i understand hydraulic brakes, i understand air brakes, but i dont get air over hydraulic. why didnt the manufacturers just go with air brakes, it seems like there are two systems when one would work. also does the air pressure release the brakes like a air system, or does air pressure apply the brakes like a hydraulic system. if the hydraulic system has no fluid would the tires lock up like air or not work like hydraulic. sorry for my ignorance with this issue.