Suspension, Steering and Tyre Management
This domain covers suspension types, shock absorbers, steering systems, tyre construction and markings, wear diagnosis, balancing and TPMS. The exam expects you to link a wear pattern or handling complaint to a specific cause.
Core rules
- Common suspension: MacPherson strut, double wishbone, torsion bar and leaf spring. Shock absorbers control spring oscillation; a leaking or weak damper causes cupping and poor rebound control.
- Steering: rack and pinion, tie rods, ball joints and electric power steering. Check for play, torn boots and correct fluid where hydraulic. After alignment, the steering angle sensor may need recalibration.
- Tyre marking 185/65 R15 88H means 185 mm section width, 65% aspect ratio, radial construction, 15-inch rim, 88 load index and H speed rating. The legal minimum tread depth in India is 1.6 mm.
- Wear patterns: centre wear from overinflation; both edges from underinflation; one edge from camber error; cupping from balance or damping faults; feathered tread from toe error.
- Balance wheels dynamically, rotate tyres per the pattern and reset TPMS after rotation or pressure change.
Worked example
For 185/65 R15, sidewall height = 185 × 0.65 = 120.25 mm. Overall diameter = (15 × 25.4) + (2 × 120.25) = 381 + 240.5 = 621.5 mm. This matters when comparing replacement tyre sizes and speedometer error.
Traps
- Mixing radial and bias-ply tyres on the same axle.
- Overinflating to reduce rolling resistance and causing centre wear.
- Balancing only the front wheels after a rotation.
- Forgetting TPMS relearn after fitting a new sensor.