Pneumatic tyre everything You need to know
Fuzz shares the gripping tale behind your car’s boots
‘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.