A car comprising: a car body; and a rear spoiler, which is integral with the car body, is arranged in a rear position and projects from the outline of the car body to deflect the air flow upwards so that the air flow skims over an upper surface of said rear spoiler; wherein the rear spoiler comprises at least one through aerodynamic duct, which starts in an inlet opening arranged in correspondence with an initial end of the rear spoiler and ends in an outlet opening arranged in correspondence with a final end of the rear spoiler, so that a part of the air flow hitting the rear spoiler flows above the rear spoiler skimming over the upper surface of said rear spoiler and the remaining part of the air flow hitting the rear spoiler flows through the rear spoiler crossing the aerodynamic duct; the car is characterised in that: the aerodynamic duct has, on the inside, a narrowing, which is arranged in a central position along the aerodynamic duct and reduces the area of the cross section locally, i.e. only along a short section of the length when compared to the entire length of the aerodynamic duct; the area of the cross section of the aerodynamic duct is substantially constant along the entire extension of the aerodynamic duct, with the sole exception of the narrowing, so that the area of the cross section of the aerodynamic duct upstream of the narrowing is equal to the area of the cross section of the aerodynamic duct downstream of the narrowing; the narrowing consists of a deflector profile that projects towards the inside of the aerodynamic duct; and the deflector profile is movable so as to change its position on the inside of the aerodynamic duct. a car body; and a rear spoiler, which is integral with the car body, is arranged in a rear position and projects from the outline of the car body to deflect the air flow upwards so that the air flow skims over an upper surface of said rear spoiler; wherein the rear spoiler comprises at least one through aerodynamic duct, which starts in an inlet opening arranged in correspondence with an initial end of the rear spoiler and ends in an outlet opening arranged in correspondence with a final end of the rear spoiler, so that a part of the air flow hitting the rear spoiler flows above the rear spoiler skimming over the upper surface of said rear spoiler and the remaining part of the air flow hitting the rear spoiler flows through the rear spoiler crossing the aerodynamic duct; the car is characterised in that: the aerodynamic duct has, on the inside, a narrowing, which is arranged in a central position along the aerodynamic duct and reduces the area of the cross section locally, i.e. only along a short section of the length when compared to the entire length of the aerodynamic duct; the area of the cross section of the aerodynamic duct is substantially constant along the entire extension of the aerodynamic duct, with the sole exception of the narrowing, so that the area of the cross section of the aerodynamic duct upstream of the narrowing is equal to the area of the cross section of the aerodynamic duct downstream of the narrowing; the narrowing consists of a deflector profile that projects towards the inside of the aerodynamic duct; and the deflector profile is movable so as to change its position on the inside of the aerodynamic duct. the aerodynamic duct has, on the inside, a narrowing, which is arranged in a central position along the aerodynamic duct and reduces the area of the cross section locally, i.e. only along a short section of the length when compared to the entire length of the aerodynamic duct; the area of the cross section of the aerodynamic duct is substantially constant along the entire extension of the aerodynamic duct, with the sole exception of the narrowing, so that the area of the cross section of the aerodynamic duct upstream of the narrowing is equal to the area of the cross section of the aerodynamic duct downstream of the narrowing; the narrowing consists of a deflector profile that projects towards the inside of the aerodynamic duct; and the deflector profile is movable so as to change its position on the inside of the aerodynamic duct.