jdms mvp

followup question:
so do i buy a stated "27.0mm" seat post for a 27.mm seat tube? intuition would tell me that it wouldn't work because the inner diameter of the tube and outer diamter of the post are the same?

can someone educate me?

-Nathan






for a 27mm seat post diameter tube is possible to use a 27.2mm tube. the measurement "appears" to be miniscule, but would this work?

on the flip side....will a 27.0mm post work in a 27.2mm tube and properly clamp or tighten?

thanks in advanced

mathletics

No.

jdms mvp

no to both questions?

dirtyphotons

get it right. i've ruined a frame and cracked a seatpost over a .2mm difference.

jdms mvp

ahh thanks

mathletics

Yes, no to both questions. Seatposts come in 2mm increments from 25mm to 30whatever for a reason. Get the right one.

jdms mvp

will do. thanks for the quick responses.

lvleph

There are shims, that will allow one to use a 27mm seat post in a 27.2 seat tube.

jdms mvp

so do i buy a stated 27.0mm seat post for a 27.mm seat tube? intuition would tell me that it wouldn't work because the inner diameter of the tube and outer diamter of the post are the same?

can someone educate me?

-Natha

mander

Nope it'll be fine. It's supposed to fit snugly. Any other way is bad.

Remember to grease the seatpost before installing it.

crushkilldstroy

They're called beer cans.

jdms mvp

so when a bike manufacturer states 27.0mm on their post it'll be a tiny bit smaller than 27.0mm to fit in a 27.0mm tube?

dirtyphotons

when manufacturers list the "size" of the seatpost they're referring to the outer diameter of the tube. when they list the "size" of a seattube, they're referring to the inner diameter of the tube. they should be exactly the same.

jdms mvp

well the questions i'm asking is if a Inner diameter and out dimeter are the same, then in theory* one pipe should NOT be able to fit in the other...

dirtyphotons

in theory, if one pipe has the exact inner diameter as the outer of another. they will fit inside each other with exactly no play. what theory are you using?

jdms mvp

yea maybe i'm incorrect? i'm just asking someone to educate me

starting to make more sense to me

Aeroplane

In theory, yes. But those sizes that are printed aren't exact. In fact, there will be deviation in thickness between seatposts of the same "size" even by the same manufacturer. These are called "tolerances", and everybody takes them into account for you.

Surly has a little essay on their site that covers this in detail. Read and be educated.

So just match the numbers.

jdms mvp

thanks for the link