but if your smacked dead-on with a s10 while driving on 2 wheels, I'm not buying it. I don't care how much armor that bike's got, you should end up on the ground.
Err... if a bike gets hit by S10, it's just as dead as a footman. Both are wounded on a 2+ and both are instakilled (unless theyre something nuts, like a warboss or nurgle lord).
S5 is -specifically- only really better against small arms. Anything S7 or higher doesnt care if it has S4 or S5. If a bike gets hit by an autocanon shell, the bike's toughness isnt doing squat. 2+ is 2+.