Seatpost strength: 27.2 vs 28.6

On Wed, 11 Feb 2004 02:15:04 GMT, "(Pete Cresswell)" <[email hidden]> may have

Quoted message said:

My hardtail has a 27.2 post shimmed to 28.6. My FS is 27.2.

I'm thinking about buying another post. Would a 28.6 post be significantly stronger than a 27.2? If
so, I might opt to give up the interchangability.

It would have more to do with specific material and wall thickness than diameter, at that level. I'm
sure there are some 27.2 posts that are stronger than some specific 28.6 posts. In other words, yes,
apples are more like rutabagas than an armadillo.

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Most alloy seatposts are very strong if used properly. Seatpost diameter has nothing to do with
strenght. It is related to the diameter of the bike's seat tube (wehre the seat post fits in) The
only post that will fit your bike, is the exact size that came with your bike. Two mm wider, and it
will not go in. 2 mm narrower, and you'll never be able to keep it tight.

If you want a stronger seatpost, you are in luck. the chapest seatposts are probably the stronger.
They are heavier. Most exspensive seatposts try to loose weight and they may get slightly more
flimsy. However, seatposts don't fail if properly installed, unless you go for the absurdly
expensive stuff, such as a look aero carbon seatpost. They do have a marking and you should never
install the seatpost with the marking showing. If you do, you may damage your bike. If your seatpost
mark shows on your bike, you need a longer seatpost. However, the diameter should remain the same.

Andres

"(Pete Cresswell)" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

My hardtail has a 27.2 post shimmed to 28.6. My FS is 27.2.

I'm thinking about buying another post. Would a 28.6 post be significantly stronger than a 27.2?
If so, I might opt to give up the interchangability.

On hardtails, the post also provides secondary compliance. IMHO if it isn't deforming, the flex may
be a welcome feature. For safety, replace every year or two just like bars. Tom

--
Bruni Bicycles
"Where art meets science"
brunibicycles.com
410.426.3420
andres muro <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Most alloy seatposts are very strong if used properly. Seatpost
diameter has nothing to do with strenght. It is related to the
diameter of the bike's seat tube (wehre the seat post fits in) The
only post that will fit your bike, is the exact size that came with
your bike. Two mm wider, and it will not go in. 2 mm narrower, and
you'll never be able to keep it tight.

If you want a stronger seatpost, you are in luck. the chapest
seatposts are probably the stronger. They are heavier. Most exspensive
seatposts try to loose weight and they may get slightly more flimsy.
However, seatposts don't fail if properly installed, unless you go for
the absurdly expensive stuff, such as a look aero carbon seatpost.
They do have a marking and you should never install the seatpost with
the marking showing. If you do, you may damage your bike. If your
seatpost mark shows on your bike, you need a longer seatpost. However,
the diameter should remain the same.

Andres

"(Pete Cresswell)" <[email hidden]> wrote in message

news:<[email hidden]>...

Quoted message said:

Quoted message said:

My hardtail has a 27.2 post shimmed to 28.6.
My FS is 27.2.

I'm thinking about buying another post. Would a 28.6 post be

significantly

Quoted message said:

Quoted message said:

stronger than a 27.2? If so, I might opt to give up the

interchangability.

Personally, I don't like shims. Why not just get the correct size?

Most seatpost failures I've seen are at the clamp, and the post diameter has no effect there.

-Dion

"(Pete Cresswell)" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

My hardtail has a 27.2 post shimmed to 28.6. My FS is 27.2.

I'm thinking about buying another post. Would a 28.6 post be

significantly

Quoted message said:

stronger than a 27.2? If so, I might opt to give up the

interchangability.

Quoted message said:

--
PeteCresswell

"(Pete Cresswell)" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

I'm thinking about buying another post. Would a 28.6 post be significantly stronger than a 27.2?
If so, I might opt to give up the interchangability.

right, it's all about the _wall thickness_ and _material quality_. if you want the strongest post,
get an iron one. it will probably never break, maybe bend, and will make your bike 2 pounds heavier
:o) aluminium posts are much lighter, even though they need significantly higher wall thickness, and
they will not warn you before they break. cf posts are the stiffest and lightest, I have never heard
any break, but probably they do sometimes :o)

Frank www.plitkorn.com

Quoted message said:

Would a 28.6 post be significantly stronger than a 27.2?

If they're the same material and wall thickness, then the larger post would have a bending modulus
greater than the smaller by a factor of

(28.6/27.2)^3

This 19% increase doesn't seem like enough to justify the change.