A dust cloud is made even going 20 mph.
You talk big archer, but if a bicyclist ever tries to put a size 12 cleat in my truck door he will be trying to pedal a bike that is halfway up his *****. No, I am not a bully, just a mean sob when it comes to idiotic bikers like yourself.
Yes, the same type of sentiment felt by men that wear size 12 shoes and get nearly killed (not just a minor beat down, KILLED) by an idiot in his pickup that makes him feel tough.
Get out of your truck, the biker gets off his bike and settle it like men, fine, good, thats what the biker wants you to do, because even before the dent in YOUR truck, he's ready to administer the beatdown on you, only most drivers are too CHICKEN SCRATCH to get out. Your tough, I'm tough, everybody's tough on here, ok bring it on, lets see what you got. By the way, you got a dent in your door now. You cannot legally perform assault on someone for damaging your property.
So you really want to KILL a man over a dent in your truck, or impeding your way to the grocery store, or at the very least BEAT him into a COMA so that he doesn't turn you in to the cops afterwards...He's willing to bet the cost of your cosmetic damage on your truck versus the IDIOTIC maneuver you performed that almost killed him to satisfy your deranged sense of humor or roadrage.
I dont know where you live, but here in central nebraska with the pea gravel roads, it takes about 35-40 mph to get a dust cloud. I can hear rocks in the wheel wells, well less than 20 mph. But if you're passing a biker doing 15mph on gravel, you doing 20, I doubt that anyone is going to throw rocks at you unless you are trying to see how close you can get your mirror to the biker's left shoulder.