Seat Post Shims - Good, Bad? -

Discuss light weight issues concerning road bikes & parts.
User avatar
mellowJohnny
Posts: 484
Joined: Thu Aug 16, 2012 12:56 am
Location: YYZ

by mellowJohnny

Anyone out there have experience running a smaller diameter post in a larger frame with a seat post shim?

My SuperSix came with a 31.6 post which I'm about to replace. Two questions:

**Edit**
1) In general does a 27.2 post weigh less than the same post in 31.6? Hard to tell browsing the web as the claimed weights are usually for just one size. Seeing as how the USE thermoplastic shim is a claimed 25g, it would seem that a 27.2 post w/ shim would be the way to go if the weights are substantially different.

2) Will it suck? My LBS said "don't do it", claiming in their experience the bottom of the post (I assume the bit sticking out past the shim) will rattle around in the frame.

I have a nice EC90 post from an old steel bike I'd love to run as it is 171g (uncut) + 25g shim would give me a decent weight post for "free".

Looking for feedback!
Last edited by mellowJohnny on Mon Sep 17, 2012 6:06 pm, edited 3 times in total.

coppercook62
Posts: 383
Joined: Mon Nov 15, 2010 7:58 am

by coppercook62

I have a 08 Cervelo R3 which was a real wiered size. I went to 27.2 and have never had a issue with it. Never had heard any ratteling that your LBS has described. I do have a Di2 battery in seat post maybe that prevents it from ratteling.

5 8 5
Posts: 1353
Joined: Sat Jul 29, 2006 2:36 am
Location: UK

by 5 8 5

I've been using a USE thermoplastic 31.6 to 27.2 shim for 3 years in one of my frames without any problems. My frames aluminium and I didn't want to use an aluminium shim in case I had problems with it bonding to the frame and / or seatpin. I've had no bother with it. No creaking at all or rattling. I use carbon paste between the pin and shim.

tomgag
Posts: 44
Joined: Sun Jan 15, 2012 2:25 pm

by tomgag

I used to do in back in 90-tees with my first Giant TCR (silver and still have it) but as I loved that bike I would not use the shim now.

No need and do not see any reason. It gathers dust, dirt etc...since then no more shims.
IRONMAN 70,3 TARGET TIME 03:55

fitty4
Posts: 350
Joined: Mon Jul 13, 2009 9:19 pm
Location: Denmark

by fitty4

I also use the USE themoplastic shim and have being doing so for a year. No issues at all!

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric

I have the USE shim in my PedalForce QS2. I prefer 27.2mm posts and the shim works great. The one drawback is that there's a small gap in the shim and if you ride in the rain small amounts of water and grit can go down it. It's no big deal just ends up with more crud than a regular non shim installation. I've infrequently run rags down the seat tube to clean it up.

User avatar
mellowJohnny
Posts: 484
Joined: Thu Aug 16, 2012 12:56 am
Location: YYZ

by mellowJohnny

Excellent - thanks for all the replies - I will order up a USE shim and see how it goes.

Thanks!

boolinwall
Posts: 195
Joined: Thu Aug 23, 2012 11:19 pm

by boolinwall

The biggest advantage to a 27.2 post isn't even the weight savings. It's the added comfort. 31.6 posts are much harsher riding than 27.2 (in an equal post, please don't compare a carbon 31.6 to an alloy 27.2)
I used to use the USE shim on my scapin. No issues at all. If you have fibre grip or another such carbon paste around, use it. It helps. Also, if you turn the slot so it faces the front of the frame, you won't get as much crud in it.

User avatar
HammerTime2
Posts: 5433
Joined: Thu May 04, 2006 4:43 pm
Location: Wherever there's a mountain beckoning to be climbed

by HammerTime2

mellowJohnny wrote:1) In general does a 27.2 post weigh less than the same post in 31.6? Hard to tell browsing the web as the claimed weights are usually for just one size. Seeing as how the USE thermoplastic shim is a claimed 5g, it would seem that a 27.2 post w/ shim would be the way to go.
Where are you getting a weight of 5g?
http://www.use1.com/product/2/000062/seat-post-shims/ wrote:SSX316 27.2 31.6 Thermo Plastic 26
That's a manufacturer's claimed weight of 26g for a 27.2 to 31.6 shim.

So 25g per FWB. Either way, that's not 5 g.

Your figure of 5g appears to be based on the 25.0 to 25.4 or 27.2 to 27.8 aluminum shims, which are listed at 5g.

User avatar
SWijland
Posts: 853
Joined: Tue Aug 08, 2006 1:41 pm
Location: The Netherlands
Contact:

by SWijland

My USE thermoplastic shim (31.6-27.2) worked like crap. Had to tigthen it in ways that didn't feel safe to prevent tbe seatpost from slipping. I am now using a no name alu shim and it works great.

thisisatest
Shop Owner
Posts: 1980
Joined: Sat Jun 13, 2009 4:02 am
Location: NoVA/DC

by thisisatest

Thermoplastic shim is slippery, especially against use's own hard anodised shockposts. But now there is grip paste (carbon paste, fiber grip, whatever), so that should be a non-issue now.
31.6-27.2 should pose zero "rattling" issues inside the frame, the gap inside is too big to have the post touch the seattube inner walls. It sometimes happens with long posts in certain frames without any shim...
Another reason the USE shim is a good choice is its insert depth-100mm i think.

User avatar
mellowJohnny
Posts: 484
Joined: Thu Aug 16, 2012 12:56 am
Location: YYZ

by mellowJohnny

HammerTime2 wrote:
mellowJohnny wrote:1) In general does a 27.2 post weigh less than the same post in 31.6? Hard to tell browsing the web as the claimed weights are usually for just one size. Seeing as how the USE thermoplastic shim is a claimed 5g, it would seem that a 27.2 post w/ shim would be the way to go.
Where are you getting a weight of 5g?
http://www.use1.com/product/2/000062/seat-post-shims/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; wrote:SSX316 27.2 31.6 Thermo Plastic 26
That's a manufacturer's claimed weight of 26g for a 27.2 to 31.6 shim.

http://fairwheelbikes.com/use-seatpost-shim-p-1235.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; wrote:27.2-31.6, 25g (delrin)
So 25g per FWB. Either way, that's not 5 g.

Your figure of 5g appears to be based on the 25.0 to 25.4 or 27.2 to 27.8 aluminum shims, which are listed at 5g.


I liked the 5g weight better :-). But as they say, reality is what does not go away even if you choose to ignore it. Thanks for the correction.

User avatar
mellowJohnny
Posts: 484
Joined: Thu Aug 16, 2012 12:56 am
Location: YYZ

by mellowJohnny

thisisatest wrote:Thermoplastic shim is slippery, especially against use's own hard anodised shockposts. But now there is grip paste (carbon paste, fiber grip, whatever), so that should be a non-issue now.
31.6-27.2 should pose zero "rattling" issues inside the frame, the gap inside is too big to have the post touch the seattube inner walls. It sometimes happens with long posts in certain frames without any shim...
Another reason the USE shim is a good choice is its insert depth-100mm i think.



I'll try the paste for sure. I'm trying to reuse an old post here, so my investment is limited to the $10 shim. If it does not work out I'll sell the post. As for he "rattling" I thought the same thing - the gap will be way to big for that post to ever flex enough to hit the seat tube.

joohan
Posts: 2
Joined: Sun May 02, 2010 12:53 pm

by joohan

About the "rattling" a few members have been talking about. The length of seatpost under the shim, where there could be "rattling", is useless isn't it? It doesn't help support anything, so why not cut it of? Free weight saving...

User avatar
mellowJohnny
Posts: 484
Joined: Thu Aug 16, 2012 12:56 am
Location: YYZ

by mellowJohnny

You read my mind - that's what I'll be doing. Seeing as how I made a 20g miscalculation on the shim weight I'll be trimming the post and ordering a Ti EC90 bolt kit.

Update: just got the shim and it came in at 20g, 5g lighter than advertised. The surface is textured, plus carbo grip and we should be good.

Trimmed the post for another 10g off, bringing the whole thing to 181g. Ti hardware will bring it down to 170g. She ain't Schmolke light, but I can put the savings into other parts.
Last edited by mellowJohnny on Sat Sep 22, 2012 3:31 pm, edited 2 times in total.

Post Reply
  • Similar Topics
    Replies
    Views
    Last post