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Modifying your car: UK laws, insurance and tips

Modified cars look super cool in movies but in real life, they can be illegal. Find out more about legal and illegal modifications in the UK, buying a customised car and insuring it.

What is car modification?

Car modification, also known as car tuning or car styling, involves changing the car so that it no longer matches the manufacturer’s original specifications.
Car modification could involve adding car parts, such as performance-enhancing brakes, steering and suspension to tune the car’s performance. Car modification could also focus on aesthetics, for example changing the car’s colour, headlights or grille. Car modification should not be confused with repairing a car. A car repair replaces the damaged car part with an identical one or fixes it to maintain the car as per factory standards. Car modification is done for the sake of customising your car, to make it look more stylish or to enhance handling and performance using bespoke car parts.

Types of car modification

There are two main types of car modifications:
1. Cosmetic modification 2. Performance modification These modifications can be achieved in a couple of ways. The most common modifications include increasing horsepower, tinting windows or lights, adding alloy wheels, spoilers, exhausts or engine chrome covers, or making customisations to interiors and bodywork.

1. Cosmetic modification

Changes made to the car purely for its looks and aesthetics are classified under cosmetic modifications. Cosmetic modifications can include changes to:
• Body kit • Front and rear bumpers • Rooftop vents • Paintwork • Wheel accessories • Interior LED lighting • Light lens tints • Tinted windscreens • Back bumper reflector lights • Custom hood ornament • Dashboard customisation These are some great ways of making your car stand out in the crowd. You could choose from a simple paint job to give your car a distinctive colour, or go all in and get a number of different customisations to make your car uniquely yours. What are xenon and LED car lights?

2. Performance modification

Performance modifications help improve the handling, fuel efficiency, power, and speed of the car. Some common areas of upgrades are:
1. Brakes 2. Engine and drivetrain 3. Exhaust 4. Suspension 5. Steering 6. Filtration These modifications change your car subtly – you’ll feel your car’s improved overall speed and performance while the car will continue to look the same as others.

What car modifications are illegal in the UK?

Some car modifications are illegal in the UK because they can be unsafe for the driver and others around them. You can be at risk of a fine if you make these modifications to your car, which is why it’s important to keep the law in mind before getting any changes to your vehicle.
Some common car modifications that are illegal in the UK are:

1. Neon Lights

Neon light modifications are illegal in most scenarios. One of the few ways you can legally spruce up your car with neon lights is if you add them to the bottom of your car – but only if the neon tubing isn’t visible, and the light isn’t too bright or flashy that it distracts other drivers around you.

2. Rear and headlight tints

In the UK, white and yellow lights are allowed at the front, while red lights are allowed for the back of the car. Using red, green or purple tints for your headlights, or any bright neon or flashy lights on the exterior or interior of the car, are sure to get you pulled over. Any halogen bulbs with a colour temperature over 4,200 K are not road legal as they produce a slight blue tint light. Blue flashing lights are used by emergency services such as police vehicles, ambulances, firefighters, and the coastguard. To make these services stand-out, these lights are legal only for emergency service vehicles. Also, the lights shouldn’t be dimmed by more than 50% to maintain visibility. If the light bulbs bear an ECE R37 regulation, it’s a sign that the lights are road legal.

3. Window tints

You can tint your windows, but only to a certain degree. The front windscreen needs to be at least 75% tint-free and the side windows need to be minimum 70% tint-free to ensure a clear view of the surroundings. The only exception is if your vehicle was first put on the road before 1 April 1985. In this case, both the front and side windows need to be 75% tint-free. It’s illegal to sell a car that doesn’t follow these rules.

4. Loud exhausts

A loud, roaring car sure sounds thrilling, but the noise might irritate others. An exhaust cannot cross the noise limit of 74 decibels, so any modifications that breach this limit are illegal. All cars are ‘type approved’ under the Individual Vehicle Approval (IVA) scheme before they’re sold to you, which means that they comply with the emissions and safety regulations. Other exhaust modifications, like changes to the exhaust management system, tampering with the emissions control system, or removing some parts could make the vehicles more damaging to the environment.

5. Spoiler upgrades

Spoilers help with aerodynamic efficiency, and a slight tweak to their look can help improve handling and make the car look sportier. While modifying a spoiler isn’t illegal, the method of modification can be. If the new spoiler isn’t fastened safely to the car or has exposed sharp edges, you can get into trouble with the police and may even be forced to remove the modified spoiler. Spoiler modifications should help reduce your car’s drag and weight. A rear spoiler can improve the downforce, while front spoilers can reduce drag. The modification should also be a practical size so it doesn’t obstruct your view – three inches wide and six inches above the roofline spoilers are usually considered an efficient size.

6. Nitrous Oxide engine modification

The use of Nitrous Oxide is illegal and extremely dangerous. Adding Nitrous Oxide gas to your engine can increase cylinder pressure. If the engine’s components are unable to handle the increased stress, the engine can suffer damage. The engine can also be damaged when there’s too much oxygen and not enough fuel in the engine (an incorrect ratio of air and fuel). In the worst-case scenario, the incorrect ratio and added cylinder pressure could cause the engine to explode.

Does modifying cars affect insurance?

Even the slightest change to your car will have an impact on the insurance cost. Your insurance provider may think that increasing your car’s performance can mean a higher risk of accidents. Changing the appearance of your car to make head turns can also attract thieves, which could mean there’s a higher risk of your car getting stolen. In any case, a higher risk usually translates into a higher premium charged by insurance providers.
Once you’ve decided to get a car modification, you need to inform your car insurer about the changes, no matter how small they are. It might pinch to pay a higher premium because of the modifications, but it’s necessary as your insurance coverage can become invalid if you fail to inform them. If you need to make a claim or if someone files a claim against you and you haven’t informed the provider, you may not be eligible for compensation. Not all modifications lead to a rise in your premium. Some might bring down the total amount you pay, like engine downsizing or adding high-performance brakes.

Which modifications affect car insurance?

Modifications to your car can either bring down the insurance premium or increase it.
We’ve listed down some common changes that can affect the amount you pay. However, it’s best to consult your insurance provider first about how the modification will impact your premium.

Could increase your premium:

• Supercharger installation • Brake discs upgrades such as carbon-ceramic discs or drilled discs • Engine control unit (ECU) reprogramming to tune engine performance • Changing or adding another ECU chip to improve brake force • Body kits to improve safety • Exterior cosmetic modifications such as flared wings, wheel arches, spoilers, valances, paint jobs, tints, stripes and badges • Interior cosmetic modifications such as changes to upholstery, sat-nav system, dashboard, phone kits, air conditioning • Short shift kits • Cold air intake filter installation for increased power • Sunroof • Alloy wheels

Could decrease your premium:

• Adding technology like immobilisers, smart water and parking sensors • Anti-roll bars • Engine downsizing if it increases car efficiency • Improved braking system • Suspension upgrades if it improves handling

Buying a used car with modifications

Buying a customised car can have its pros and cons:


• Internal modifications could have improved performance • You can have a unique-looking car at a low or no extra cost • If you personally like modifications, then you get them without having spent any money or time on it


• The modifications might be damaging the car’s engine • Risk of the modifications not being done by a professional • Warranty might be void because of the modifications • The fitted parts might be low quality • Legality issues, as mentioned above If you’re considering buying a modified car, you should collect information like where the modification was done, which brand’s car parts were fitted, any mechanical issues and the value of the car after the modifications. Also ask for a service history of the car. Selling a car with modifications is allowed if the modifications are legal in the UK. It can be a good idea to retain the receipts for the modifications you buy. This shows the buyer where you got the modifications done and the quality of the parts used.

Can you modify a financed car?

Under a PCP car finance contract, you aren’t the legal owner of the car until you’ve paid the full amount. This means you can’t modify a car bought on finance unless you get written permission from your finance provider.
If you’re able to get permission for any modifications, it’s important that you only modify what has been agreed to in the contract. If you change anything that hasn’t been agreed upon, you’ll be in breach of the contract and may become liable to pay excessive penalties and fees or have your agreement terminated. it's also important to consider what your finance provider would consider being a modification. You might think that getting an upgraded stereo or sat-nav system or any temporary changes are not actually modifying the car, but your lender may think otherwise. In all instances, check with your finance provider before you start making modifications.

Tips for modifying your car

If you’re keen to modify your car, then here are some key points to get started:
• Find out how the modification will affect your car’s performance • Know if the modification can be reversed or not, and its cost • Keep in mind any risks associated with the modification • Go to a professional to get the changes done • Check if your intended modifications are legal • Inform your insurer and get a specialist car modification insurance Looking for something a bit different? On Auto Trader, you can easily search for modified cars.
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