Tyre testing

There’s no getting away from it – tyres are expensive. The growth in sizes in recent years has seen replacement costs rise significantly, so now, owners of even basic family cars can easily pay £100 a corner. A new set of tyres is often a distress purchase, with drivers needing to make a decision quickly as their car has a puncture, for example. And as Auto Express’s inbox and postbag can testify, wear is a key factor in their choice.

The trouble is, when responding to readers’ queries, it’s impossible for us to provide an accurate idea of how long a particular make and model of tyre should last. This is because a wide range of factors affects how quickly any brand of rubber reaches those 1.6mm minimum tread bars. Our guide spells these out – and it should help you get a few more miles out of your tyres.

Main factors in tyre wear

1. Where you drive has the biggest bearing on how fast your tyres wear. If you spend a lot of time on winding, hilly roads, they are used harder than if you pound up and down motorways, as it is the forces applied to the tyre that creates wear.

Motorists who stick mainly to twisty mountain roads will need to fit new rubber up to two-and-a-half-times sooner than the average driver who use all types of highway. If you spend a lot of time on motorways, you should get twice the mileage out of your tyres than these ‘normal’ motorists – this is because even though speeds are high, cornering and braking forces are low.

Drive all the time in town, and you can expect a 10 per cent improvement over the ‘mixed’ motorists, mainly because cornering forces are low while those for braking are high. Extreme temperatures accelerate wear, too.

2. For most drivers, the kind of road used is the major cause of wear. But hard driving – especially in powerful front-wheel-drive cars – can be an even bigger factor. Heavy accelerating and braking, along with fast cornering, will eat through tyres, particularly when it’s the front wheels that brake, turn and pull the car. You can maximise the life of your rubber by avoiding aggressive throttle, steering and brake pedal inputs.

3. The effects of where and how you drive can be exaggerated by the vehicle you run. The bigger and heavier it is, the more extreme the forces put through the tyres – and so the faster the tread is lost. Suspension geometry plays a part here, either through aggressive standard settings found on some performance cars, or through the alignment being knocked out by potholes or kerbing.

Even small deviations from the correct setting can accelerate wear significantly. These problems usually lead to uneven depth, both across the tyre and between sides of the car.

4. Failing to check your tyres’ pressures will mean a tripto the garage sooner than necessary. Whether the readings are too high or too low, wear is increased.

The latter is more common, as owners often neglect to check their rubber. British drivers are the worst in Europe for this. An amazing 85 per cent of cars on the roads in this country have at least one underinflated tyre, while around 60 per cent are at least 10psi out.

Checking tyre pressures isn’t only a wear issue, however; it can also have a major bearing on safety.

In France, one in every 12 fatal accidents is linked to underinflation.

5. The final major influence is what you carry in the car. If you drive a vehicle loaded with luggage or packed with passengers, you will get through your rubber more quickly than if you travel light and alone. So don’t leave the boot packed with kit you don’t need, and remove roof boxes and bars if they’re not in use.

The best way to calculate how long tyres take to reach the 1.6mm minimum tread is to drive thousands of miles. So that is exactly what independent testing body TüV Sud did when commissioned by Michelin to compare the French brand’s rubber against rivals.

To eliminate all the variables, identical Skoda Octavias were driven in convoy on a specially selected 2,000km circuit in the Czech Republic. Drivers and tyres were switched from car to car, and vehicles moved within the convoy to ensure that, at the end of the assessment, all the tyres had done the same mileage on each Octavia, with the same driver and position within the convoy.Tyres were measured daily at 24 points, and the circuits repeated until a reliable ‘wear rate’ was achieved.

Using this, engineers calculated when the tread depths would reach 1.6mm. Two sizes of rubber were tested: a 16-inch tyre was run over 14,000km and a 17-inch one on a more abrasive 8,000km circuit.

We list the results below, giving the top rubber 100 per cent and the rest a relative score. TüV and Michelin focus on relative performance between the brands rather than referring to tyre life in distance. But the figures suggest the best 16-inch rubber under these test conditions covered around 20,000 miles and the worst a little less than 13,000 miles. For the bigger size on the harsher circuit, the figures were around 16,000 and 8,000 miles respectively.

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