post.

Still thinking of getting the 25.0 seatpost with PVC shim - my LBS said he had heard of such a shim and will look into it... hopefully he is not going to get a piece of PVS plumbing pipe, write USE PVC shim on it in permanent marker pen, and sell it to me for a small fortune!

Thanks for the help clintb... will post my experience once completed.
Length no issue....clintb
Aug 20, 2002 6:21 PM
Ah, not as much slope I guess. Yeah, my large TCR doesn't have much either. Just the smaller ones I'm guessing.

Remember, the 25.0 to whatever shim is NOT UPVC, it's aluminum. Look here and it'll explain all. Oh, the shims are only about $12 USD.

Here's a small excerpt:
All shims are machined to very high tolerances from 6082 T6 Aluminum and larger sizes from a special filled engineering Thermoplastic (UPVC) to keep the weight down.

Later
re: To shim or not to shim, that is the question?Noam
Aug 19, 2002 5:53 PM
I read your posts with a lot of pleasure i like your style.

Carb. vs Ti. You know I still love the look of Campy Record aero seat post. Same goes for Campy Delta break clipers. Where are they?.

Noam
thanks Noam...Iwannapodiumgirl
Aug 19, 2002 7:48 PM
a simple comment like that makes my time on this board worth while!

Not sure where the aero poat or delta brake calpiers are, yet everything Campy looks great to me!