"Chassis upgrades" refer to improvements or modifications made to the frame or structure of a vehicle, typically to enhance its performance, stability, or handling capabilities. Full definition
The engine sounds fantastic and the handling becomes so much sharper thanks to stiffer springs and a number of other chassis upgrades. (autoexpress.co.uk)
It also gets chassis upgrades in the form of front and rear tunnel stays. (motoring.com.au)
Other chassis upgrades include Brembo brakes with red calipers to reduce braking distances, and bigger 18 - inch alloy wheels, dubbed «Titanium Quadrifoglio Verde». (motoring.com.au)