"Firmer springs" refer to the stiffness or resistance of the springs used in a vehicle's suspension system. It means that the springs are designed to support more weight and provide a harder and less bouncy ride. Full definition
A sport suspension with firmer springs and dampers will be part of a long options list. (autoweek.com)
The adaptive air suspension drops to Low Level and firms the spring rate. (porsche.com)
An optional sports suspension brings firmer springs and dampers, reduced ride height and a more aggressively configured limited - slip differential. (autoweek.com)