Bicycle Mechanics - Measuring seatpost diameter.

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jcivic00
07-02-03, 07:38 AM
I'm getting ready to fix up an old road bike, How would you measure the seatpost, inside diameter? or circumference?

a2psyklnut
07-02-03, 07:51 AM
Usually the existing seatpost is stamped with the size. It's usually something like 26.8 or 27.2 or something similar. It represents the diameter is metric measurement. If you can't find a stamped number, use a venier caliper to measure the O.D. of the seatpost, or the I.D. of the seatube.

L8R
L Lortami
07-02-03, 10:29 AM
just take a mesuring tape, and mesure the distence aroun the post.

SteveE
07-02-03, 10:41 AM
Originally posted by L Lortami
just take a mesuring tape, and mesure the distence aroun the post.
Dude, he wanted diameter not circumference.

EevetS ;)
doonster
07-02-03, 03:52 PM
You want diameter, to the nearest 0.1mm (those sizes are in mm). There are a few "standard" sizes - 27.2mm the most common on steel frames road bikes.
John E
07-02-03, 05:44 PM
The best solution is to borrow or buy a calibrated caliper. A cheap plastic one with a tolerance of +/- .1mm is adequate for this task. You also may want to consult Sheldon Brown's website, where he has started to compile a list of seat post diameters by bicycle model and brand name.
John E
07-02-03, 05:48 PM
Originally posted by SteveE
Dude, he wanted diameter not circumference.

Just divide by 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706 79 ...

Sorry ... I just wanted to see if I still knew it ...
Richard D
07-03-03, 03:08 AM
Any ideas on whether your likely to do any harm running a 30.8 post in a tube specced for 30.9 if the clamp holds the post firm?

Richard
dexmax
07-03-03, 03:37 AM
Originally posted by Richard D
Any ideas on whether your likely to do any harm running a 30.8 post in a tube specced for 30.9 if the clamp holds the post firm?

Richard

If the bolt(locking clamp) doesn't bend, it would be fine. If it does(bend), it would take so much effort to tighten them and the thread will be ruined..