Most tyre manufacturers recommend tyres to be used for a maximum period of six years. Well, using a tyre for that long in varying conditions is a risk by itself. You can do a regular check on the tyres yourself. Inspect the sides of the tyre for word DOT which is followed by a series of numbers for example DOT 51 16 which states the tyre was manufactured in the 51st week of 2016. Check for surface cracks and eroding rubber that tends to develop on the side walls, which gives you a clear warning as to how bad the tyre is.