I have bought an FSA carbon seatpost and need to reduce the length so that it sensibly fits inside my traditional Reynolds 531 Longstaff touring frame – no sloping top tube so only a few inches protrudes from the seat-tube.

Can I simply take a hacksaw to it? Is it as simple to cut as a steel/aluminium one?

Yep, just the same, get a nice cut with a blade with lots of teeth. 32tpi would be good, but anything will cut it.

If you keep rotating the post after every couple of strokes you will get a smoother cut, and no fibres hanging out the end. And it’s less likely to go all wonky.

I wouldn’t reccomend it.

I never tried it myself but I’m an aerospace engineer specialising in composites. There’s a chance you cause delamination between the lamina, if these delamination grow you could dramitically reduce the strength of the post.

If you are still going to do it anyway, i’d wrap a few layers of gaffer tape around the post where you intend to cut it. This should help keep the fibres in place on the outside. Perhaps shove an old broom handle or similar up the middle to try and restrain the inner fibres in the same way.

Also make sure you where a dust mask. Small carbon fragments can do nasty things to you lungs!

I cut through a carbon steerer tube with the help of a cutting guide.

Wrapping tape round it, which you then cut through, could be useful.

I don’t think there is much danger of causing delamination. There is plenty of filler in seatposts and steerer tubes between the fibres. I bought the hacksaw blade with the highest TPI in my local hardware shop, which should also help. And there was very little dust, which didn’t get suspended in the air. It is not like using a power tool.

I finished by smoothing the cut end with some emery paper.

Plucked up the courage and went for it.

Absolute doddle! Hacksaw went through it like a knife through butter – so much easier than cutting through metalic tubes.

I took care not to press too hard at the end of the cut to ensure a nice clean finish and it looks perfect. Given the ease with which the saw went through the post I can’t imagine any stress issues.

Thanks for all the advice folks 😀

Run some clear nail varnish or the lacquer that comes in car body chip repair kits around the cut end will seal it up and stop and of the outer lacquer lifting.