A bicyclist and a parked car have a head-on collision. Which experiences the greater force: the bicyclist, the car or the same?

Both will experience the same force in the opposite direction, For every force there is always an equal opposing force (newton's third law of motion). But to give a more comprehensive analysis to the event. Momentum and acceleration are other two main factors to be considered to fully understand the concept behind.

Acceleration wise, the bike will experience more, in terms of momentum the bike will also feel more change in velocity as the momentum is translated from the car.