Trying to wring out the last mile from your tyres? Think Again

In the previous post, I wrote about people trying to run their tyres bare. Here is why this is a bad idea.

We tend to use our cars at higher speeds today than our parents did back in the day. To make matters worse, traffic congestion is on the up and we probably brake harder than our parents did more often than they did. Clearly you need tyres that can stop quickly under hard braking, and a bald or nearly bald tyre is going to slide smoothly over smooth tarmac rather than stop.

So what is a good indicator of when to change you tyres? Before most tyre manufacturers built a Tread Wear Indicator or TWI into the tyre tread pattern, the standard test to use was the penny test or Lincoln Head test for tread wear. The TWI enables you to check remaining tread depth visually, because, let's face it, most of us don't carry a penny around with us - let alone, one with a Lincoln Head.

The Tread Wear Indicator is essentially a bump in the rubber at the bottom of each groove in the tread pattern. Click here for image. This bump is between 1/16th of an inch and 1/8th of an inch. When your tread wears down to the point that the TWI bumps are flush with your tread tops, it is time to change the tyres. Most tyres will also mark along the wall of the tyres to tell you where the TWI bumps are located.

Here are some pictures of TWI on new tyres and on worn tyres.