Replacing seat post - trying to determine diameter from engravings, need guidance
02-01-11 | 02:37 AM
#1
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Replacing seat post - trying to determine diameter from engravings, need guidance
I need to replace the seat post of an older bike that I'm restoring.
The seat post has engraved markings, in which one of the lines of text implies the diameter measurement. It starts with an 0, O or circle but with an angled line through the 0,O or circle. Then it reads 25 and then there is a space, then it reads 40.
My assumption is that this is a 25.4 mm post, and when I measure with a ruler it looks to be true (very close to 1"). Unfortunately I don't have a caliper tool to verify this.
I would appreciate some feedback regarding my assumptions.
Thanks
The seat post has engraved markings, in which one of the lines of text implies the diameter measurement. It starts with an 0, O or circle but with an angled line through the 0,O or circle. Then it reads 25 and then there is a space, then it reads 40.
My assumption is that this is a 25.4 mm post, and when I measure with a ruler it looks to be true (very close to 1"). Unfortunately I don't have a caliper tool to verify this.
I would appreciate some feedback regarding my assumptions.
Thanks
02-01-11 | 04:48 AM
#6
cab horn
Joined: Jun 2004
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From: Toronto
Bikes: 1987 Bianchi Campione
02-01-11 | 08:05 AM
#7
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From: Charlotte, NC
25.4 seams a bit small for a mountain post... I sold Schwinns in the 80's and 90's and all of the mountain posts were in the 26mm -27.2mm range.
I haven't kept up with them since they became a department store bike... could very well be they've made some changes to lower the pricing.
I'd recomend measuring the seatpost tube opposed to the seat post... especially if the bike was not yours originally. You'd be suprised how many people replace seat post with the wrong size. A local bike shop should have a seat post diameter gauge they can drop into the frame for you... that is if your willing to take the bike to them.
I haven't kept up with them since they became a department store bike... could very well be they've made some changes to lower the pricing.
I'd recomend measuring the seatpost tube opposed to the seat post... especially if the bike was not yours originally. You'd be suprised how many people replace seat post with the wrong size. A local bike shop should have a seat post diameter gauge they can drop into the frame for you... that is if your willing to take the bike to them.
02-01-11 | 08:12 AM
#8
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From: St Peters, Missouri
Bikes: Catrike 559 I own some others but they don't get ridden very much.
Use a piece of paper and your mm scale to measure the circumference. Divide by pi and there's your answer. That'll be more precise than you can get measuring the diameter with a linear scale.
02-01-11 | 08:44 AM
#9
Biking Viking.
Joined: Nov 2007
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From: Camp Hill, PA
Bikes: '01 Lemond Buenos Aires, '11 Specialized Stumpjumper FSR, 70s Austro Daimler Inter 10, 80s Motobecane Mirage 10 Fixed Gear
I take a cheap drawing compass and open it till I can just fit it around the seatpost. Then I just place the drawing compass on a ruler. Its pretty darn precise.
But, yeah, 25.4 sounds reasonable.
But, yeah, 25.4 sounds reasonable.
02-01-11 | 11:58 AM
#10
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From: NW,Oregon Coast
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25.4, aka 1" is also made in a chrome-moly steel , I have one left over from single speed build
using a Schwinn Mesa Runner, it, post, came thru a 'red line' dealer ,
SBS Seattle bike, distributor it is strong ..
I had a foot of post out of the frame.
thicker wall seat tube = smaller ID and seat post.
using a Schwinn Mesa Runner, it, post, came thru a 'red line' dealer ,
SBS Seattle bike, distributor it is strong ..
I had a foot of post out of the frame.
thicker wall seat tube = smaller ID and seat post.
Last edited by fietsbob; 02-01-11 at 12:42 PM.
02-01-11 | 12:07 PM
#11
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From: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Wind a dollar bill twice around the post on a very shallow spiral. Draw a straight line across the layers. Unwind and measure from the first mark to the third (about 6-1/2") with a mm scale, divide by 6.28 (twice Pi) and there's your diameter.
Use that as a cross check, but if it says ø25.4 it's 25.4mm, since there's no size with similar looking digits. (it's easy to misread a 28.6 for 28.8 with faint markings, but that kind of error isn't possible with s 25.4)
Use that as a cross check, but if it says ø25.4 it's 25.4mm, since there's no size with similar looking digits. (it's easy to misread a 28.6 for 28.8 with faint markings, but that kind of error isn't possible with s 25.4)
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FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 02-01-11 at 12:41 PM.
02-01-11 | 12:36 PM
#12
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Bikes: 1986 Alan Record Carbonio, 1985 Vitus Plus Carbone 7, 1984 Peugeot PSV, 1972 Line Seeker, 1986(est.) Medici Aerodynamic (Project), 1985(est.) Peugeot PY10FC
I need to replace the seat post of an older bike that I'm restoring.
The seat post has engraved markings, in which one of the lines of text implies the diameter measurement. It starts with an 0, O or circle but with an angled line through the 0,O or circle. Then it reads 25 and then there is a space, then it reads 40.
My assumption is that this is a 25.4 mm post, and when I measure with a ruler it looks to be true (very close to 1"). Unfortunately I don't have a caliper tool to verify this.
I would appreciate some feedback regarding my assumptions.
Thanks
The seat post has engraved markings, in which one of the lines of text implies the diameter measurement. It starts with an 0, O or circle but with an angled line through the 0,O or circle. Then it reads 25 and then there is a space, then it reads 40.
My assumption is that this is a 25.4 mm post, and when I measure with a ruler it looks to be true (very close to 1"). Unfortunately I don't have a caliper tool to verify this.
I would appreciate some feedback regarding my assumptions.
Thanks
Chombi
02-01-11 | 02:03 PM
#13
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You can get a simple caliper at Sears for $8. You'd use it for many other jobs as well.
I also have one of those Schwinns; the components are better than dept store, but not top quality. I like it for bumming around a bit. Seatpost size on mine is 25.4.
I also have one of those Schwinns; the components are better than dept store, but not top quality. I like it for bumming around a bit. Seatpost size on mine is 25.4.
02-01-11 | 02:37 PM
#14
Thrifty Bill
Joined: Jan 2008
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From: Mans of NC & SW UT Desert
Bikes: 86 Katakura Silk, 87 Prologue X2, 88 Cimarron LE, 1975 Sekai 4000 Professional, 73 Paramount, plus more
+1 Either buy an inexpensive caliper (Harbor Freight has a digital one for $10), or take it to a shop. Sizing via the internet is prone to error.
