Are SeatPost Shims a Bad Idea..?

Quoted post said:

Originally posted by puma
I've got a 31.6 seattube and a 27.2 seatpost, which obviously calls for a shim. My question is what the disadvantages and/or advantages, if any, of this may be (like, I could imagine that the shims may prevent seatpost seizings...?)?

Thanks.

None either way.Unless the shim is an inert material seizings can still occur.

I use the shim from USE for my Colnago C50 28.0 frame to 27.2 seatpost, with no problems. It is a plastic material, and so would in fact help prevent seizing in metal frames.

I use a shim that I cut from aluminum Coke can on a LeMond Victoire Ti (27.2 frame) and an older Syncrose Ti seatpost, which was a 27.0, with no problems. (May not have need a shim at all, but it worked just fine).

What about for handlebars?

Quoted post said:

Originally posted by BaCardi
What about for handlebars?

I don't see why not... I personally would make sure if you were cutting down an aluminum pop can, cut it square, and to at least the width of the stem clamp.

Be carefull using a shim for handlebars, it is not a good idea. Think about the weight on the bars and a panic stop. It is one place where the right stem and bar should be used.

Quoted post said:

Originally posted by pudster
Be carefull using a shim for handlebars, it is not a good idea. Think about the weight on the bars and a panic stop. It is one place where the right stem and bar should be used.

Can´t see why a shim should be a problem unless it´s to convert road to MTB which is a no no anyway , mtb to road fits without any messing about .

Quoted post said:

Originally posted by puma
I've got a 31.6 seattube and a 27.2 seatpost, which obviously calls for a shim. My question is what the disadvantages and/or advantages, if any, of this may be (like, I could imagine that the shims may prevent seatpost seizings...?)?

Thanks.

A very bad idea. Seat posts are very cheap. Buy one.

my new 2004 Giant VT1 came with a shim for the rather tacky looking Ritchey seatpost. I was rather surprised at this and can't see any reason for it. It seems to work OK though and didn't break when i crashed and broke my shoulder!

Colin (must change username to brokenshoulder as wrist now mended)

Hi Bititanio,

Quite excited when I hear that a 27.2 - 28mm shim does exist for Colnago C40/C50. I have always tried to find an appropriate shim so that I could install a Look Ergopost on my C40 and set my seat way back for more power output.

Does the shim of only 0.4mm thickness works OK on your C50 ? Also wonder whether the shim could be ordered directly from USE or not.

Quoted post said:

Originally posted by Deanster
A very bad idea. Seat posts are very cheap. Buy one.

It would be very helpful to inform us as to why you have reached this decision. Thanks.

Quoted post said:

Originally posted by el Inglés
Can´t see why a shim should be a problem unless it´s to convert road to MTB which is a no no anyway , mtb to road fits without any messing about .

MTB to road does not really 'FIT'. mtb is 25.4 standad road is 25.8/26.0. People get awy with it,but some stems and clamps are more acomodating than others,but it still should not be done.

Quoted post said:

Originally posted by puma
It would be very helpful to inform us as to why you have reached this decision. Thanks.

It's not necessarily a bad idea,they do work, and he/she is just blowing hooey.

I'm actually refering to installing an X sized road bike seatpost into a Y sized road frame seat tube. If I get the proper sized shim, I can't see it being a problem...?

I had a USE seatpost at one time that was 25.4 shimmed to 26.8 and it worked fine. It was a precise shim made for the application. No problems.

I also tried shimming handlebars with home-made soda can shims once and it SUCKED. The bars were always creaking and coming loose. I wound-up just getting the correct bars for the stem. Much better.

Quoted post said:

Originally posted by boudreaux
MTB to road does not really 'FIT'. mtb is 25.4 standad road is 25.8/26.0. People get awy(?) with it,but some stems and clamps are more acomodating than others,but it still should not be done.

In this I go by what my cycle shop guy says , and he seems to know what he´s talking about , but he does not recommend it on the ultralight or carbon bars .
The biggest problem is that stems in the +6/-6 design are difficult to get in 135 mm except in the expensive groups . I´ve got a 3t-the and a ritchey that´s off ( and on at times ) a mtb , both work fine , no problem nor damage to the bars .

BUT do ask a professional for advice about this sort of mix and match if you have any doubts , and I don´t mean on a forum - this is hands on stuff .

Quoted post said:

Originally posted by puma
It would be very helpful to inform us as to why you have reached this decision. Thanks.

Look at the size differential. 27.2 to 31.6 is 4.4mm. If you don't get a perfectly round insert you that extends well into the seat tube you will be putting an unusual stress on the seatpost or won't be getting the friction necessary to stop the seat from moving. I have used Coke cans and Red Bull can for shims on small differences in frictional surfaces requiring filling, but...
Also, I would never use anything on carbon parts that would put any potential point stress on a carbon part. Failures aren't a little bending of the part on carbon, but catastrophic in nature.

Quoted post said:

Originally posted by boudreaux
It's not necessarily a bad idea,they do work, and he/she is just blowing hooey.

Please read my reply to the question asking for the justification for my answer. If you still think that it is hooey then...I really don't need to go any further do I...

I'ld actually be installing an aluminum Thomson or Syncros and the shim would be long enough to distribute and stress...but I do see what you're saying.