Bicycle Mechanics - How unlikely is it that a 27.2mm seatpost will fit in a bike that has a 27mm seatpost

at the moment?


Totally skint and I need a new seatpost. There seems to be a decent 27.2mm one in a sale, but it appears that according to my bike's spec online somewhere it currently has a 27.2 mm diameter seatpost. Should I just forget it and pay the extra or is .2 of a mm not much and it might fit anyway?

Cheers

you can take some sand paper to the seatpost and shave off that extra 0.2mm in no time.

wear a mask, aluminum dust is toxic if inhaled

you can take some sand paper to the seatpost and shave off that extra 0.2mm in no time.

wear a mask, aluminum dust is toxic if inhaled

of course, then you have to factor in how much the sand-paper and mask cost. Not to mention your time

get a 27.0mm - they're cheap enough. I don't think it's worth mucking around with sandpaper unless you have a seatpost that's a weird size and hard-to-find, or very expensive. Or if you wanted to fit a suspension seatpost (probably only available in really common sizes) into a less-common-sized seat tube.

I happen to have two sitting around (one road-length from the 80's, one mtb-length from the late 90's) if you want one of mine. Probably no more - and maybe less - than buying a new 27.2 on sale, whether you buy a used 27.0 from me or someone else.

How unlikely is it that a 27.2mm seatpost will fit in a bike that has a 27mm seatpost

I'd say about 99% unlikely, unless you modify it as mentioned above. If you already have mismatched brakepads and popcan-shims holding your stem and bars in, or you have three different colours of rusty cable housing and both your tires have multiple duct tape repairs (in short: if the bike is a total beater), then go for it

Many seatposts are available in smaller sizes - like 25.4 - and you can use a shim to make them fit properly. And 25.4 seatposts can be very very very cheap - that size is regularily used on some of the cheapest bikes around. But even a reasonable quality aluminum seatpost from a shop in the correct size is going to be less than $20. A used bike shop or co-op might have something very cheap.

Unless you shave the post (0.2mm takes longer than you think unless you have a lathe), which probably won't be very uniform, it's never going to fit. If you get it in without modification, you'll probably seize the post in the frame. Last time I needed a post in an odd size I asked my local shop to order the cheapest aluminum post they could find (likely Kalloy or such). It cost me ~$12, and while it's a bit heavy, it turns out it isn't slowing me down any.

If you're sure that 27.0 is the correct size, there's no way the 27.2 will fit.

BTW- I have a few new old stock 27.0 posts of various qualities in stock. If you're interested, PM me with your target price range and I'll make you an offer.

I've ground down a seatpost 0.2mm and it takes a LONG TIME-LOTTA WORK WITH A HAND HELD MECHANICAL SANDER. I think it took about 1 hour of grind, test, grind test etc, and it looked cheesy at the end. It was a long-maybe 350mm-seatpost, but I probably just did about 7"-175mm- of it.

Pay the extra $$
Charlie

Forcing in a larger seat post is a dumb idea. Seat posts are cheap.

get a 27.0mm - they're cheap enough.

+1

Standard AL post will be about $10-$15.

Haha, I started a thread about this very issue a few years ago. My solution: use a lathe to machine off .2mm from the OD. Problem solved :D

.2mm is only about .008", or the thickness of two sheets of printer paper.