Everybody knows what a tyre is, but not many know why tyres come in all different sizes. Explaining all of the variations makes the subject very technical and complicated. Here we endeavour to simplify some of the concepts and technical jargon.

Soon after man invented the wheel he realised that it wore out as he used it. A piece of material was then wrapped around the outside of the wheel either to rebuild it or prevent it from wearing out. This material wrapped around the outside of the wheel became known as a “tyre”.

In our modern world there are two types of tyres: solid and pneumatic:

• Solid tyres were the original type of tyre used. As the name suggests they are made up of some type of solid material that is wrapped around the wheel. There are many different types of solid tyres, which will be explained later.
• Pneumatic tyres have air pressure inside the tyre. The pneumatic tyre must be fitted to the outside of the wheel and inflated with air pressure. There are three types of pneumatic tyres: bias ply, bias belted and radial ply.

There is one simple difference between the solid tyre and the pneumatic tyre: A solid tyre pushes into the road surface and the pneumatic tyre sits on top of the road surface.

Say you are pushing a wheel barrow load of bricks over the lawn. If the wheel barrow had a solid wheel it would dig a rut into the lawn and get stuck, and it would be difficult to push. A wheelbarrow with a pneumatic tyre would roll over the lawn, leaving a small wheel mark, and it would be easy to push. In other words, the solid tyre digs into the soft lawn surface and the pneumatic tyre “floats” over the soft lawn surface.

What happens if you push the wheelbarrows over a hard concrete footpath? You would find that it is easier to push the wheelbarrow with the solid wheel than the one with the soft pneumatic tyre. This is because the solid wheel sits on top of the hard concrete surface and rolls easily, while the pneumatic tyre squashes out and deforms over the surface making it harder to push. The more air pressure you put into the pneumatic tyre the easier it is to push over the concrete foot-path.

The pneumatic tyre is very sensitive to the air pressure inside the tyre where the solid tyre is very sensitive to surface it is running on – this is the primary difference between solid and pneumatic tyres.

Different Types of Solid Tyres

The first difference in solid tyres is the type of material that the solid tyre is made from. The material could be steel, rubber, wood, leather or some type of man-made plastic material.

The second difference is the type of solid tyre - how it is made. Some are completely solid, others are hollow inside, some are filled with foam and some are pressurised inside. There are many other variations with springs and layered materials inside.

Different Types of Pneumatic Tyres

All pneumatic tyres are made of rubber reinforced with tyre cord. The three different types of pneumatic tyres - bias, bias-belted and radial - explain the different ways in which the tyre cord is place inside the tyre. Solid tyres do not have tyre cord inside to hold the air pressure.

In simple terms, a pneumatic tyre is made up of rubber just like a party balloon. The rubber party balloon is blown up with air pressure. The more air you put inside it the balloon gets bigger and bigger.

A rubber tyre is the same except tyre cord is put inside the rubber balloon to hold its shape against the increasing air pressure. The way in which this tyre cord is placed inside the tyre determines its type.

Solid tyres differ from pneumatic tyres as pneumatic tyres need air pressure inside them to work. The tyre cord inside them holds the tyre’s shape and determines what type of pneumatic tyre it is.