Rooney 

I just got a Campagnolo Record Ti seatpost, which I've measured with calipers at 27.2 (were they made in any other sizes?), that I want to put in my CAAD 5 frame which is also 27.2. The alloy seatpost that came out of the CAAD presented no problems and the seat tube appears clean and clear, but I have to wrestle with the Ti Campy post to get it to go in. I'm using grease and there's no marring, but it's a real struggle. I pulled the Ti post out because I don't want to find out that it's stuck in there later.

Is this a common experience for these posts? Would it be advisable to lightly sand the seat post, or does Ti not react well to that?

grumpus

I'd try thoroughly cleaning out the seat tube before resorting to modifications - attach string to a rag, soak it in solvent, jam it in with a stick and pull it out again, repeat until no more dirt and dried grease comes out. (Probably best to do this with the frame inverted to protect the bottom bracket.) Then try fitting the seatpost with no grease so you can get a feel for where a tight spot may be - if you look inside with a flashlight you may be able to see where it's rubbing, in which case it might be good to ream the seat tube a little, but only if you're sure the seatpost isn't oversized.

Kontact

What does the old seat post measure?

bboy314

Running a drill with a flex hone in the seat tube couldn’t hurt, in addition to the cleaning procedure above. Have you verified that the old post is definitely 27.2?

JohnDThompson 

There can be size variations in manufacturing both frame tubing and components; perhaps your seat tube is on the small side of acceptable inside diameter, while the post on the large side of acceptable outside diameter. In any case, @bboy314's suggestion to verify that the original post is nominally 27.2mm, and if so, run a flex hone down the seat tube is good. Just go easy and check fit frequently. You don't want to remove more material than what is absolutely necessary.

FBinNY 

Let's start with an understanding if tolerance. NOTHING is exact, so we have to define an allowable range. Since you can't put a big peg in a small hole, we draw a line. The post has to be on size or up to 0.05mm smaller, and the tube on size or up to 0.05mm larger. That means that we can have dits that vary from zero clearance, aka super tight, to up to 0.1mm sloppy.

From your OP, I'll assume your tube is close to minimum, and the post near the max. That may be compounded by some ovalness of the post, or top of the seat tube.

I'd start by gently flexing the tube open and seeing how the fit is further down. If it's OK, then I'd live with it. If it b is tight further down, you need to ream the tube to a hair larger, ie. 27.25.

Kontact

Instead of assuming, the OP could measure his old post before modifying the frame, since he clearly has a caliper.


Once the OP has established that his old post was in the 27.2 ballpark (instead of a 27.0 with a tweaked opening to the frame), then he can consider reaming. But not until he tries the simple solution of spreading the clamping ears slightly.

Being a Cannondale, don't assume the penny trick is going to work.

FBinNY 

I give credit to the OP regarding the correct size being 27.2 for a few reasons.

1- he likely read the size off the original post, or possibly took a moment to measure.
2- IIRC Cannondale never made 27.0 frames, though that's no gauranty
3- the OP described a snug fit, not a no fit, so something smaller than 27.15 or so is ruled out.

In any case, doing the top of tube flex test will tell him what he needs to know.

Kontact

Cannondale never made a 27.0 bike, but if an undersized post made it into the frame, the result is not going to be solved by reaming. So it is far better to know what happened by checking the old post instead of assuming.

FBinNY 

I know you love to argue, or pretend to be the most knowledgeable person here. But instead of nitpicking other peoples posts, you might better serve the community by prioritizing posting your opinion over critiquing others.

So, I've posted my suggestions, responded to your BS, and am now done, until/unless the OP asks more help.

Have a nice day.

Kontact

You're rude and frequently wrong.

Get those three beers in the mail yet?

soyabean

There's always nominal and actual.

My experience in this recent thread may help you.

https://www.bikeforums.net/classic-v...post-size.html

Rooney 

The original post is now on a bike I built for a friend, a CAAD 8 which is also 27.2. I have the carbon 27.2 seatpost from my Topstone which I just tried in the CAAD 5 frame, that went in without trouble. There aren't any noticeable obstructions or obvious areas in the seat tube that would affect the fit of a seat post, but I'll give it a thorough cleaning to see if that makes any difference.

soyabean

Like I said: nominal 27.2 does not imply actually 27.20mm .

Having a 27.25-27.30mm will cause your issue.

Some posts are made more smaller or bigger than others.

Kontact

At this point you can choose to hone the seat tube to accommodate this post, or decide that the frame works very well with most other posts and move on from the Ti one. You may get to a point where it goes in smooth without requiring too much tightening for other posts, or you may not care.

I have a Litespeed that requires a tire iron in the binder ears to move the Kingsberry post up and down, but that's all it takes. You can try that as well.

Crankycrank

Be careful if you decide to use a flex hone on aluminum as it removes the alu rapidly, alot faster than a much harder steel tube.