Bycycle racers sometimes wear teardrop-shaped helmets that taper away behind their heads. Why does having this

Question

Bicycle racers sometimes wear teardrop-shaped helmets that taper away behind their heads. Why does having this smooth taper behind them reduce the drag forces they experience relative to those they would experience with more ball-shaped helmets?

Answer 1

Airflow around a cylindrical or spherical object creates turbulence on the downstream side of the object. This turbulence creates drag. An airfoil behind the helmut reduces the drag.

It's not a huge effect, but when races are won in tenths of seconds, every little bit helps.
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Answer 2

Less air disturbance. Air collects behind a traditional helmet during motion and creates a disturbance that does not contribute to faster times.