Tolls for bikes on roof racks in Europe

Seafordblue

I seem to recall reading somewhere that, over a certain vehicle height, tolls in Europe go up considerably. As we normally carry our bikes on the top of our 4x4  (making them slightly higher than our Lunar) we wondered if we would be likely to fall foul
of this extra cost and if we should change our bike rack. Can anyone help? Is there a charge for extra height?