seat post clamp sizes??

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Buster_05
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Joined: Tue Feb 28, 2012 03:55 am

seat post clamp sizes??

Postby Buster_05 » Thu Mar 08, 2012 14:51 pm

Hi there,

I need to get a new seat post for my langster (2007 model)

The one on there is shoot and threaded, and i swear the seat has dropped a bit since i got the bike yesterday.

Ive realised there are 3 different sizes. where do i take the measurement from?

Or does some one know the correct size i need?

I found some specs on the bike, but the specs say the seat post is 27.2mm, the smallest clamp size ive found on the bay is 28.6mm

http://www.specialized.com/us/en/bc/SBC ... nuItemId=0

Can some one point me in the right direction
Cheers
Jack

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HoHoHoBlueGiant
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Joined: Wed Sep 24, 2008 11:40 am

Re: seat post clamp sizes??

Postby HoHoHoBlueGiant » Thu Mar 08, 2012 16:11 pm

I've just had to get a new one myself. Easiest solution is the simplest, measure the diameter of the old clamp, measuring from inside edge to inside edge.

The differences between the 3 sizes is enough to determine which one's needed. Mine measured roughly 35mm, so 34.9. Or just take the old one to your LBS and compare sizes, you can see quite a large difference when you have them to compare.
Wind. Cold. Rain. Pick two.

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nicklouse
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Re: seat post clamp sizes??

Postby nicklouse » Thu Mar 08, 2012 16:15 pm

The easiest is to measure the circumference and then.....

Have a look in the FAQs in the MTB tech section ;)
"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown

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nicklouse
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Re: seat post clamp sizes??

Postby nicklouse » Thu Mar 08, 2012 16:26 pm

nicklouse wrote:The easiest is to measure the circumference and then.....

Have a look in the FAQs in the MTB tech section ;)

Scrub that the easiest is to look on the underside of the old clamp as in most cases here is a number stamped on it.
"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."

Parktools :?:SheldonBrown

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g00se
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Re: seat post clamp sizes??

Postby g00se » Thu Mar 08, 2012 21:15 pm

27.2mm sounds right, it's a common size - that's the inside diameter of the frame seat tube. However, for the clamp, 28.6mm is the outside diameter of the seat tube that size clamp will fit.

At a guess - as it's the same for me - the outside diameter of your seat tube could well be 31.8mm.

Best use vernier calipers to check. But if you haven't got any, measure the internal and external diameters of the seat tube (with the seat post removed) across the top of the tube at it's widest point.

Buster_05
Posts: 30
Joined: Tue Feb 28, 2012 03:55 am

Re: seat post clamp sizes??

Postby Buster_05 » Fri Mar 09, 2012 12:56 pm

ok so ive got the post out, and the outer diameter is to the nearest mm on my tape measure 31mm.

so a 31.8 off ebay should do the trick, am i right?

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g00se
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Re: seat post clamp sizes??

Postby g00se » Fri Mar 09, 2012 13:58 pm

Sounds good.


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