Automotive Driveline — Why Are Universal Joints Used at the Differential/Hub Ends? What is the principal reason for connecting drive shafts to the differential and wheel hubs through universal joints in vehicles with suspension travel and steering motion?

Introduction / Context:
Drivelines must transmit torque from the differential to the wheels while accommodating suspension movement, chassis roll, and steering angles. Universal joints (Cardan or constant-velocity types) provide the required flexibility while maintaining torque transmission.

Given Data / Assumptions:

• Vehicle has sprung suspension causing relative motion between axle/wheels and differential.
• Drive shafts must continue to deliver torque under changing angles.
• Focus is on geometric accommodation, not wheel speed splitting.

Concept / Approach:
A universal joint allows rotary power transmission when the input and output shafts are not collinear and when their relative angle varies dynamically. This prevents binding and fatigue that would occur with rigid couplings. Speed differentiation between left and right wheels is handled by the differential gears, not the U-joints.

Step-by-Step Solution:
Identify problem: suspension travel changes the shaft angle and distance.Functional requirement: maintain torque flow despite misalignment.Select the option describing geometric compensation due to road irregularities.

Verification / Alternative check:
Automotive texts show paired Cardan joints or CV joints at axle ends for angle and plunge accommodation.

Why Other Options Are Wrong:
Vibration absorption is a function of dampers and mounts; U-joints are not tuned vibration absorbers.Wheel speed difference in turns is provided by the differential, not universal joints.Gear reduction is achieved by gearsets, not joints.

Common Pitfalls:
Assuming a single Cardan provides constant velocity; it does not unless paired or replaced by a CV joint with proper phasing.

Final Answer:
compensate for variations in the relative positions of the differential and the wheels which result from bumpy road surfaces or other similar driving conditions.