Should I cut it?
 

I have a 380mm 27.2mm Moots setback post that Erik has finished to match the brushed ti on my Alliance. With the bike he sent a 30.9 to 27.2 shim to make the switch from the 30.9 Moots setback I'm currently running (the 30.9 will be listed in the classifieds in the next week).

The shim is 10cm long, and and at my saddle height there will be approx 12cm of unsupported post below the shim.

Wondering if it would be better for me to cut off approx 10cm of post which would leave me about 2cm of post extending below the shim and give an overall seatpost length of about 270-280mm. Or am I fine leaving the post full length? Since this isn't the WeightWeenies forum I'm not concerned about the weight of a 10cm section of 27.2 ti seatpost:banana:

What would you do? Run the post as is with 12 cm "floating free" within the seat tube below the end of the shim, or cut so there's enough left for adjustments but have more of the post supported.

Then why cut it??

depending on the frame size and such, you could run into the water bottle bosses but it doesn't sound like you had such problem in your test fitting. other than that, there's no reason to cut it. in fact, you may want to leave it full length if possible for resale down the road.
i've used a 30.9 to 27.2 shim in the past and that transition from fat st to post always bothered me. so at least ride it as is for a while if you can.

I cut excess lengths of aluminum posts going directly into steel frames. Don't think I would cut the OP's.

Don’t cut unless hitting water bottle bolts.

Leave it alone. You might use it on another frame with more SP showing.

Thanks to all. I'll give it a go as is.

No one asked, but the rationale for going to 27.2 is for a bit more compliance in the back end. I don't feel uncomfortable, but wanted to give it a go.

My rationale for asking about trimming was in case having that much post floating inside the ST might cause resonance or something funky that I wouldn't have anticipated.

Leave it alone, install it, and go ride your bike.

Why cut it at all?

Shim or not, any seat tube that has a seatpost reinforcement sleeve (ie many frames) will contact the seatpost only for the 100mm or so length of that sleeve. Feel inside the top of your seat tube. Therefore many seatposts often extend further down the seat tube well below the reinforcement sleeve and/or shim. No worries.

Cutting your seatpost will only reduce its future usefulness and market value.

Consistent and helpful advice from all; thanks. Will give it a go as is. No further discussion needed:)