The wheels feature run - flat tyres, which allow the vehicle to be driven over a certain distance even in the event of tyre pressure loss, thus enhancing safety. (press.bmwgroup.com)
This symbol indicates a flat or an air pressure loss in one or more tires. (myimprov.com)
A small difference may not trigger the system, but reduces the sensitivity to real pressure loss on the bigger wheel. (mechanics.stackexchange.com)