Understanding tyre wear – causes and implications
We look at what your car's tyre wear says about the condition of your vehicle, and how to diagnose unusual wear patterns
It's no secret that the tyres on your vehicle need to be regularly maintained and kept in good condition. They're critical to the safety of you, your occupants, and other road users so it makes sense to understand what you need to check for, and the implications of having poorly maintained tyres. You can learn a lot from how a tyre wears to help you keep them in good condition.
Tyre treads are made up of tread blocks, raised platforms of rubber. The channels between the blocks are made up of grooves (which go around the tyre) and what are known as sipes (which generally go across the tyre) – these are what disperse standing water, without the sipes the car would be very dangerous in wet conditions and be very difficult to control. You may notice that the sipes, and tread blocks are all slightly different sizes, with some blocks slightly larger than others. If all the blocks were exactly the same the tyre would generate a loud, and monotonously irritating tone.
Types of tyre wear
By 'reading' the wear patterns you can decide whether the wear is normal and age/mileage related, or requires some adjustment to the vehicles suspension or tyre pressures.
If your tyre is wearing more in the centre then unless it's excessive, it's normal, particularly on the driven wheels of high powered, or aggressively driven cars. If the wear is excessive – if the centre is wearing much faster than the outer edges – then you could be running tyre pressures that are too high. Check you handbook for the correct pressure and readjust accordingly.
Heel and Toe Wear
Also called 'feathering' or 'sawtooth wear' this is where the tyre blocks wear down at an angle. If you run your hand over the tyre you can feel the 'sharp' edges of the blocks. Again, unless excessive this is not uncommon. If it is excessive it can cause the wheels to make unusually loud noises particularly when cornering (so loud they can be mistaken for damaged wheel bearings). This is most often seen on the vehicle's non-driven wheels. Excessive feathering can be caused by incorrect tyre pressures and alignment so it's worth getting them checked out. You can minimise the effect (if it's not caused by incorrectly set alignment) by swapping the wheels from front to rear, and side to side every few months.
If the tyre wears more heavily on the edge of the tyre, then this is likely to be due to the camber adjustment being incorrect, and is particularly common on lowered cars where the alignment hasn't been adjusted to compensate. The inner shoulder is more likely to be affected which can be dangerous, as it's often not spotted until the tyre is severely worn.
Running incorrect tyre pressures can have several negative effects, and not just incorrect tyre wear. An under-inflated tyre will get hotter than a correctly inflated tyre, which will impair performance, and speed up wear. It will also affect the handling and braking ability of your vehicle. Finally an under-inflated tyre will cause more drag, and as a result use more fuel and produce more pollutants. Pressures should be checked at monthly intervals, and always check the spare at the same time. A flat spare is no use to anyone!
Handy parts and tools:
When should you change your tyres?
The UK minimum tread depth is 1.6mm but it's advised that you should replace your tyres when they get to around 3mm. You can buy tyre depth indicators, or alternatively you could use a 20p coin as a guide. A 20p coin is 1.7mm thick, and the outer rim of the 20p is around 3mm, so if you place a 20p into the tyre groove upright it will indicate how near to 3mm the tyre is. You also need to check across the whole tyre width to check for uneven wear. Legally there needs to be 1.6mm across the centre 75% of the tread but we'd strongly advise changing a tyre that fell below this depth anywhere across the tread area.
Handy parts and tools:
So why should you change your tyres when there is still 'some' tread left? Well as we've discussed the grooves and sipes help channel water away in the event of you driving along a wet road. Without these grooves the tyre would effectively skim over the top of the water – an unpleasant and dangerous phenomenon known as 'aquaplaning'. The differences in performances between a brand new tyre, a part-worn tyre, and an illegal tyre are shocking. At 30mph on a wet road, a car fitted with brand new tyres will take around 26 metres to come to a stop. The same test carried out in a car with 3mm of tread left (so still well within the legal boundaries) will take around 35 metres to stop, which is approximately 35% further. Then compare that to a tyre on the legal limit of 1.6mm and the braking distance increases to 43 metres! It's pretty evident how important good condition tyres are!