[Not commuting-specific, but oh well. Couldn't figure out where to post, so just put it here.]

I have great difficulty riding no-handed. I used to be able to do so long ago. I'm pretty sure I'm not balance challenged, so I think it's probably the bike that is making it hard. I'm currently riding a largish hybrid, and the bike that was easy was the smallish road bike. I suspect that makes a difference, but I don't know why.

What are the qualities of a bicycle that lend themselves well to no-handed stability? Or does the bike have little to do with it, and it's all in my head.