Seatpost shims - thoughts?
Having never used one before, I am looking for a little guidance please?
My LBS says that they are crap and should be avoided at all costs?? They say that they can cause the seat post to wobble and can cause problems when fitting a carbon seatpost into a carbon frame, which is what I am thinking about doing.
But I want to fit a 27.2 seatpost in a 31.6 seat tube. As I see it I have two options, either the Cane Creek aluminium one at 75mm long or the U.S.E. high grade "plastic" one at 100mm.
From an engineering point of view, the longer the shim the better has to be the case, but I am not sure about the material?
The only reason I am considering this option is purely down to cosmetics I am embarrassed to admit. The correct sized 31.6 Ritchey WCS carbon seat post has much longer & larger logos on either side of the seat post compared with the 27.2 option, 30mm difference in actually fact. As I don't have a lot of seat post exposed (140m) when the 31.6 seatpost is fitted part of the logo (20mm) is covered by the seat tube, IMHO this looks pretty naff. In saying that, what will a thin seat post look like in a frame that has large OD tubes?
Consequetly I either say sod it and buy the correct sized post and ignore the issue about the logo, or go for the 27.2 option and fit a shim. Or maybe......fit another make? But I have the Ritchey WCS carbon bars and matching stem fitted already, so it would be nice to keep it all the same.
Any thoughts?
My LBS says that they are crap and should be avoided at all costs?? They say that they can cause the seat post to wobble and can cause problems when fitting a carbon seatpost into a carbon frame, which is what I am thinking about doing.
But I want to fit a 27.2 seatpost in a 31.6 seat tube. As I see it I have two options, either the Cane Creek aluminium one at 75mm long or the U.S.E. high grade "plastic" one at 100mm.
From an engineering point of view, the longer the shim the better has to be the case, but I am not sure about the material?
The only reason I am considering this option is purely down to cosmetics I am embarrassed to admit. The correct sized 31.6 Ritchey WCS carbon seat post has much longer & larger logos on either side of the seat post compared with the 27.2 option, 30mm difference in actually fact. As I don't have a lot of seat post exposed (140m) when the 31.6 seatpost is fitted part of the logo (20mm) is covered by the seat tube, IMHO this looks pretty naff. In saying that, what will a thin seat post look like in a frame that has large OD tubes?
Consequetly I either say sod it and buy the correct sized post and ignore the issue about the logo, or go for the 27.2 option and fit a shim. Or maybe......fit another make? But I have the Ritchey WCS carbon bars and matching stem fitted already, so it would be nice to keep it all the same.
Any thoughts?
"You only need two tools: WD40 and duct tape. If it doesn't move and it should, use WD40. If it moves and it shouldn't, use duct tape"
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Comments
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I 've been using a USE shim in my carbon frame for exactly the same reasons as yourself - the choice and cost of 27.2 posts is considerably better than 31.6mm - and I've had no problems - but there are some advantages: The smaller diameter post will be more compliant; many composite frames have an aluminium liner in the seat tube - the shim prevents any corrosion/sticking problems - assuming you use the USE acetal one. Good engineering practise is for a sleeve-fit of 3x diameter - anything more is redundant, so a 100mm shim is more than adequate for a 27.2mm post - particularly as a lot of post isn't showing.Make mine an Italian, with Campagnolo on the side..0
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Monty Dog wrote:I 've been using a USE shim in my carbon frame for exactly the same reasons as yourself - the choice and cost of 27.2 posts is considerably better than 31.6mm - and I've had no problems - but there are some advantages: The smaller diameter post will be more compliant; many composite frames have an aluminium liner in the seat tube - the shim prevents any corrosion/sticking problems - assuming you use the USE acetal one. Good engineering practise is for a sleeve-fit of 3x diameter - anything more is redundant, so a 100mm shim is more than adequate for a 27.2mm post - particularly as a lot of post isn't showing.
Good reply, thanks.
Just to cover my arse I contacted Scott to ask their thoughts regarding warranty etc.
They have said that providing that I only used a USE shim then it would not present any problems. Which I was going to anyway, so off we go and spend more money! :oops:"You only need two tools: WD40 and duct tape. If it doesn't move and it should, use WD40. If it moves and it shouldn't, use duct tape"0 -
Shims are fine - arguably they are manufactured to better tolerances than the inside of the seat tube. In addition, they will be more compressible and will therefore be able to conform under pressure better than either the post or the seat tube.
USE are good because they sell in a lot of ID/OD combinations.
LBS is talking horse-poo. LBS's increasingly, in my experience, tell people that its bad unless its stock, and do that "suck in air - rub chin" thing that car mechanics do when all you need is a new silencer.
What do you expect from a 16 year old working Saturdays? (I'm projecting, ignore me)0 -
I ran a shim in my old Bianchi . No-one makes 31.4 seatposts, so I shimmed it to 27.2. Didn't have any problems.0
