I'll be fitting a threadless headset so will I guess I'll need to chop the steerer off at the correct height - that bit would give me the fear.
Don't cut the steerer !
Buy a bunch of cheap spacers (free even if you beg at your local bike shop).
Put these extra spacers over the extra steerer that sticks out of the top of your stem and tighten up as normal.
When you have ridden around and are happy with the height, you can then chop down the steerer to 2-3mm below the top of the stem.
If you are not happy and want to move the stem up - move some of the spacers from above the stem to below - then ride and check - then chop.
Don't cut the steerer !
Buy a bunch of cheap spacers (free even if you beg at your local bike shop).
Put these extra spacers over the extra steerer that sticks out of the top of your stem and tighten up as normal.
When you have ridden around and are happy with the height, you can then chop down the steerer to 2-3mm below the top of the stem.
If you are not happy and want to move the stem up - move some of the spacers from above the stem to below - then ride and check - then chop.
Hope that all makes sense.