When pointed downhill, the squealing lard and meat will be pushing with a 15 lb force. Bummer, a normal human could manage less than 5 miles at that rate. Fortunately, slowing down by half while climbing, taking such a climb at 2.5 mph, the gravity and friction tax also drops by half. And every red-blooded bicyclist knows about evil Lord Air Resistance. At walking speeds, air behaves kindly by moving away with little complaint.
Air has mass, but it's relatively small per unit of volume.
The lower a cyclist's velocity the less important air resistance becomes. That's why picket line marchers can slowly stomp around in circles with their wide-flat signs held high and still have enough energy to shout slogans. I don't rightly know. Most likely high. If a big storm blew up, air resistance would suddenly become a viable concern.