First production car application: Citroën 11 When: 1946
Pneumatic tyres remained practically unchanged from the first air-filled items in use from the late 19th century until 1946, when Michelin filed a patent for its revolutionary new radial-ply tyre.
Before radial tyres, most cars and trucks ran on crossply tyres. The cords that make up the carcass of a crossply tyre span, at an angle, from one bead to the other, with each layer of cords at opposing angles – hence the name. The tread and sidewall are supported by the same cords.
For radial tyres, the angled cords are replaced with ones that still stretch from bead to bead but perpendicular to the direction of rotation. A belt that follows the circumference of the tyre then supports the tread area. This belt can be made from steel, polyester or Kevlar.
One of the reasons radial tyres became popular is because they have a lower rolling resistance than crossply tyres and so are more fuelefficient, despite being heavier. A radial tyre’s tread distorts less during cornering, too, so it can provide greater levels of grip. However, a crossply tyre has a larger slip angle, which makes a car’s steering feel less precise but the chassis more progressive when losing grip. As radial tyres became more common, car makers altered suspension and steering setups to work better with the attributes of the new tyres.