Chassis Layout and Frames Questions and Answers

Answer: C

The classical layout places the engine ahead of the passenger compartment with a propeller shaft carrying the drive back to a live or independent rear axle. It gives good weight distribution and separates the steering from the driving wheels. Its costs are the transmission tunnel intruding into the cabin and the extra weight and complexity of the propeller shaft and rear differential. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: D

Mounting the engine transversely with the gearbox and final drive in one unit removes the propeller shaft and the transmission tunnel, freeing a great deal of interior space for a given overall length. It is also cheaper to manufacture. Weight transfer under acceleration unloads the front wheels and reduces traction, which is the layout's principal dynamic disadvantage. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: A

The front tyres must generate both cornering and driving forces, so they reach their friction limit before the rear tyres and the car runs wide. Manufacturers generally tune for understeer in any case, because it is the more forgiving behaviour for an inexperienced driver. Lifting off the throttle in a front wheel drive car transfers weight forward and can produce a sudden tuck in. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

A mid engine placement concentrates the mass near the centre of the wheelbase, minimising the polar moment of inertia and giving very responsive handling. It is standard for racing cars and high performance road cars. The penalties are the loss of interior and luggage space and the difficulty of access for servicing.

Answer: C

Concentrating the masses near the centre reduces the resistance to yaw acceleration, so the car changes direction more readily and responds more quickly to steering input. Unsprung mass concerns the wheels and suspension rather than the engine. Centre of gravity height depends on how low the engine sits rather than on its fore and aft position. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: D

The Beetle placed an air cooled flat four engine behind the rear axle driving the rear wheels, which gave excellent traction on poor surfaces and allowed a simple flat floor. The penalty was a strong rearward weight bias producing snap oversteer at the limit. Porsche has retained the layout in the 911 while progressively engineering out the handling problem. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

The large polar moment of inertia and the rearward weight bias mean that once the rear tyres break away the car rotates rapidly and is difficult to catch. Traction under acceleration is excellent, which is the layout's principal virtue. Modern electronic stability control and careful suspension geometry have largely tamed the behaviour. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

Four wheel drive divides the torque between the front and rear axles through a transfer case and a centre differential, greatly improving traction on loose or slippery surfaces. Part time systems lock the two axles together and must not be used on dry tarmac, while full time systems use a differential or a viscous coupling to permit the speed difference that cornering requires. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: C

The front and rear axles travel different distances through a corner, so a differential or a compliant coupling between them is essential if wind up is to be avoided. A part time system without one must be disengaged on high grip surfaces. A viscous coupling transmits torque progressively rather than locking rigidly, which is why it can serve the purpose. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: D

With no differential between the axles and no slip available at the tyres, the difference in path length through a corner strains the transmission until something slips or breaks. On loose surfaces the tyres slip and relieve the strain. Wear occurs at all four wheels and the primary failure is mechanical rather than thermal.