This is not really a touring question, but I thought i would find more flat bar users here than in the "road riding" section.

I am building up a new road bike for my wife. She never grew to like drop bars, and wants to try a flat bar. That point is for now non-negotiable.

So, my question is: what width to shoot for?

I know that the best answer is "go with what feels right", but I have found (from previous experience on her road, mountain, and commuter bikes) that she is not very good at telling what needs to change in her setup. Just that she is happy or not happy.

So I am curious what a good starting point is? I have several flat bars that I can cut down, so if we end up going too narrow I can just grab another bar from the parts bin.

She rode 40cm (center to center) drop bars and seemed OK with that. her mtb and town bike both have 660mm wide bars, but i don't think that is going to work well for a road bike that she will be doing a lot of miles on.

The narrowest bars I have are 580mm (from my early mtb days in the 90s). I have the 580mm on there right now and even that seems really wide even for me (even though I run 750mm bars on my mtb)

I was thinking of cutting these down to 550mm. Is that a good starting point for this? I'm using ergon grips with the integrated bar ends.

I am just curious what other people's experience is with this.