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Car Brakes

  1. Jan 23, 2009 #1
    I have a simply question: how much force must be applied to an average car brake in order to fully depress the pedal?
    Also, if you know the answer, do you know where I could substantiate it?
    Thanks for any help you can offer.
     
  2. jcsd
  3. Jan 23, 2009 #2

    mgb_phys

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    It obviously depends on the car, if you just want a rough answer you can measure it.
    Either hook a fishing scale type spring balance under the pedal and then press down (preferably while not in traffic) or remember how much effort you had to push with and then try and push your foot down on a bathroom scale with the same force and see what it reads.
     
  4. Jan 24, 2009 #3

    Ranger Mike

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    assume you have disc bakes on all corners..there is a brake pedal with actuator arm to master cylinder. usually master cylinder has two reservoirs..in old days only one was used..the front cylinder is larger than the rear as the engine weight is on front end. more weight means more braking requirement. stainless steel brake lines 3/16 to 1/8 inch diameter take brake fluid to each wheel caliper ( piston and mounting arrangement.) the brake disc is fitted to the axle and when force is applied to the master cylinder..pressure acts on pistons pushing brake pads to contact the rotating wheels discs..


    typical mechanical advantage of the brake pedal to master cylinder is 3:1 and 6:1 ( non power brake set up) power brake mech. advantage is 8:1
    our formula car has master cylinder bore of .750" with piston area of .442 sq. inch, makes line pressure with 150 pounds force on piston 339 psi
    pedal travel to move pads 0.010 inch .96 inch ( 4 Pot caliper with 1.50" pistons) generating applied force to individual discs = 2396 pounds

    if you are able to completely depress the brake pedal you have problems..you should be able to depress the pedal about 1/2 inch until you get a firm brake pedal..if not, you pads are too worn or you have air in the brake lines and must ' bleed" the brakes..i.e. pump up pedal and hold it until you buddy cracks the bleeder and permits trapped air to escape..
    lot of other stuff I can tell you but let me know is this is sufficient
     
    Last edited: Jan 24, 2009
  5. Jan 24, 2009 #4

    Ranger Mike

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    actual energy required to decelerate a race car
    energy (lb./ft) = 0.0335 x { MPH Max ) squared ( mph min) squared } x gross weight
    1760 lb. car braking from 150 mph to 60 mph would take 1,114,344 lb./ft.
    and there is MUCHO heat...
     
    Last edited: Jan 24, 2009
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