Cross-Ply & Radial Tyres

I originally wrote this article in 2008 for my podcast after I had found an old TV advertisement on YouTube showing the dangers of mixing cross-ply and radial tyres on the same axle. The result could be circular driving with ends swapping direction!

The tyre as we know it today came from the minds of two Scotsmen: John Boyd Dunlop and Robert Thomson who both developed and patented designs for pneumatic tyres. Up until then wheels had been covered in fabric or solid vulcanised rubber – which was invented a decade earlier by Charles Goodyear. Adding air in the tyre made the ride more comfortable. Incidentally Charles Goodyear was not connected to the tyre company. It was named in honour of him though.

Cross-Ply Tyres
As the automobile industry was forming from the bicycle industry, several concepts jumped over including pneumatic tyres. By 1915, the Palmer Tyre company in Detroit had developed a tyre by adding in belts of rubberised fabric to strengthen the tyre before the tread was moulded. Each belt was laid in an alternate diagonal pattern of about 30 – 60 degrees (I have read several articles defining different degrees of the pattern from 30 to 60). The diagonal layering may have evolved over the years to provide a different feel for specific uses hence the wide spread of numbers. These diagonal patterns lead to the name cross-ply or bias tyre.

In the early years, tyres had cord belts dipped in rubber, then Goodyear introduced rayon belts before improving them further to nylon cords. The tyres also had tubes as well. By 1954, Goodyear had advanced to tubeless as they are today on most vehicles. Then in 1959, steel belted cross-ply tyres were introduced.

The structure of the cross-ply tyre meant that there was high friction with the tyre not making full contact with the road (i.e. some slippage) and to make it worse, the belts and sidewalls shared the same underpinnings so there was a fair bit of deformation of the tyre under load.

Radial Tyres
Interestingly, radial tyres were first patented in the same year that Palmer was introducing cross-ply tyres. Arthur W. Savage, a colourful inventor who travelled the world and is mostly famous for designing firearms patented a new tyre. He had set up the Savage Tire Company in San Diego and his patent was only for the US and expired in 1949. I have not found examples of their products – the market would have been dominated by Goodyear and others selling cross-plys.

In Europe, Michelin had developed their version of the radial tyre by 1946 to improve the performance of their products. They got to the market in 1948 thanks to their ownership of Citroen but it wasn’t until the late 1960s that the radial tyre reached the US market. Up until then, cross-ply tyres were the normal type of car tyre.

What Savage Tire and Michelin did was to make the belts directional on the tyre i.e. radial-ply, which meant that the tyre squatted on the road providing reduced friction and much higher grip. The reduced friction improved fuel economy and the increased grip increased steering and cornering ability, making them safer in good weather conditions. In addition, the tyre had improved tyre wear which meant that although they were more expensive to manufacture, they lasted longer.

Radials are now the normal tyre and in recent years much more research has been done to ensure a better tread pattern and a better carcass structure with different compounds of rubber for different applications. For example, the Bridgestone tyres I had as standard fit on my Honda had a softer compound than a tyre designed for a family wagon. Extending that further, Pirelli make tyres for my bike with different compounds for the centre and sides – the sides are softer to provide better grip when cornering.

Tyres are an important component of a vehicle and care should be taken to look after them. If they are maintained in good condition they will help to reduce fuel usage and with good grip will help under braking and acceleration. As they are the only pieces of the vehicle touching the ground they are also an important safety device, worn tyres can increase the chances of an accident or loss of control.