car modifications: laws and regulations explained

There are two categories of car modification: cosmetic and performance. Cosmetic modifications are all to do with the appearance of your vehicle, whereas performance modifications affect how it runs.

In most cases, car modifications are legal, but within limitations and subject to certain conditions. In our car modifications list below, we outline the necessary requirements for some of the most popular car modifications.

Cosmetic modifications

Tinted windows

Tinted windows are legal, and a common modification for both privacy and that edgy look. There are, however, some legal requirements for this: if you’re going to tint your car’s windows, the front side windows must still let through at least 70% of light. For a legal front window tint, the windscreen still needs to let in 75% of light as an absolute minimum.

If your car was registered before 1985, however, the front side windows need to be 75% tint-free, too. If you add tinted windows to your car, it’s illegal for them to be too dark.

Car wrapping/painting

A sure-fire way to make your car stand out, it’s perfectly legal to change the colour of your car. This can be done in the form of a spray, or as a vinyl film that is printed and wrapped onto the vehicle.

As with many legal car modifications, the main condition here is that if you change the colour of your car to something other than what is on your official V5C, you need to record it with your insurer and the DVSA.

 Lowered suspension

This brings the body of your car lower to the ground. It’s crucial to make sure that if you do lower your car’s suspension, you have it done by a professional. That’s because, if not done correctly, this modification could cause your car to fail its MOT.

It’s worth bearing in mind that a lower suspension will also change the way that you drive; this change isn’t just cosmetic. Namely, it will reduce your ground clearance, making speedbumps, potholes or kerbs a bigger issue, as well as affecting the handling of the car itself.

Spoilers

In theory, spoilers improve the handling and performance of a car. However, most people add one as an aesthetic feature to imply sport.

Adding a spoiler is completely legal and harmless. It needs to be securely fixed, with no sharp edges, and without blocking your rear view. As long as those criteria are met, adding a spoiler to your car is absolutely fine.

Alloy wheels

Alloy wheels are one of the most popular types of car modification, if not the most popular. That’s because it’s a simple way of customising and personalising your car without hugely affecting the way it drives.

They’re actually slightly lighter than standard wheels, which therefore limits wear and tear on the engine, transmission, and more. They can also contribute to better braking as they’re better at staying cool due to the material. In turn, this minimised heat can also make your tyres last longer. Plus, alloys look great, right?

Performance modifications

Engine swapping

Engine swapping is sometimes used in older cars to get them back up and running if its old engine has failed. However, it’s also sometimes used to modify a car, usually to make it more powerful.

If you’re swapping your car’s engine out for a different one, rather than a like-for-like exchange, you’ll need to make further modifications to your vehicle in order to make it work. You’ll also have to inform your insurer and the DVSA.

Exhaust modifications

Generally, large bore exhausts are designed and fitted to your car to make it sound like its engine is more powerful than it actually is; but when it comes to exhaust modifications, like with engines, it gets a bit more complicated than a simple swap.

That’s because what you’re allowed to do depends on your vehicle category. As long as it doesn’t make your car louder than its type approval allows for, you should be okay in modifying the exhaust. However, you should do your research beforehand and find out what that limit is for your car.

Can you modify a car bought on finance?

If you’re looking to modify a car you’re paying for on finance, you may need to get written permission from the finance provider, so always check with them first before making any changes

If you have a personal contract purchase (PCP), you don’t outright own your car, so you won’t be able to make any significant changes to it. If you do alter your car without permission and this affects its resale value, your finance company could reclaim the car from you.

Will modifying my car affect my insurance?

Modifying your car is likely to affect your insurance cost. Cosmetic changes are intended to increase the desirability of your vehicle, so they could increase the likelihood of your car being stolen. Performance tweaks, on the other hand, are sometimes seen by insurance providers as a higher accident risk.

However, how much your premium is affected depends on which modifications you make. It also ultimately depends on the provider too, so it’s always worth consulting with them before making any amends to your vehicle.

When it comes to vehicle modifications, DVLA and insurance notification is the most important part to make sure the change is legally registered.

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