so anything over 20 miles and 13mph is a challenge to me. My kids don't want to ride for too long, so usually the challenge is more speed than distance. When they are older I look forward to getting in longer rides. Also, because I am limited to trails with my Burley ( I wound't want to take the kids on the road), everything is flat. I'm actually looking forward to hills and I'm sure they will be a big challenge. BTW - I've only been riding for 1 1/2 months, so I'm sure things change with time.