Years ago in Oslo the police and the national broadcaster (NRK) set up and experiment where they would radar the bikers coming down a small bike road incline.

The fastest they clocked were nearly 80kmh. If you go that fast on motorcycle you are expected to wear a massive helmet and suit, yet the person likely did it wearing spandex and a bike helmet (if that).

now that speed was highly unlikely to be maintained, but do not underestimate the kinds of speeds a bicycle can get up to under the proper circumstances.