Seat post question...

[cannedheat]

Ok, this quaestion may sound daft but here it goes...

The website for my new Specialized Hardrock Sport states that the seat post is of 27.2mm in diameter yet the actual post on my bike has 30.(?)mm stamped on it...

Is the 27.2mm actually an internal diameter or is there just a mix up somewhere?

Thanks

[mrandy]

27.2 is external and the most common size

[rico]

Yeah, just measure the diameter of the seatpost across the bottom. Should be easy to see if its 27.2 or 30something.

Sure it isn't the length of the seatpost, as 300mm is a common length?

[cannedheat]

Na, not the length, it's defo something like 30.9 with the 'Ø' symbol. Don't think I actually 'need' a new seat post, after all the bike is less than a week old, but some of the carbon USE or alloy Thomson ones look soooo cool.

I actually need a new stem more than a seat post as the current one is a touch too short...

[Selmer]

Yeah, it's a fat one on Spesh. 30.9mm is correct. There are a few odd sizes kicking around now; long gone are the days of an industry standard 27.2.

[jamesvw]

Yeah it's a 30.9 seatpost on my spesh bighit. really limits your choice of seatpost. tip my local bike shop gave me was, they gave me a 30.9 shim in the seat tube, making it a new diameter of 27.2, then i could choose from a better range! i went for an fsa one, its the same clamp design as thompson seatposts (that cost about 60 quid), mine was 15!!! much stronger, as i kept snapping single bolts

[chrisjl]

jamesvw said:

..they gave me a 30.9 shim in the seat tube, making it a new diameter of 27.2, then i could choose from a better range!

And is the bottom end of the seat tube shimmed too? Otherwise you're asking a lot of the top 2" (or however long the shim is) of your seat tube, which now has to deal with a whole lot of leverage.

[jamesvw]

the shim goes in at the top, and goes down the seat tube, it only leaves about half an inch 'un shimmed' so leverage isn't that bad. the guys at the shop know the kind of rdiding i do (DH) so if there were any concerns they wouldn't have suggested it. ive been using it now for about 12 months, had a good few hard crashes, and no problems. only drawback really is that the shim covers the little hole in the seat tube thats used to tell u where to set the max seat height!

[orgasmicliving!!]

shouldn't be too hard to get a machine shop/fairly adept mechanical-type person to make a channel in the shim so you can still use the sighting hole in your seat tube?

[moleamol]

orgasmicliving!! said:

shouldn't be too hard to get a machine shop/fairly adept mechanical-type person to make a channel in the shim so you can still use the sighting hole in your seat tube?

Shouldn't need it with a decent shim. These are made by a company called 'Problem Solvers'.

[jamesvw]

actually, i think mine has a bit cut like that, must check! if so, shows i don't think things through! ive been struggling measuring gaps with my finger all this time...lol. cheers orgasmicliving!