Braking Systems and Vehicle Dynamics
What this domain tests
Hydraulic braking principles, force multiplication, circuit safety, ABS, weight transfer and stopping distance. Expect simple pressure and force calculations plus fault diagnosis.
Core rules and concepts
- Pascal's law: pressure applied to a confined fluid is transmitted equally. In a simple hydraulic system, pressure = force / area.
- Pedal ratio multiplies driver effort: pedal force × pedal ratio = force at the master cylinder.
- Brake force at a caliper = hydraulic pressure × caliper piston area.
- A split or dual-circuit system gives partial braking if one circuit fails; diagonal split is common.
- Air in the hydraulic system makes the pedal spongy because gas compresses; bleeding removes it.
- Brake fade is loss of friction from heat, not usually a fluid leak.
- ABS modulates pressure to prevent wheel lock; it does not override physics or shorten every stop.
- Stopping distance = reaction distance + braking distance. Weight transfer increases front tyre load during braking.
Worked example
Pedal force 200 N, pedal ratio 4:1, master-cylinder area 500 mm². Force at master cylinder = 800 N. Pressure = 800 / 500 = 1.6 N/mm² (16 bar). A caliper piston area of 2000 mm² gives clamp force = 1.6 × 2000 = 3200 N. Reason: pressure is common; force depends on each piston area.
Traps that cost marks
Using wheel force as pedal force; forgetting the pedal ratio; calling ABS a substitute for tyre grip; not checking brake runout or hose condition; assuming a hard pedal means the fluid is good.