I usually change my boots for my lightweight cheap trainers for road walking, it's not only sole wear that's my problem, but road walking also seems to make my feet too hot as well. Its that part of hiking which I dislike. It's always a personal judgement though, based on me looking at my map and then usually getting into a 'shall I, shan't' I thinking loop. I usually make the decision based on how long the road walk might be, so, for example, I did it twice on the Two Moors Way.