Seatpost problem
03-26-18 | 08:50 PM
#1
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Seatpost problem
I have a Bottecchia Sprinter where the seat tube diameter measures 26.19...I got a seatpost at 26.2mm but it still doesn't go into the seat tube.
Am i going to have to try a 26.0mm post?
Am i going to have to try a 26.0mm post?
03-26-18 | 09:43 PM
#3
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I suspect you measured the top ID of the seat tube but not the "ID" an inch or two down. There's a lot of potential distortion from heat and such that can change the ID shape and/or internal circumference (note I didn't say diameter). This is why when folks measure the seat post size they often don't end up with a post that fits the entire insertion amount that the post uses.
The best way to size a post is with trial and error, plain and simple. No possibility of error or assumption. The post either fits in and is loose or able to be tightened in place or it won't fit in enough. better shops keep a collection of posts in different sizes for this testing.
Also know that the post's marked size is usually a small amount under the marked size and can also vary from post to post a tad. Once again the proof is in the actual fit. Andy
The best way to size a post is with trial and error, plain and simple. No possibility of error or assumption. The post either fits in and is loose or able to be tightened in place or it won't fit in enough. better shops keep a collection of posts in different sizes for this testing.
Also know that the post's marked size is usually a small amount under the marked size and can also vary from post to post a tad. Once again the proof is in the actual fit. Andy
03-26-18 | 09:44 PM
#4
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03-26-18 | 09:59 PM
#5
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From: Pico Rivera, CA
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The seat tube clamp is able to expand. With the binder bolt removed the ID measures 26.19mm..with the bolt tightened the ID measures 25.97mm.
Sigh...now to get a 26mm seatpost
Sigh...now to get a 26mm seatpost
03-26-18 | 10:23 PM
#6
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Why not just lightly sand down the circumference of a 26.2 post? That is what we French bike weenies do with stems. (22.2 mm to 22.0).
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03-27-18 | 05:51 PM
#8
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thick tube wall fairly cheap Kalloy post?
26.2 inside a 28.6 OD seat tube (quick math) , shows tube wall is 1.2mm thick..
In a shop an adjustable reamer , can shave just enough steel out of the frame to get that seat post to fit perfectly..
I borrowed that tool in my LBS , one winter, so slow season , and took 0.1mm of tube wall out and so made my RB-1,
a 27.0 , take a more common 27.2 seat post..
and the seat tube bore was also much smoother than the rushed job the factory did , to meet production quotas.
....
26.2 inside a 28.6 OD seat tube (quick math) , shows tube wall is 1.2mm thick..
In a shop an adjustable reamer , can shave just enough steel out of the frame to get that seat post to fit perfectly..
I borrowed that tool in my LBS , one winter, so slow season , and took 0.1mm of tube wall out and so made my RB-1,
a 27.0 , take a more common 27.2 seat post..
and the seat tube bore was also much smoother than the rushed job the factory did , to meet production quotas.
....
Stronglight post is fairly thick walled.
I spent about 20 minutes sanding down the post. I wrapped sandpaper around it and in a twisting motion went at it. Little by little it did go from 26.21 down to 25.98 or so. Arms got tired aftet a while so ill take another stab at it later today
03-28-18 | 03:05 PM
#10
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Grease that sucker!
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N = '96 Colnago C40, '04 Wilier Alpe D'Huez, '10 Colnago EPS, '85 Merckx Pro, '89 Merckx Century, '86 Tommasini Professional, '04 Teschner Aero FX Pro, '05 Alan Carbon Cross, '86 De Rosa Professional, '95 Gios Compact Pro, '95 Carrera Zeus, ‘81 Masi Gran Criterium, ‘81 Merckx Pro, ‘89 Cinelli Supercorsa, ‘83 Bianchi Specialissima, ‘VO Randonneur, Ritchey Breakaway Steel, Rivendell Rambouillet, Heron Randonneur, ‘92 Ciöcc Columbus EL
03-28-18 | 08:53 PM
#11
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From: Pico Rivera, CA
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Luckily my LBS had a 25.8 to test out with my frame so I left for a tune up.
Last edited by bfuser10291295; 03-28-18 at 09:10 PM.
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