Seatpost Claimed Diameter V's Actual Diameter.

[FRSMark]

I'm told the frame I am restoring requires either a 27.0mm or a 27.2mm seatpost (the previous owner can't remember). However when I pop a 27.0mm post in there it feels loose & sloppy. Conversly, when I pop a bar, turned to exactly 27.2mm dia it is VERY tight.

I was wondering, does a 27.2mm seatpost actually measure 27.2mm, or is it actually slightly under this size?

Perhaps if somebody has a 27.2mm post they would be kind enough to pop a vernier caliper over it to check.

Many thanks

 

[suburbanreuben]

This wouldn't be a Race Face post you're talking about, would it? I find they are extremely tight - on everything except Rocky mountains.

 

[FRSMark]

This wouldn't be a Race Face post you're talking about, would it? I find they are extremely tight - on everything except Rocky mountains.

No, it's an ally bar that I have lying around, that just happens to be 27.2mm dia exactly.

 

[yo-eddy]

Try to find a Thomson post. they tend to be spot on in their sizing

 

[cchris2lou]

if 27.0 feels loose and 27.2 tigh , then it has to be 27.2 you need .

never heard of a 27.1

is the frame nice and clean inside ?

 

[FluffyChicken]

Yes they do measure what they should be .. give or take that particular manufacturers tolerances.
The other problem could be that it was a 27.0 frame and a 27.2 has been use in the frame and so stretching it a little over time.
Clean it out, scrape around and get the dirt ou. Possibly you Q/R clamp is not working well. I find the cam style ( e.g.Tranz-X) where the cam is also the lever need to be tighter (from feel) than say a shimano one where the outer casing is pushing in. But that's just the way they work.

 

[Scrat]

From what i've found most frames are the size quoted and the Post tends to be .002-3" undersize

but in saying that, MTBs aren't exactly renowned for high tolerance engineering :shock:

 

[FRSMark]

Turns out it's a 27.2mm seatpost, even though a 27.00 bar will not fit, a 27.2mm seatpost I tried at Hellfrauds does.

Ordered a lovely FSA carbon wrapped one from CRC for a HUGE discount.