Is it ok to run a slighly smaller diameter seatpost....?

[daj]

Spooky question ...... I was doing and thinking the same yesterday .... need a 27.2 only got decent 27.0 posts ..... Did pop one in but decided against it and to just put a crappy one in for now until I find the right size.

Coming from a non engineer you just wouldnt think 0.2mm would make that much difference? :?

 

[legrandefromage]

To be fare, on the bottom feeder shite I put out to pay the bills, its whatever post that nearly fits, the new owner wont care. It'll be locked up against the railings in Cambridge somewhere, nicked, sold again and probably end up at the Ramsey police auction.

With decent stuff, I get the Vernier callipers out and measure that sucker!

 

[Anthony]

I wonder whether this isn't a slightly exaggerated response if we're only talking about 0.2mm. My Kilauea is specified for a 27.0, but I find the 27.0 just about loose enough to fall down the tube under gravity, while a 27.2 is a snug fit. So I use a 27.2, but I'm sure the huge majority of owners would use a 27.0 and have no problem.

If you try to bridge too big a gap, the clamp will be distorting the top of the tube and you can get a crack starting from the bottom of the slot. But I personally doubt whether 0.2mm is enough to do that, provided you have plenty of post submerged.

Still preferable to have a snug fit though, I don't deny that.

 

[daj]

Hmmmm well im digging deeper here as looks like my two Zaskars could actually have different sizes anyway !?!? Hence why the 27.0 did actually look very ooooeeeerrrrr because it could be a 26.8 as I took it from the early 1994 frame not the later 1996 frame which would make it 0.4 of a difference :roll:

 

[barry2017]

To be fair, in the early 90s all Dawes Galaxies were sold with 27.0 seatposts, and the 531ST seat tubes were designed for 27.2.
But 531ST is a beefy, thick walled steel tube. I wouldn't want to risk anything finer.

 

[MJN]

As an engineer who regularly works to 0.1mm tolerances I would say shim it,if done properly,like Andy R describes,I can't see there ever being a problem.

 

[clockworkgazz]

no, buy a new post and then buy a new frame for the other post. this is the best way.

Thats the retrobike way "honest honey, this seatpost needed a new bike "

 

[Andy R]

As an engineer who regularly works to 0.1mm tolerances I would say shim it,if done properly,like Andy R describes,I can't see there ever being a problem.

I did it because although the seatpost size was intended to be 27.0mm, the seatpost was loose enough to drop down under its own weight as soon as the clamp was released - which in my book is too loose.
The Coke can works well for shim material as it is soft enough to form a lip at the top - steel shim stock would probably crack if you attempted this.

Brass shim stock would probably be ideal - and if it is to be bonded you can do without the lip anyway.

 

[Russell]

As an engineer who regularly works to 0.1mm tolerances I would say shim it....

LOL, I was just thinking that. I work to +/- .01mm on a lot of the stuff I do (.003mm limit on a job last week!) and talk of "it only being .2mm is making me cry.

As an aside, I'm looking for a nice 27.0 seatpost but can't find one. If you lot have so many... flog me one please!

 

[yellow-heapster]

Hi, - I'm new, just joined today. I have an old Kona Lavadome which I have owned from new (’94 or thereabouts I think, the one with the yellow + splatter paint job). I lost the seat post after about 1 week, leaving it in a layby in France after putting the bike on a car-rack and then driving off without it. I bought a replacement to see me through and its been on the bike ever since. Trouble is its too narrow, I have to do the clamp up real tight to get it to stay put. Can anyone tell me what diameter post I should be using…?