Road Bike, Cycling Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
796 Posts
Discussion Starter · #1 ·
I am looking for some advice/direction on a seatpost. I am doing my first custom build and of course its also a learning process for me.

I need a 27.2 seatpost but I don't know if I need 27.2 x 300 or 350 or 400? Don't know what the differences are in the 300, 350 or 400. I am assuming its a function of how high you can take the seat??
 

·
Every little counts...
Joined
·
3,924 Posts
Correct, measured in millimeters. 250mm are short ones, would work on a traditional frame. The more compact your frame is, you'll need a longer post. The post should be long enough to extend into the frame past the bottom of the seat lug.

Buy a long one and cut it off if you think it is too long. Better too long than too short.
 

·
Registered
Joined
·
796 Posts
Discussion Starter · #3 ·
Spunout said:
Correct, measured in millimeters. 250mm are short ones, would work on a traditional frame. The more compact your frame is, you'll need a longer post. The post should be long enough to extend into the frame past the bottom of the seat lug.

Buy a long one and cut it off if you think it is too long. Better too long than too short.
Okay, thanks. The frame is a 2007 Tarmac Pro 54cm. I'm thinking based on what you have said probably a 27.2 x 350 would work fine?
 

·
Adventure Seeker
Joined
·
5,115 Posts
A 300 or 350 would be fine. What is your inseam?
EDIT: Measuring min insert depth, an average crank length, and the seat tube, a 300 is more than adequate. Unless your inseam is over 33"
 

·
Registered
Joined
·
796 Posts
Discussion Starter · #5 ·
My inseam is just shy of 31. A 300 would do fine then? Thanks again for all the help fellas.
 

·
Registered
Joined
·
832 Posts
A 300mm should do fine.

As regards cutting them shorter, I wouldn't try this with a carbon seatpost.
 

·
eRacer
Joined
·
2,555 Posts
I have heard of folks cutting Carbon Posts with no difficulties or consequences.
Any reason(s) that you are aware of not to cut a Carbon Post?
Thanks.
John
 

·
Registered
Joined
·
1,037 Posts
mikagsd said:
Okay, thanks. The frame is a 2007 Tarmac Pro 54cm. I'm thinking based on what you have said probably a 27.2 x 350 would work fine?
They are a lot of things you need to be aware of to determine the size seat post you need. Seat post length extending above the seat tube, maximum seat post length that will fit inside the seat tube (can't extend below highest water bottle cage bolt), minimum insertion distance for a particular seat post, and setback needed if any. If you have all those dimensions you will be certain to get a post that will fit.
 

·
Registered
Joined
·
10,160 Posts
info...

More important is the type of seat rail clamp and the setback. I would never buy a post without a 2-bolt rocker style clamp for the best angle control. Thomson's rocker style clamp is great, but the setback options are either zero or the ugly bent post with only 16mm of setback. I need 25-32mm of setback to get the saddle where setback far enough.

I've been using the FSA K-force for several years with no problems. The Selcof/ITM rocker style clamp also works well.
 

·
Registered
Joined
·
796 Posts
Discussion Starter · #11 ·
Thanks for the info. I went with an Easton EC70 27.2 x 350 today. It is the carbon post attached to the alloy clamp that is setback a little bit with the 2 bolt clamp. For those who have cut carbon posts before, what is best to cut it with? Have never cut carbon fiber before....
 

·
eRacer
Joined
·
2,555 Posts
I agree.
It is hard to beat the Thomson 2-Bolt Clamp adjustment.
With a 4mm Allen wrench you can easily 'dial-in' your saddle angle, and it will stat put. NICE!
John
 

·
Registered
Joined
·
3,255 Posts
I just bought that post for a new bike I am planning. Very nice finish and just the right amount of setback for me. However, its so light already, why bother with cutting it off to save a few grams? IF you decide you don't like it and want to sell it, much better to have it at the original length.
 

·
Registered
Joined
·
514 Posts
C-40 said:
More important is the type of seat rail clamp and the setback. I would never buy a post without a 2-bolt rocker style clamp for the best angle control. Thomson's rocker style clamp is great, but the setback options are either zero or the ugly bent post with only 16mm of setback. I need 25-32mm of setback to get the saddle where setback far enough.

I've been using the FSA K-force for several years with no problems. The Selcof/ITM rocker style clamp also works well.
How does one predict how much setback he needs? Trial and error with a plumbline and KOPS?
 

·
Registered
Joined
·
514 Posts
With respect to two-bolt seatclamps, these are more reliable in most applications and allow for infinite adjustability of the seat angle. However, the Specialized carbon post with Zertz insert (I'm borrowing one from a friend) and a very high-end Ritchey WCS carbon posts use an even cooler design (see here: http://www.excelsports.com/new.asp?...ingleBolt&vendorCode=RITCHEY&major=1&minor=19) with a single bolt on the side. Works great and easier to adjust. Might not be as secure as a two-bolt, but mine hasn't slipped yet.
 
1 - 15 of 15 Posts
Top