Your tyres are very good at giving you an indication of the condition of your front and rear suspension and steering systems. They can also tell you if you’ve been bad and haven’t kept an eye on their pressures as well. Know-all little buggers they are!
Below is a list of the most common tyre wear patterns and their likely causes. This list is by no means exhaustive but it should give you a good idea of what is going on if you have some odd tyre wear patterns going on.
Tread Depth Indicator
The first and probably most important is the tread depth indicator bar. Nothing too scientific here, when the surrounding tread reached the same ‘height’ of the indicator bar it’s time to replace the tyre because the tread is at it’s legal minimum depth.
Over-Inflattion and Under-Inflattion
Tyres that show wear on both edges indicate either under inflation (low air pressure, anything below 30psi could cause this) or overloading of the vehicle. Front wheel drives in particular suffer from this type of wear, most likely because of the weight of the engine and gearbox being directly over the front tyres.
Taking cold tyre pressures to 34psi on a front wheel drive can help to reduce this wear.
Abnormal wear down the centre of the tread area indicates over inflation or too high air pressure in the tyre. This causes the tread to take on a concave shape and reduces the amount of tyre in contact with the road and rapidly wears out the part of the tread that is in contact with the road surface.
Wear On One Side
Tyres that are worn abnormally on either side of their tread are usually the product of bad wheel alignment however there is a number of other causes to consider. Sagged coil springs on Macpherson Strut suspension can alter the camber angle and cause this type of wear. Worn control arm bushes, excessive play in wheel bearings, overloading on Independent Rear Suspension equipped vehicles (namely VR/VS Commodores – there is a bush kit for the rear arms available to correct the camber angle on these cars) and bent axle housing or stub axle.
Irregular Tread Wear
If you find you have a tyre (or tyres) with irregular wear similar to the picture then chances are you have worn shock absorbers. As the car is bouncing over bumps in the road the downward pressure on the tyre is changing causing these wear patterns. Wheel balance, play in wheel bearings and worn suspension joints can play a part in this also. Four-wheel-drives with worn shocks seem to be prone to this type of wear and early detection is important if you don’t want to shell out for a new set of tyres and shocks in one hit!
The last one that I have pictures for is feathering of the edges of the tread which is generally caused by excessive toe-in or toe-out and provided the suspension and steering are in good condition, it can be corrected with a wheel alignment.
One other issue we see a lot of these days is ‘tread seperation’ where a portion of the tread area becomes raised like a ‘bubble’ in the tyre. It will be felt in the car as a vibration and at low speed you can feel when the tyre is lifting as the raised area contacts the road. I believe this can be due to many factors and the age of the tyre and the load it has to carry has a lot to do with it.
Tyres fitted to caravans and trailers for instance seem to be prone to tread separation. One reason I have heard for this is because they are left in the one spot for a lengthy period of time, this causes the steel belts to flatten out to a certain degree and when they are used they are usually carrying a fair load which places even more stress on the tyre. If someone has a better explanation for this, please let me know!
The most important things to remember with tyres is to check your pressures regularly, have the tyres rotated at no more than 10,000km intervals (I do mine at 5000km’s and I get great mileage out of them) and keep a close eye on how they are wearing so you can identify any problems before you have to replace your tyres prematurely.