Plus sizing is the practice of replacing an automotive wheel with one of a larger diameter fitted with a new tire of lower aspect ratio so that the new tire has close to the same diameter and circumference as the original tire to minimize any changes in speedometer accuracy, torque and traction control, while reducing sidewall flex and (generally) increasing cornering ability.
A "plus zero" upgrade means changing to a wider tire size while using the same diameter wheel.
The additional height and weight of plus-sized wheels may reduce vulnerability to rollovers, particularly by changing the center of gravity.
During rapid tire deflation at speed, reduced sidewall height may decrease rollovers.
With less unsprung weight, the shock absorbers and dampers are much better able to control the lower inertia and consequently, the vertical “bounce“ of a wheel over a bumpy road surface, resulting in better and more consistent tyre contact with the road surface.