The key is "staying ahead of the pedals". When I can't stay ahead going downhill I scrub off speed. Last summer I jumped in with the race team while riding a fixed gear for a 6-7 mile flat section. We were going 25-26 mph and I was riding 70 gear inches. I was spinning 120-130 rpm and it wasn't the cranks moving my legs over for me. I had as much pressure on the pedals I could put out. If I had planed to do this I would have had my 80 gi clog on.