Can my wheels be too big and is it illegal?

TYRES are one of the most important components of any car so be sure they meet the legal requirements.

Many drivers could be on their travels using tyres that are considered too big for the vehicle, and what's more they may not even know they're breaking the law.

One of the most critical aspects of road safety is the size and conditions of your car tyres.

Some drivers may have experienced their tyre light flashing on the dashboard to indicate a flat, or that the wheel is in need of some other roadside attention.

Having a non-approved tyre might not trigger your warning light to flash, but you could unknowingly be compromising the safety of yourself and other road users.

Approved or non-approved

The approved tyre dimensions are specific to the make and model of your vehicle.

While some people like to keep their cars the way they came out of the factory, others like to enhance it by changing the size of their tyres.

Drivers need to be aware that the dimensions provided by the car manufacturer are all approved for each vehicle and are calculated to balance the cars size and weight.

Your approved tyre dimensions for your particular vehicle are indicated on the sticker in the driver's door or in the owner's manual, and sometimes also in the fuel filler flap.

There is nothing wrong with updating your tyres, but choosing the approved tyre size for your vehicle will ensure it's safe to use.

The law states

Tyres can be classed illegal if they are deemed unsafe for the size of your vehicle.

The following factors will be considered when deciding if your tyres are within the legal limit:

• Wheel offset - If the wheel offset is too big, the wheel can protrude out of the arch, which is illegal.  To avoid this a qualified mechanic can help design custom alloy wheels with an offset that doesn't break safety laws
• Rubbing on arches - Tyres that rub on the wheel arches are illegal
• Suspension and speedometer - The stock diameter and width of the wheels and tyres directly affects the suspension and speedometer, therefore this will need to be checked in relation to any non-approved tyres fitted
• Speed recalibration - If you go for bigger tyres, you'll need to replace the rims on your car. This mean drivers will also need to recalibrate their speedometer to compensate for the change in tyre size
• MOT - Having tyres of different sizes on the same axle will cause your car to fail its MOT. This is because it affects the stability and handling of the car

Another critical aspects of tyre safety is the tread depth.

In the UK, the legal minimum tread depth for car tyres is 1.6 millimeters across the central three-quarters of the tread width and around the entire circumference of the tyre.

Driving with tyres below this limit is not only dangerous but also illegal.

If your tyres don’t meet legal standards, you could face a fine of up to £2,500 and three penalty points on your license per tyre.

Can I fit a different size than the approved ones?

Whilst you can fit different sized tyres to your vehicle, it is recommended to follow the tyre sizes approved by the manufacturer to ensure road safety.

In some countries, an exemption is possible provided that the tyre diameter remains within a limit of no more than -2% and +1.5%.

By choosing non-approved sizes, you could, for example, fit tyres that are too wide and protrude dangerously beyond the width of the vehicle - making it illegal.

Or you could be fitting tyres with an insufficient load index, which has serious implications.

The load index is a number that indicates the maximum amount of weight a tyre can bear at its speed rating when inflated to its maximum pressure.

Fitting tyres with an insufficient load index can be dangerous and illegal.

It could also void the warranty on your vehicle and your insurance may refuse to pay a claim if your car has tyres that do not comply with the manufacturer's recommendations. 

You can find the recommended load index for your vehicle in your vehicle handbook. 

In addition, fitting non-approved tyres could compromise the accuracy, as well as the number of kilometres on your speedometer.

This is because the speedometer takes into account the diameter of your wheels when tracking your speed and distance.

Alloy Modifications

Some motorists enjoy enhancing their vehicles aesthetic by making some modifications to the wheels.

Much like a cars tyres, alloys are perfectly legal to change, so long as they match the dimensions of your existing alloys.

Motorists will also have to consider the wheel offset, which is measured by how far out of the rim the alloy is placed.

If the offset is too big and protrudes out of the wheel arch, this can break safety laws.

Informing your insurance company of any changes made to your car is advised to keep your insurance valid.