Seatpost sizing

[tron]

Hello,

I posted this question in another thread, but it hasn’t been answered, so I’ll post it with a more appropriate topic.

I just got a new unicycle…
The good news, I won’t even need to use a seatpost clamp on the old 20incher. That’s also the bad news. The new one happens to be 22.2mm. The old one is 22mm. So the old one slips into the new frame rather easily, while putting the new post into the old frame took some WD40 and a lot of twisting and pushing and marring my legs. I’m not too worried about the old uni and damage that may be done by having an oversized seatpost (though I may take it out to put some more durable grease in there), but I am worried about having an undersized seatpost on the new uni frame… especially since it’s going to be ridden a little more roughly. There really isn’t much play between the post and frame… you slide it in and when you rock it back and forth it moves maybe half a millimeter… just enough to hear a click. Is there a danger with this? I do happen to have two semcycle seat post clamps if that would make a difference. It is the Sem XLW 26" frame. Thanks for any input.

[sendhair]

Tron, you may have seen this already, but just in case, from the “Seat post to seat post tube measurement” thread:

originally posted by john_childs:

The seatpost diameter should be the same as the ID of the seat tube. A 0.1 mm difference is a big difference as far as seatposts go. /snip\ When putting in a seatpost do not force it in the seat tube. If you have to force it, it is not the right size and will possibly get stuck. It should be a snug fit, but you shouldn’t have to force it. You should also grease the seatpost and/or the inside of the seat tube so the post doesn’t get stuck in the seat tube due to oxidation (see <http://www.sheldonbrown.com/stuck_seatposts.html&gt; for the reasons why you should grease a seatpost).

I think 0.5mm is too much play to be safe. You probably should shim it.

Also, WD40 is penetrating oil. You should really use grease.

Hope this helps…

[sendhair]

On the other hand, there’s this tip from Sheldon Brown:

Today’s helpful hint: save weight and prevent theft:
Secure your seatpost with epoxy cement and throw away that heavy binder bolt…let’s face it, you aren’t going to grow any taller, you don’t need adjustability!