Chassis Layout and Frames Questions and Answers

Answer: C

The shell is clamped to a bench that holds the undamaged datum points and hydraulic towers pull the deformed structure back to its measured position. Measurement continues throughout the process. Heating modern high strength steels destroys their properties and is prohibited on many members, which is why sectioning and replacement is often specified instead. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: D

The martensitic structure produced by hot forming and quenching is destroyed by any subsequent heating, and the material has too little ductility to be straightened cold. Manufacturers therefore specify complete replacement of such members at defined sectioning points. Repairing them incorrectly leaves a structure that will not perform as designed in a subsequent collision. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: A

Aluminium is difficult to spot weld because of its oxide layer and high thermal conductivity, so self piercing rivets and structural adhesive are used instead, often in combination. The adhesive also seals the joint against corrosion. Repair requires specialist equipment and a separate clean area to avoid contaminating aluminium with steel particles.

Answer: B

Aluminium is anodic to steel, so in the presence of an electrolyte it corrodes preferentially and rapidly at the joint. Isolation using adhesive, coatings or non conducting washers is therefore essential wherever the two metals meet. Mixed material construction has made this a significant design consideration in modern vehicles.

Answer: C

Modern shells use galvanised steel, are dipped and electrocoated so that the primer reaches every cavity, and are then sealed and wax injected. The multilayer system is why bodies now last far longer than those of the nineteen seventies. Galvanising a completed shell is impractical because of the temperature involved and the difficulty of draining.

Answer: D

Cavities collect moisture and are impossible to inspect, so a wax that creeps into seams and displaces water is injected through access holes during manufacture. Underseal protects the exposed underside and is a complementary rather than an alternative measure. Sacrificial anodes are used on ships and buried pipelines rather than on vehicles.

Answer: A

Sprung mass is everything supported by the springs, principally the body, engine, occupants and payload, while unsprung mass is everything below the springs and moving with the wheel. The ratio between them governs ride quality, because a large unsprung mass follows road irregularities poorly and transmits more disturbance into the body. Reducing unsprung mass is therefore one of the most effective ways of improving both ride and roadholding, which is why aluminium and composite components are used there despite their cost.

Answer: B

A light wheel assembly accelerates more readily over a bump and returns to the road more quickly, so the tyre maintains contact and the disturbance transmitted to the body is smaller. Both grip and comfort improve. The saving in total mass is real but small, and roll depends on the sprung mass and its height rather than on the unsprung components.

Answer: C

The wheel, tyre, hub, bearing and brake move entirely with the road surface and constitute the bulk of the unsprung mass. Suspension arms count as half sprung and half unsprung by convention. This is why inboard brakes were used on some designs and why large heavy wheels harm ride quality despite their appearance.

Answer: D

A larger wheel with a low profile tyre is heavier and has less sidewall compliance, so both the unsprung mass and the effective spring rate at the contact patch increase and the ride deteriorates. Steering response improves, which is the trade being made. Fuel economy generally worsens through the additional mass and rolling resistance.