Bicycle Mechanics - What OD is my seatpost?

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FarHorizon
08-08-05, 05:48 PM
I just put the calipers to my Easton aluminum-frame seat post (measuring for a front derailleur). I measure 1.28" (!). I've heard of one-and-a-quarter and one-and-three-eights size seatposts, but this seems to be a funny size. Will a one-and-three-eights derailleur clamp fit? Will I need a shim? Thanks!

sydney
08-08-05, 05:54 PM
I just put the calipers to my Easton aluminum-frame seat post (measuring for a front derailleur). I measure 1.28" (!). I've heard of one-and-a-quarter and one-and-three-eights size seatposts, but this seems to be a funny size. Will a one-and-three-eights derailleur clamp fit? Will I need a shim? Thanks!Word on the street,is that you measure seattube diameter to get derailer clamp diameter. ;)
FarHorizon
08-08-05, 06:03 PM
Word on the street,is that you measure seattube diameter to get derailer clamp diameter. ;)

Darn! I learn something new every day.. Ain't it great? :D Thanks!

moxfyre
08-08-05, 06:07 PM
Word on the street,is that you measure seattube diameter to get derailer clamp diameter. ;)
Barnyard waste! It depends what color it is :p





Sydney is, of course, correct. You need to measure the seat tube, not the seat post. If your seat POST measures 1.28", then chances are your seat TUBE measures 1.375", since that's the only common size which is LARGER than 1.28"... but you oughta measure it yourself to be sure.
FarHorizon
08-08-05, 06:11 PM
Sydney is, of course, correct. You need to measure the seat tube, not the seat post..

Sydney's usually correct - My original post was wrong. I measured the seat TUBE OD, not the seat post as originally stated. The OD of the tube is 1.28". That's why I posted in the first place. My bad. So, let's try it again - is 1.28" any kind of common seat post diameter?
moxfyre
08-08-05, 06:23 PM
Sydney's usually correct - My original post was wrong. I measured the seat TUBE OD, not the seat post as originally stated. The OD of the tube is 1.28". That's why I posted in the first place. My bad. So, let's try it again - is 1.28" any kind of common seat post diameter?
Okay, I'm confused by this post again :) You actually measured your seat TUBE to be 1.28", and now you're asking if that SAME MEASUREMENT is a common seat POST size?

Seat POST diameters are usually done in metric, so 1.28" is 32.512 mm. That's pretty big, I haven't seen a seat post bigger than 32 mm, but I'll bet sydney has :p

You may want to check out Sheldon Brown's seatpost database: http://sheldonbrown.com/seatpost-sizes.html
FarHorizon
08-08-05, 06:27 PM
Apologies to all: I've bolluxed up this thread from the start - I'm brain-dead this evening, obviously..

The seat tube measures 32mm OD (1.25"). I need a 32mm or 1.25" derailleur clamp. This wasn't difficult at all - I just made it that way.

Excuse the brain fart :o
dafydd
08-08-05, 06:27 PM
Okay, I'm confused by this post again :) You actually measured your seat TUBE to be 1.28", and now you're asking if that SAME MEASUREMENT is a common seat POST size?
http://sheldonbrown.com/seatpost-sizes.html

confused as well, but FWIW, QBP lists a 32.4 and a 32.6, neither of which i would guess are very common.