Ra­dial tyres

Evo India - - TECHNICALL­Y SPEAKING -

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.

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