Not to get too hung up in the science, but the two ways the mass of the bike matter are with how much they slow the car down, which I suspect is insignificant, and how the mass of the bike affects braking distance. I think that is offset by the superior braking of a modern motorcycle. The mass to be considered is your body mass. The amount of damage you sustain is a function of the equation e = mv^2. The kinetic energy in the mass of your body is the square of the speed you are traveling at impact. This is eye opening when you consider that 50mph squared is 2500 and 30mph squared is 900 so you have 2.7 times the energy at 50mph. Speed is very much not your friend. It is also worth pointing out that braking distance is also the square of the speed. Around here we have two things deer and idiot drivers. I'm old enough that I heal slowly so I only ride on the track.