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34.9 seattube, what size seatpost?

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34.9 seattube, what size seatpost?

Old 04-07-10, 08:23 AM
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34.9 seattube, what size seatpost?

I'm making my first venture into building a bike less than 30 years old, and I'm not sure what size seatpost I need.

The frame is a Masi Gran Corsa Premio, relatively newer model, and the clamp diameter for the front derailleur is 34.9. Does this mean I need a 31.6 seatpost, a 27.2, or is more info needed?
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Old 04-07-10, 09:29 AM
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You aren't going to be able to tell with the seat tube size. Try a pair of calipers, another seat post you have, or take it to a LBS and have them try.
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Old 04-07-10, 09:35 AM
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Originally Posted by Purp
I'm making my first venture into building a bike less than 30 years old, and I'm not sure what size seatpost I need.

The frame is a Masi Gran Corsa Premio, relatively newer model, and the clamp diameter for the front derailleur is 34.9. Does this mean I need a 31.6 seatpost, a 27.2, or is more info needed?
You need to measure the *inside* diameter of the seat tube, not the outside diameter.
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Old 04-07-10, 10:03 AM
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Originally Posted by JohnDThompson
You need to measure the *inside* diameter of the seat tube, not the outside diameter.
Yeah, I figured. It seemed like a stupid question, but I didn't know if newer American/English/(Taiwanese) bikes had standards about these things.
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Old 04-07-10, 10:06 AM
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31.6
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Old 04-07-10, 10:09 AM
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It's most likely at 31.6 inside diameter. The tubing walls would have to be pretty thick for a 27.2 seatpost.
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Old 04-07-10, 10:24 AM
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Originally Posted by topflightpro
It's most likely at 31.6 inside diameter. The tubing walls would have to be pretty thick for a 27.2 seatpost.
Or it could be tapered.
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Old 04-07-10, 10:30 AM
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I don't think you can tell by the FD. Just get a ruler and measure the diameter.
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Old 04-07-10, 10:53 AM
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another vote for 31.6
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Old 04-07-10, 11:17 AM
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31.6
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Old 04-07-10, 12:45 PM
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34.9 O.D., 31.6 I.D. Pretty standard size.
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