When It Comes To Rubbers, Here’s Why Size Matters (Tyres)

When It Comes To Rubbers, Here’s Why Size Matters (Tyres)

They say size doesn’t matter. Yes, we are talking about lyres.

This Murano Ti is a Z50 model, all-wheel drive with 162,500 kilometres on the clock .

After a few tyre replacements over time, the vehicle ended up with different size tyres on the front and rear.

While driving down the road, the rear diff exploded, completely destroying itself.

The ability of all-wheel drive vehicles to divide the engine ‘s horsepower between its four tyres is useful on loose or slippery surfaces, but in order to transfer this extra power, the vehicle ‘s driveline mechanically connects the tyres so they work in unison.

All-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tyre.

tire-size-differential-damage

However, if the differentials or viscous couplings are forced to operate 100 per cent of the time because of mismatched tyres, they will experience excessive heat and unwarranted wear until they fail.

This means that all-wheel drive vehicles must use tyres that are very closely matched. Different diameter tyres roll a different number of times over every kilometre.

Tyre diameter variations are not just limited to the accidental purchase of different size tyres. The same catastrophic result can happen with tyres with different tread designs, tyres made by different manufacturers, different inflation pressures or even tyres worn to different tread depths.

Compare two 215/65  R16 tyres- one with the original tread depth of about 8 mm and the other down to the wear indicators. The circumference of the new tyre is 2,150 mm. The worn tyre measures 2,100 mm.

The difference of 50 mm might not seem a lot, but at 100 kilometres an hour on the highway, it soon adds up. This difference will cause a continuous strain on the tyres and the vehicle’s driveline. Obviously, the greater the difference in the tyre circumferences, the greater the strain on the vehicle.

Cutting corners with tyres is not an option. The vehicle’s recommended tyre pressures must be maintained and all tyres must be matched.

Matched tyres means all four tyres are the same brand, design and tread depth.

Mix them up and you are asking too much of the driveline. Mismatched tyres or wrong inflation pressures for all-wheel drive and four-wheel drive vehicles can also result in immediate drivability problems.

Some traction control equipped vehicles in auto mode may shudder on acceleration or a noise will be heard from the front driveline and transfer case when the vehicle is being driven. Some of these vehicles may exhibit axle wind­ up or binding while driving.

In the case documented in this story, the owners had ignored all the signs. Their vehicle was literally screaming for attention. There had been an audible noise from the driveline for some time and on the day the diff gave up, the noise was deafening .

The owner was wishing he had acted on the noise – his bank balance is now doing the screaming.

When It Comes To Rubbers, Here’s Why Size Matters (Tyres)
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