Don't own one yet but I'm looking at the M925a2. Been doing lots of reading and looking at past and current sales. Among the ever growing list of questions I find myself researching, one finds me scratching my head. Given they have air brakes. So when they sit for a while and loose air pressure the brakes are still on by desing. So why do i see so many pictures of trucks on flat ground with wheel chocks, or logs, rocks, chuncks of steel. Am i missing something with these things. Kinda thought that was the point of an air brake system.