I'm going to be cutting my fork to fit my 55CM frame, but I want to also be able to slap it onto a 56CM if need be later on. I went with this route on my mountain bike; I left 3.5CM on the steerer (used carbon spacers to make it look sexy), and the fork fits several other frames well. But I'm wondering what the average steerer sizes are for 56CM road frames.

Cheers!

Oh - I'm completely cool with you guys just telling me what you cut your steerer to and frame size.

Knowing how long others cut their steerers will do you no good since you don't know if they have their bar height set the same as you want.

You need the headtube length and the stack height of the headset you plan to use. Then add the height of any spacers you want and the stem's clamp width to calculate the total steerer length.

Here is some data to get you started: My 56 cm Co-Motion has a headtube length of 135 mm and my 57 cm Litespeed has a headtube length of 150 mm. both bikes use conventional headsets, not integrated.

Leave more than you think you need until you can confirm with an actual fit. Just in case I would set up what you need to for this frame with two or even three 10 mm spacers above the stem on your 55cm setup to allow for possible issues on the next frame. Once you know exactly what the maximum needed is through an actual fitting then you can trim off the excess on the largest fit.