Short seatpost shim - dangerous?

The reason for the amount of insertion into the frame is so that enough of the tube is supported.
The shim is used to make up for a slight difference in tupe/post sizes, usually only a few
thousanths of an inch. It is simply for the purpose of tightening the frame tube around the post.
Rarely more than the top inch or so of the frame tightens around the seat post even without a shim.

As long as you have at least the minimum amount of seat tube inside the frame, you should be fine.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": geocities.comczcornerOpen ↗

"Jean" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

I just bought a new seatpost for my road bike, but I need to use a shim

for

Quoted message said:

it to fit the seat tube (25.4mm post => 26.0mm seat tube inner diameter).

The local bike shop has a shim available, but it is only about 48mm long.

I

Quoted message said:

vaguely remember that the minimum seat post insertion is supposed to be at least 2.5 times the
seat post diameter ...which, in my case, yields a minimum insertion of 65mm.

Also, the short 48mm shim would not extend below the welds on the seat tube -it would have to be
at least 52mm long to extend below all the

welds.

Quoted message said:

Will using the "too short" shim unduly stress the seat tube (steel) and/or the seat post
(aluminum)? Would the post wobble in the tube if subjected

to

Quoted message said:

heavy load?

I agree that sounds marginally unsafe. Since 26.0 posts are very available in 350 and 400 mm ( they
only cost twice what the liner did!) why not get the right part??

Selling you a 25.4 post for a 26.0 frame sounds like a case of ignorance at the bike shop in the
most magnanimous reading. . .

--
Andrew Muzi yellowjersey.orgyellowjersey.orgOpen ↗ Open every day since 1 April 1971

A Muzi said:

"Jean" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

I just bought a new seatpost for my road bike, but I need to use a shim

for

Quoted message said:

it to fit the seat tube (25.4mm post => 26.0mm seat tube inner diameter). The local bike shop
has a shim available, but it is only about 48mm long.

I successfully make shims out of mylar (some 'plastic'😉 film. Very cheap, if you only find a source,
and easy to trim. I even mailed some out to a friend in Malaysia, to his full satisfaction.

It comes in sheets. So, any size is available.

Sergio Pisa

Quoted message said:

A Muzi wrote:

|"Jean" <[email hidden]> wrote in message
|
| I just bought a new seatpost for my road bike, but I need to use a shim
for
| it to fit the seat tube (25.4mm post => 26.0mm seat tube inner diameter).
|
| The local bike shop has a shim available, but it is only about 48mm long.
I
| vaguely remember that the minimum seat post insertion is supposed to be at least 2.5 times the
| seat post diameter ...which, in my case, yields a minimum insertion of 65mm.
|
| Also, the short 48mm shim would not extend below the welds on the seat tube -it would have to be
| at least 52mm long to extend below all the
welds.
|
| Will using the "too short" shim unduly stress the seat tube (steel) and/or the seat post
| (aluminum)? Would the post wobble in the tube if subjected
to
| heavy load?

Quoted message said:

I agree that sounds marginally unsafe. Since 26.0 posts are very available in 350 and 400 mm ( they
only cost twice what the liner did!) why not get the right part??

Quoted message said:

Selling you a 25.4 post for a 26.0 frame sounds like a case of ignorance at the bike shop in the
most magnanimous reading. . .

Quoted message said:

Andrew Muzi

I bought the seatpost (via mail-order) because it has zero set-back --which I need for proper fit.
The post is only made in two diameters - either 25.4 or 27.2, and it comes with a shim of your
choice. Unfortunately, the supplier did not have any 26.0 shims. Hence my search for a shim at my
LBS. Sooo, neither the seller nor I have made any mistakes ... yet ...

Jean

Ken said:

Needed to replace my seatpost on my roadbike. It has a strange diameter of 28mm.

.............

Quoted message said:

Sorry got carried away with my reply,

This is the last time I post about shims. Promise!

Why don't you guys give up depending on fancy-looking and apparently high-tech solutions?

First of all any aluminum seatpost can be somewhat reduced in diameter by polishing. Next, get
yourself some mylar film to make all possible shims. Here is a reprint of private correspondence
with a friend in Malaysia, to which I mailed mylar shims in fact ... .

Sergio Pisa
_____________________________________________________________________________
Hi Sergio, Still using the shim... on second bike. Excellent!

One thing good about the shim is that it's much easier to handle than metal that have sharp edges
that cuts. Regards, KW
_____________________________________________________________________________

Quoted message said:

Any suggestions as to what kind of store I should call for mylar sheets? Thanks,

1) A good hardware store;
2) a shop that overhaules, and rewinds, electric motors;
3) any high-tech (University, perhaps) experimental lab.

If you can't locate it send me your address and postage refund so that I can mail it to you. I got
about one square meter of it ... .

Sergio Pisa

"Sergio SERVADIO" <[email hidden]> wrote in message
"]news:[email hidden]...
| > Any suggestions as to what kind of store I should call for mylar sheets? Thanks,
|
| 1) A good hardware store;
| 2) a shop that overhaules, and rewinds, electric motors;
| 3) any high-tech (University, perhaps) experimental lab.
|
| If you can't locate it send me your address and postage refund so that I can mail it to you. I got
| about one square meter of it ... .
|
| Sergio Pisa
|

Thanks for the advice. I'll try to find some locally, and if that fails I'll contact you.

Jean

You may want to try a stationary shop.

The mylar that Sergio sent me looked like the thickest transparency sheet used for projection. Trust
that 3M ones will be robust enough.

No seat post slippage nor worries about metal fusing together. I've used the mylar set up in rain
and no water seeped into the seat tube. The mylar has some compression, which is good.

Regards, KW Mui

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Quoted message said:

Any suggestions as to what kind of store I should call for mylar sheets? Thanks,

1) A good hardware store;
2) a shop that overhaules, and rewinds, electric motors;
3) any high-tech (University, perhaps) experimental lab.

If you can't locate it send me your address and postage refund so that I can mail it to you. I got
about one square meter of it ... .

Sergio Pisa