how a tyre works
1 Beaded edge tyres
Nearly all automotive tyres contain a steel bead within the contact point with the wheel rim. But early pneumatic car tyres featured an additional moulded area which sat inside the shape of crosssectional shape of the rim. This was an attempt to overcome the tendency for tyres to leave rims, under the influence of compressed air pressure and centrifugal force.
Still with steel beads at the rim edge, but now fitting onto wheels with wells, lessening the tendency to throw off the tyre, construction featured layers or ‘plies’ stretching from bead to bead. This gave the tyre walls a rigid construction offering good directional control. The lack of sidewall ‘give’ on cornering led to easy loss of grip on enthusiastic cornering.
The construction of radial tyres revolutionised grip on cornering and at speed, keeping a greater tread area in contact on the road when under the influence of sideways forces, although the softer walls also led to heavier steering characteristics, especially when retro-fitted to older cars. Here, flexible ‘carcass’ plies extend from bead to bead, with steel reinforced ‘radial’ plies in place around the tread and top shoulder areas of the tyre.