I’m with Mortac on this one. I’ve pretty much always done my hills on a paved surface with no problems. The incline offsets any effect the pavement may have. Pavement insures that you’ll find a flat, even hill with a consistent incline. If you can find such a grass hill great, but pavement is ok.
I’m with Mort too. The best “hill” I ever had was in Louisiana…..where there are no hills. There was a great ramp that led up to the basketball stadium that was evenly surfaced, had a consistent incline, provided great ‘return’, and had enough length for us to do anything I wanted. Also, because it was on the side of a sporting facility, we didn’t have to worry about oncoming traffic.