WHEN TO CHANGE YOUR TYRES

The first thing to look at is tread depth. A Euro is an excellent tool for this. Turn the Euro upside down, and stick the Euro into the tread groove. If you can see the top of number 1, the tyre doesn't have enough tread to be safe (or legal, for that matter). Of course, auto supply stores have tread depth gauges that are inexpensive and easy to use.

Tyres also have built-in wear indicators: each tread groove will have a four or five spots around the tyre that are 2/32 of an inch (the minimum legal tread depth) higher than the rest of the groove. These high spots will create a visible gap in the groove once the tread has worn down to 2/32".

Don't just look at one tread groove, either. Check several, to see if one part of the tyre is wearing faster than another. Also, look for "cupping," which is a series of flat spots on the edge of the tread; look at the sidewalls for bulges, which indicate a problem with the tyre's internal structure. If you can see wire mesh or threads anywhere, that tyre is worse than worn out-it may not be safe to drive on. A tyre showing any of these conditions needs to be replaced.

A change in your driving pattern may call for new tyres before they wear out, however. A move from a town to the mountains, may mean you'll be in the market for snow tyres; if you'll be using what was previously an off-road vehicle on pavement, you may find you need tyres better-suited to asphalt.

Finally, emotion can even play a part in tyre buying: you might just like the way a certain tyre makes your vehicle look, or you may be very interested in new tyre technologies like run-flats.