Don’t mix tyres across the same axle – it’s dangerous, and can be illegal.

Don’t mix tyres across the same axle – it’s dangerous, and can be illegal.

28 May

By Tom Boote

As your tyre and automotive specialists, the Protyre team offer an unrivalled wealth of experience and expertise to UK mototrists. We know pretty much everything there is to know about tyres, including the variations and subtleties you’ll find between the wide array of different tyres on the market. It’s why our tyre team can offer you expert, impartial tyre advice.

Conversely – but unsurprisingly – for the vast majority of drivers, the view is that all tyres are more or less the same. Why? “Because they look the same”. It’s a common misconception, since, to the inexperienced eye, tyres can all appear to look the same as one another. But the truth is somewhat different, and vitally important to be aware of.

Why? Because, whether on purpose or by accident, if you mix tyres – particularly across the same axle – you could end up not just endangering your driver safety, but also find yourself on the wrong side of the law.
 

Differences between tyre types

So there are basically two differences between tyre types. The most obvious one – because it can be seen if you look carefully – is the variation in tyre tread patterns. Different premium tyre manufacturers, such as Continental, manufacture their own distinct tyre tread designs. If you were to spend some time looking at different tread designs, you’d soon notice the variations, and realise just how different these patterns are from each another... but more on this later.

The second, more significant difference, is the tyre construction itself. For the UK’s millions of car and van drivers, there are two main tyre build types that are fitted to their vehicles. These variations in build type are known as cross-ply and radial-ply. Each one has its own strengths and weaknesses, since they are designed and built to deal with the severe stresses of driving in different ways.

And it’s because of these different build and handling characteristics that you should never mix and fit them together, especially on the same axle. And don’t forget that just as the different tyre manufacturers create their own tread pattern designs, their tyres are also made using different compounds. These differ from one tyre maker to another, with each manufacturer having their own unique tyre compound ‘recipe’. It’s another reason why tyres perform differently from each other, and why it’s not a good idea to mix your tyres.


Don’t mix cross-ply and radial-ply tyres. Ever.

The tyres you’ll typically find fitted to your vehicle are made up of many plies – layers – including from rubber and cords of polyester, steel, or other textile materials. When these plies are fused together, they give tyres the strength and resilience they need to support your vehicle, keeping you safe on the road.

Cross-ply tyres are diagonally overlapped along the length of the tyre crown – the top surface of a tyre – down to the tyre sidewall (its side). This approach to arranging the plies creates a very solid, interlocked tyre structure. However, this means that the crown and the sidewall are dependent on each other for structural integrity. It also means the tyre will typically warm up significantly under severe driving stresses.

With radial-ply tyres, instead of forming an interlocking crown and sidewall, the plies are arranged radially – in other words, in the direction of travel. This means the plies are layered along the centre of the tyre – its length – and separate from the tyre sidewall. The crown and the sidewall are therefore independent of each other, and as a result this provides much more flexibility for the tyre. This manufacturing method also reduces heat build up within the tyre.

Croos-ply and radial-ply each offers drivers different benefits, depending on which vehicle they’re going to be fitted to, and the anticipated stresses from speed and weight loads they’re likely to experience. And this is the reason why you must not mix the two tyre types. If you do mix them, your vehicle won’t have a single, unified stress tolerance across all four tyres, and this means you’re at risk of incurring tyre damage and experiencing a blowout – which of course increases the chance of having a serious accident.

As such, mixing cross-ply and radial-ply tyres across the same axle is illegal in the UK.


Advantages of fitting radial-tyres include:

  • Improved steering and contact with the road
  • Better driving comfort due to flexible sidewalls
  • Reduced heat generation at high speeds
  • Higher resistance to tread-related damage
  • Lower rolling resistance, leading to reduced fuel consumption
 

Advantages of fitting cross-ply tyres include:

  • Significantly improved vehicle stability
  • Tougher, more resistant to sidewall damage
  • Cost less to manufacture, and subsequently to buy
  • Ideal for transporting heavy loads, such as for vans and light commercial vehicles


Can I mix different tyre tread patterns?

No. Mixing different tread patterns across the same axle is not allowed. The identical tyre model and tread pattern must be fitted for a single axle. You can, however, use different tyres on a separate axle – just as long as they too match each other.

That said, tyre experts – including Protyre, Continental, and TyreSafe – strongly recommend that you fit the same tyres on all wheel positions of your vehicle. Why? To ensure that you experience a consistent driving experience, without risking a diminished performance that often occurs when mixing tyres.
 

Just like for patterns, don’t mix your tread depths either

It’s also the case for tread depths. Don’t mix them, especially across the same axle. Why? Because if one tyre has greater tread depth than the other, it will clear any water on the road at a different rate to the tyre with less. This imbalance can lead to an increased risk of accident, since your vehicle has to cope with the stresses of different handling conditions that irregular water dispersion can cause.

It’s for this reason that tyre experts recommend that in the event you need to change a tyre – for instance, if you’ve had the misfortune to have suffered a puncture – that you do so for both tyres across the same axle.
 

Do not mix your tyre sizes either – it’s an absolute no-no

Leading tyre experts, like Continental, strongly recommend that you do not mix tyre sizes. Here’s their reasons why:
  1. You’re at risk of experiencing false speedometer readings if you have mismatched tyres, making you unaware of how fast you’re really travelling.
  2. Unequal tyres can adversely affect your car’s steering, acceleration, and general handling characteristics. You could experience less grip and reduced control, because the steering feels sloppy.
  3. Having unequal tyres can result in it taking longer for your car or van to get up to speed. This is especially dangerous if you require a sudden burst of speed so that you can avoid dangerous situation. Perhaps more importantly, it can also take you longer to come to a safe stop, when braking.
  4. If one of your tyres is wider than the others, this will typically cause you to experience serious instability, particularly in wet or icy conditions – just when you need the most control.
  5. In the long-term, having mismatched tyre sizes fitted will increase the risk of damaging your vehicle’s wheel bearings – with the possibility of destroying the clutch.
 

There’s one exception to the rule

It’s true. There are some cars – like some rear-wheel-drive Mercedes-Benz and BMWs – that come off the production line fitted with wider tyres on the rear wheels. However, this does not equate to a tyre size mismatch, since exactly the same tyres are fitted to any single axel, and the vehicle manufacturer has made a deliberate decision to enhance the traction on the rear driving wheels. The “Original Equipment” (OE) tyres that have been selected for this purpose are the result of a joint development initiative between both the vehicle and tyre manufacturers.
 

Talk to Protyre for expert tyre advice

If you’re in any doubt about mixing tyres – whether it be construction types, patterns, tread depths, or sizes – contact your local Protyre garage. Our experienced, expert team can provide you with impartial tyre advice, as well as the right fitting solution for your vehicle.

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