But anyone who "rolls coal" doesn't have a truck set up to always do that. They'll have a switch on their console which makes it happen (or something digital). You don't need to try to not roll coal if you don't want to. Probably what happened is the person just drove a normal truck and knows that diesel fumes are stinky and tried to coast by the bikers so there would be the least amount of exhaust near them.
replyNot necessarily- many blow out black smoke when the throttle is pressed hard, but not when pressed gently. From what I understand there is a way of tuning the ECU to do this. But also there can just be a switch
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