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Seat post diameter for new titanium Audax bike

Old 03-21-14, 06:58 PM
Donnie Jonhson
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Bikes: Many, mostly old, steel, heavy and beautiful + one titanium bike; pretty much the complete opposite of my other bikes.

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Seat post diameter for new titanium Audax bike

Hi Everyone,

I am in the process of building a high end titanium Audax/ultra distance bike. The bike has been assembled and riding perfectly, beyond what I ever expected.

In the process of building the bike I borrowed the 27.2 diameter Ritchie seat post form my mountain bike and installed it with a 27.2-30.9 Crane Creek shim. The frame requires a 30.9 diameter seat post. I did this as a the frame geometry (seat tube angles) are different to my usual bike and I was unsure what set back I would require.

Now that the bike a assembled and being ridden, it is time to purchase a new seat post. I am primarily considering an aluminium seat post however will consider a carbon one.

My questions are;

Should I purchase a 30.9 diameter seat post or continue to use the 27.2-30.9 shim and a 27.2 seat post?
Will there be any noticeable difference between a 27.2 and 30.9 seat post?
Have people experienced any problems with their frame when using a shim and a smaller seat post?

Kind Regards

Donnie Johnson
Donnie Johnson is offline  
Old 03-24-14, 04:23 PM
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I predict the consensus will be that:

1. There is no advantage to your current arrangement, and maybe some mild disadvantages.
2. You need to buy a new seatpost anyway, it doesn't really make sense to buy anything but the right part to put on a high-end bike you just had built.

Of course, it's your bike, so you can do what you want.
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Old 03-25-14, 12:11 PM
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A larger diameter post may be stiffer than your current arrangement.
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