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Tue, 21/03/2017
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Be Wiser’s Guide to Car Modification

What Is A Car Modification?

A car modification is any change made to a vehicle that isn’t part of the original manufacturer’s specification. Many drivers like to make changes to their cars to personalise them, to improve the way they look, and to make them perform better. From spoilers to powerful engines, there are many ways you can modify your car.

But not everyone understands the full extent which car modifications can affect your car insurance premiums, and the dangers modifying your car can bring.

How Could Car Modifications Affect Your Insurance?

Car modifications can affect your insurance premiums, so it’s important to declare them to your insurance company – even if they seem insignificant, or if you didn’t make the modifications yourself. Insurance is based on risk, and modifications can affect this risk if they increase your chance of having an accident, or increase the chance of the car being stolen or broken into. Some modifications are considered lower risk than others, such as tinted windows and alloy wheels, whereas modifications which could have a bigger impact on performance are considered higher risk – such as fitting a more powerful engine. If you don’t declare the modifications, your insurance may be invalidated and you won’t be able to make a claim if the worst should happen.

It’s better to declare any modifications and pay a higher monthly or annual premium, than it is to leave them undeclared and risk invalidating your policy and being unable to make a claim when you need to. If you do make a change to your car, let your insurer know as soon as you do so (or even beforehand), and find out whether it will have an effect on your policy.

Car Modifications With An Increased Accident Risk

Engine and Mechanics

If you have added a turbo or supercharger to your engine, or made any other modifications to the engine or mechanics, including the exhaust, transmission or air filter, you need to let your insurance provider know. These modifications could increase the risk of an accident and affect the cost of your premium.

Changes to your engine control unit (ECU) also need to be declared to your insurer. This is called ‘remapping’, and it involves overwriting the ECU’s default settings with new software to improve the car’s performance. After remapping, the car should be faster and more powerful, and the engine may be more responsive. You may also find you don’t need to change gear as frequently, providing you with better fuel economy.


Bodywork can include spoilers, flared wings, side skirts, wheel arches, valances, tinted windows, or changes to lights. These changes can affect the value of your car, its performance, and therefore the cost of your insurance. For example, spoilers can make your car go faster and increase the risk of an accident.

Brakes and Suspension

If the suspension has been modified or the car is fitted with uprated brakes, this can change the handling of your car and needs to be declared. Most commonly a car’s suspension is lowered, to improve handling and aerodynamics to give the driver a smoother ride.

Car Interior

Removing and replacing seats can change the weight and handling of your car. Changes to the pedals or the steering wheel also need to be declared. While some motorists may favour racing style interiors such as smaller steering wheels and bucket seats, these modifications can result in higher premiums. Even with smaller changes such as changing the knob on your gear stick, it’s better to be safe than sorry, so let your insurer know about the change even if you don’t think it’s significant.

Car Stickers

Even specialist paint, stickers, and decals – including stripes or badges – are considered to be a type of car modification, so check with your insurance provider to see if these changes will affect your policy.

Modifications With Increased Theft Risk

Fitted some shiny new alloy wheels, or wider tyres? This could increase the value of your car, as well as alter its handling, and it needs to be declared. Installing gadgets such as satnavs, DVD players and phone kits are also considered to be modifications as these carry a high theft risk. DVD players must also be installed in a position where the driver cannot see them to avoid distraction.

Modifications That May Positively Affect Your Premiums

Changes that improve the security of your car, such as immobilisers, could affect your insurance policy for the better, so declare these and you may benefit from lower insurance costs. Parking sensors could also lower your premiums as they mean you’ll be less likely to have an accident while reversing. Winter tyres will not positively or negatively impact your insurance, but you should still declare them to your insurer.

Modifications that may reduce your insurance premiums include:

  • Car alarm
  • Immobiliser
  • Black box tracking device (telematics)
  • Parking sensors
  • Tow bar

Changes To Your Car’s Handling

Insurance isn’t the only thing you should think about when considering making changes to your car. Modifications affect your insurance premiums for a reason – if your insurer thinks a modification will increase risk, you need to think about it, too. Will your modifications change the handling or performance of your car, and are you prepared to deal with that? And perhaps most importantly, are the modifications legal?

Police Crackdown On ‘Boy Racer’ Car Modifications

Car modifications are also very much a legal matter. In July 2016 it was reported that traffic officers in Birmingham seized over 60 modified cars in the area, in a crackdown on illegal street racing and the uninsured modifications associated with this activity. Some of the modifications would not have been covered by insurance due to safety issues – including changes to seats, suspension, steering wheels, brakes, and seat belts – while others would have significantly increased the drivers’ premiums.

Meanwhile on a lighter note, the Devon and Cornwall Police recently weighed in when a member of the public enquired about the legalities of fitting a flux capacitor to his vehicle.

Illegal Car Modifications

So what types of car modifications are illegal? Here are the modifications you’ll need to avoid in order to stay on the right side of the law:

Stretched Tyres

It is illegal to have stretched tyres on your vehicle as these make your vehicle unsafe to drive. Tyres should be fitted on suitable wheels and valves, and they should not be used on the road if they are not fit for use.

Custom Number Plates

Number plates must be white on the front of the vehicle and yellow on the rear, with black characters, unless the vehicle was registered before 31st December 1972 – in which case the number plate can be silver. The size, spacing, font or characters cannot be changed, and the plate cannot feature anything except for the characters and a national identifier.

Loud Music

Playing your music too loudly from your car stereo can lead to getting an ASBO which can ban you from certain roads, and you could even have your vehicle seized or your audio equipment confiscated. If you don’t want to get into trouble (or annoy your neighbours and other drivers), you might want to rethink that new subwoofer.

Large Exhausts

Many large exhausts are illegal for use on public roads – these are usually designed to increase the engine sound, and can be a public nuisance. The police do not have to measure the noise levels; they just need to believe that the system is noisier than other non-modified vehicles with the same specification.

Heavily Tinted Windows

Tinted windows are fine as long as they allow 70% of light through (75% for the windscreen). Windows found to be too heavily tinted could be considered dangerous, and you won’t be able to use the vehicle until this modification is rectified.

Coloured Lights

Have you ever been driving and noticed blue lights behind you? These may for a moment have made you think that there is an emergency vehicle trying to get past, until you take a second look and realise it is a normal vehicle with modified lights. Although these may be a nuisance, they are perfectly legal in some situations.

Blue lights must not be flashing or moving, and steady lights are allowed as long as they cannot be seen from the rear, are not fitted to your side lights, and do not dazzle other drivers.

Green lights can only be fitted on medical practitioners’ vehicles, while you are not allowed to show a red light to the front of a vehicle or a white light on the rear unless reversing.

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Be Wiser’s Guide to Car Modification