A family car today weighs considerably more than its equivalent from a few decades ago, despite lighter materials being available. The increase is the accumulation of several separate demands, each reasonable on its own.
What crash protection costs in mass
Modern bodies contain deliberately engineered crumple zones, high-strength steel in the passenger cell, and reinforcement in the doors and roof.
Side impact and roof crush requirements are particularly demanding because there is little space to absorb energy, so the answer is stronger and heavier structure.
Airbags, their sensors and the structures that support them add further mass distributed around the cabin.
Why equipment accumulates
Air conditioning, electric windows, powered seats, sound insulation, larger screens and multiple control units are now standard on cars where they were once optional or absent.
Each item is modest alone, and collectively they represent a substantial share of the increase.
Wiring is an underappreciated part of it, since the harness connecting these systems is itself one of the heaviest single components in a modern car.
How cars simply got bigger
Successive generations of the same model name have grown in every dimension, partly to meet crash requirements and partly because buyers expect more interior space.
A larger body means more material, larger glass, bigger wheels and tyres, and a larger cooling system.
The shift toward higher vehicles compounds it further, since a raised body needs more structure and more glass area for the same interior room.
Why one addition forces another
Mass is self-reinforcing. A heavier car needs larger brakes to stop it, stronger suspension to control it and a bigger engine or motor to move it acceptably.
Each of those components is itself heavier, which raises the requirement again, and the loop only settles at a higher total.
Working the loop in reverse is the reason weight reduction programmes achieve more than the parts list suggests, since removing mass allows other components to shrink.
What electrification did to the trend
A battery large enough for useful range is far heavier than a fuel tank, and the structure protecting it from intrusion adds more.
Manufacturers offset some of this with aluminium body panels, composite components and casting techniques that replace many stamped parts with one.
The offsetting has slowed the increase rather than reversed it, and heavier vehicles bring consequences for tyre wear, road surfaces and the energy needed to move them that are now being examined directly.