Why would you say that? In the stratified fluid case, the air can be treated as inviscid. Or are you thinking about problems from breathing underwater?

Alright, simply; moving at the speed of surrounding fluid, no wake; moving faster than surrounding fluid, trailing wake; moving slower than surrounding fluid, leading wake. It is exceedingly rare for a cyclist to be moving slower than the local (1-2 m above ground level) wind. It's happened to me exactly twice in twenty-five years of riding.