27.2 mm seatpost in 27.0 mm tube?
 

I got a 27.2 mm NCX suspension seatpost for Christmas. The thing is, I just discovered that my 1990s Specialized Sirrus has a 27.0mm seatpost. Is there any way it can fit? It doesn't seem to want to go in, and I'm hesitant to force it. Too bad, as I was looking forward to trying out this seatpost.

You could carefully ream the seat tube to accept the new 27.2mm post, but the cost is likely to be a significant fraction of what it would cost to simply buy the right size post.

I was kind of set on the suspension seatpost idea, though. Well...may just end up selling the bike. Looking for a more comfortable ride.

A few points- Have you actually tired the new post in the frame? Frame IDs and post ODs are not as precise as stated dimensions might make one assume. I would certainly not force a post in tube at all. I would be very hesitant to ream the tube to fit the post without knowing much more about the dimensions and actual tube used. Since the tube has likely suffered some heat distortion there's a good chance you'd be taking off more then .1mm in some spots. Too little wall thickness can lead to greater chance for cracks later. There are many suspension posts made in a 25.4 diameter. One of these with a properly chosen shim could fit with no frame mods. Andy.

A Kalloy seat post is very Low cost and is made in all diameters ... including 27.0mm


I used an adjustable reamer * and carefully shaved out the 0.1mm of wall thickness ,
in the 27.0 RB 1 I had owned since New.

* I used Cutting oil and only expanding the reamer a few thousandths at a Time ..
... until the post I had In Hand, Just Fit.



Of Course I cannot See the Bike You are speaking of..

FWIW UK USE had suspension seat posts in 25.0mm I had a AlAn with a 25.0 seat post ,
I used their sizing shim with a 25>27mm shim sleeve, initially ...

25.4 to all sorts of out side diameters in 0.2mm increments.. are made ..

I have 2 bikes with Oversize seat tubes and seat post shim sleeves .

so Yes get a 1" suspension seat post and then a sizing sleeve to get it to Fit.

If you have a caliper/mic, measure the new post in multiple directions and make sure it's round.
Most likely it is, but there's an outside chance......

Bought a bike for parts last Fall. Previous owner force fit a 27.2 post into a 27.0 ST. It sort of worked, but was a bear to get out without a lot of scratching. There is a range of tolerance so some fits will be impossible and some just may work. I would recommend against it, though.

You could fit wider tires or, even better, get an old MTB and fit some real wide tires.

Look at all that room.

http://bikeforums.net/attachment.php...hmentid=500496

Here's a 2.3 on my old Bridgestone.

http://bikeforums.net/attachment.php...hmentid=500497