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Old 10-17-11, 04:17 PM   #1
DGonzalez
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What size seat clamp/collar do I need?

Hi,
I am trying to find a seat clamp/collar for my old Gary Fisher Montare bike. The seatpost is 27.2mm x 350 mm. What size seat clamp do I need? I would like a quick release one.

Thanks.
David
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Old 10-17-11, 04:37 PM   #2
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The clamp is sized according to the outside diameter of the seat tube. There are 3 standard sizes 28.6mm, 31.8mm, and 34.9mm. Aluminum frames that accept a 27.2mm seatpost will generally use a 31.8mm clamp.
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Old 10-17-11, 05:47 PM   #3
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Quote:
Originally Posted by Bezalel View Post
The clamp is sized according to the outside diameter of the seat tube. There are 3 standard sizes 28.6mm, 31.8mm, and 34.9mm. Aluminum frames that accept a 27.2mm seatpost will generally use a 31.8mm clamp.
There is also a 30.0 mm clamp and it's used on several bikes, particularly on Surly frames.
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Old 10-17-11, 05:50 PM   #4
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With the seat post out, you can measure the OD of the seat tube ..

FWIW, tubes used in most bikes are fractional 1-1/8, 1-1/4, 1-3/8"..
the numbers, 28.6mm, 31.8mm, and 34.9mm are the metric equivalents.

then a manufacturer maybe, shims inside the seat tube ID
to use the common seat post sizes.
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Old 10-17-11, 07:38 PM   #5
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Quote:
Originally Posted by DGonzalez View Post
Hi,
I am trying to find a seat clamp/collar for my old Gary Fisher Montare bike. The seatpost is 27.2mm x 350 mm. What size seat clamp do I need? I would like a quick release one.

Thanks.
David
Take a piece of string or strip of paper, wrap it around your seat-tube precisely, take that string and measure its length in mm, then divide by the number pi. That is the seatpost clamp size you need.
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Old 10-17-11, 07:49 PM   #6
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That is what I thought. So I bought a 31.8mm clamp and it was too small.
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