Gravel on pavement is like hitting a maze of marbles.
Debris can always turn up on the road. I read of where a chap hit a wheel/tyre for he was in a bumper to bumper bit to work & eyes were on traffic & not the surface.
Around 3 weeks ago I was on some of my usual roads carved out of the mtns where the forest comes right down to the small ditches of the twisty 2-lane roads.
Sun to my left so shadows, from the trees, on the road. Suddenly the 929 & I took a sort of hike into the air.
Thought I had hit a chunk out of the road, but no the pavement was in good shape. As I walked back to check I begin to not parts of an 18 wheeler's tyre that had blowen & sure enough in the middle of the shadow was a good portion of said tyre.
Turned around & rode home with caution, wondering if I had picked up some parts of the steel --- fortunately not, but still a reminder of what can be on the road.