The passenger will move some during the run....by sliding backward and/or forward depending on rear wheel spin.....his head is right next to the engine so it is easy for him to hear if traction is being broken.
The passenger is in no more danger then the driver or a solo rider.....in fact less.....it is a shorter distance to the ground..........But then as the former World Champion Roadracer Geoff Duke told the Press when they asked him about his new style leathers back in l954 ...."The plan is not to fall off"........................
In regards to the Aero using a passenger in the sidecar.......Yes, it does slow us down (tests show about
8 to 10 miles per hour) but then it would not be a sidecar without a passenger it would just be a "wheel
on a stiiiiiiiiiiick"...