Brakes, Tyres and Wheel Alignment
What this domain tests
This domain examines drum and disc brakes, hydraulic principles, brake fluid, bleeding, pad wear, ABS basics, tyre construction, pressure, tread wear, wheel balance and alignment. Questions often use hydraulic ratios or wear patterns to test reasoning.
Core rules
- Hydraulic pressure is transmitted equally. Force = pressure × area, so a larger caliper piston area multiplies clamp force relative to the master-cylinder area.
- Brake fluid is hygroscopic; absorbed moisture lowers boiling point and causes spongy feel. Use the specified DOT grade and never mix incompatible grades.
- Bleed from the caliper farthest from the master cylinder, keeping the reservoir topped up and the pedal or lever held.
- Tyre pressure is checked cold. Under-inflation increases sidewall flex and heat; over-inflation reduces the contact patch.
- Tread wear indicators show the minimum safe depth; uneven wear points to pressure, alignment or suspension faults.
- Motorcycle wheel alignment mainly means correct axle alignment and chain adjustment; check that the rear wheel runs in line with the front.
Worked example
A master cylinder has a 12 mm bore and the caliper has two 32 mm pistons. Master area = π/4 × 12² = 113 mm². Caliper area = 2 × π/4 × 32² = 1608 mm². Area ratio = 1608 ÷ 113 = 14.2. A 100 N lever force therefore produces about 1420 N of caliper clamp force, before lever mechanical advantage and friction losses.
Traps that cost marks
Mixing DOT 4 and mineral oil; topping up with used fluid; fitting pads without cleaning the caliper; judging tyre pressure when hot; aligning the rear wheel by the swingarm marks alone when the marks are inaccurate.
Key points
- Hydraulic force equals pressure times piston area.
- Brake fluid absorbs moisture and needs periodic replacement.
- Bleed air from the farthest caliper first.
- Check tyre pressure cold.
- Rear-wheel alignment follows axle and chain alignment.