Pneu­matic tyre ev­ery­thing You need to know

Fuzz shares the grip­ping tale be­hind your car’s boots

Classic Car Weekly (UK) - - Living With Classic - fuzz town­shend ccw’s mas­ter me­chanic

‘Come the 1950s, even low-slung cars were still tee­ter­ing on the tyre equiv­a­lent of stiletto heels’

N owa­days, the word ‘tyre’ in­stantly brings to mind cir­cu­lar rub­ber semi­tubes, filled with com­pressed air. But not ev­ery tyre is re­lated to the prod­uct of fi­cus

elas­tica – aka the rub­ber tree. Any ex­ter­nal, wear­ing com­po­nent of a wheel may be termed a tyre, from rope, through metal to rub­ber and its syn­thetic de­riv­a­tives, hence the use of the term for the en­cir­cling bands of steel on an­cient horse­drawn carts and trams. Au­to­mo­tive tyres of the past 100 years should be thought of in cross-sec­tion, when think­ing of con­struc­tion and char­ac­ter­is­tics; in essence an in­verted horse­shoe shape.

For most clas­sic car own­ers in the UK and Europe, tyres fall into two main cat­e­gories: crossply and ra­dial. Their names re­late en­tirely to their con­struc­tion and the two types can of­fer very dif­fer­ent char­ac­ter­is­tics.

The grand­daddy of au­to­mo­tive pneu­matic tyres was the sep­a­rate in­ner tube-filled, bead-edged crossply. The bead en­abled the tyre to fit snugly into the rim of the wheel while keep­ing a se­cure grip. This pre­vented the ac­tion of the in­ner tube’s in­fla­tion from ex­pand­ing the tyre away from the wheel.

Steel cords were moulded into the seat of the tyre walls, pro­vid­ing a slightly bul­bous sec­tion to grip onto the in­ner edge of cor­re­spond­ingly-shaped wheel rims. With the in­ner tube in­flated, the beads pushed un­der the rim edges, se­cur­ing the tyre, while the in­fla­tion stiff­ened the walls and pushed the tread away from the wheel, sep­a­rat­ing road sur­face from sus­pen­sion through the medium of com­pressed air. Ge­nius, Mr Dun­lop.

The trou­ble was that these nar­row tyres needed plenty of struc­tural stiff­ness and a lot of pres­sure to keep them in place; the con­tact area be­tween the tread and the road was lit­tle bet­ter than the sur­face area of a postage stamp.

By the end of the 1930s, the stiff side­walls and steel beads con­tin­ued to an ex­tent, but the lat­ter was much di­min­ished, ow­ing to the greater abil­ity of the tyre to re­main of the same in­ner circumference and to the in­clu­sion of a ‘well’ in the wheel rim. This lat­ter meant that the in­ner tube was now par­tially sub­merged within the wheel, al­low­ing lower tyre pres­sures and greater con­tact area be­tween tread and road.

Come the 1950s, even low-slung cars were still tee­ter­ing on the tyre equiv­a­lent of stiletto heels. They needed the train­ing shoe, er, ra­dial tyre.

Ra­di­als’ sup­ple side­walls keep more of the tread sur­face in con­tact with the road, es­pe­cially at speed and on cor­ner­ing, lead­ing to much en­hanced road hold­ing.

How­ever, fit­ting such tyres to cars de­signed with cross­plies in mind, led to heav­ier steer­ing and leaf sprung rear ends now with so much give that they mim­icked hot­pants-clad dancers on pop­u­lar mu­sic tele­vi­sion shows.

En­hance­ments in sus­pen­sion de­sign coun­tered these ob­sta­cles, lead­ing to the sure­foot­ed­ness of cars that we take for granted to­day.

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