Car modifications: the ultimate guide

Jump to
Cosmetic vs performance
Modifications and price
Tell your insurer
Buying a modified car
Inform the DVLA
Modification types
Security upgrades
Illegal modifications
Winter tyres
Younger drivers
Modifications for disabilities
Cheaper insurance

Eyeing up that sunroof, decal or wheel lock but worried what it might do to your premium?

Car modifications usually make insurance more expensive because they increase the value of a vehicle.

Some changes, however, could make a car policy cheaper if they make a car more secure.

Here's everything you need to know. 👇

Car modifications include most changes made to your car

Most changes that make your vehicle look and drive differently from how it was originally manufactured are classed as car modifications.

This includes alterations or upgrades offered by dealers when you buy a new car.

Car modifications are split into two main categories:

Cosmetic Modifications

These change the appearance of a car, for example by changing the car colour with a custom paint job or tinting the windows.

Performance modifications

These are changes that make a car drive differently, for example by installing a bigger engine.

Car modifications can make insurance more expensive

Insurance tends to be more expensive if you have a modified car because, statistically, drivers that alter their vehicles make more claims.

The modifications don't necessarily need to be dangerous or risky to impact your policy price.

Most modifications also affect the value of your car. Custom parts are usually more expensive to repair or replace, which means insurers need to factor this in when thinking about your price.

Performance alterations like changes to your engine, brakes or exhaust can also affect the insurance group your car is in.

Every car in the UK is put into one of 50 insurance groups that insurers use, along with a few other things, to calculate how much you pay for a policy.

As a general rule, the higher your insurance group, the more it adds to the cost of your car insurance. (Pssst: you can [check your car's insurance group here](insurance group).)

Performance modifications also tend to increase the cost of car insurance more because they increase your risk of getting into an accident.

Cosmetic changes like a custom paint job could also make it more likely to get stolen.

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Telling your insurer about car modifications

You should tell your insurer about any car modifications before applying for a policy, as some companies won't insure them.

Your policy could be invalidated if you don't declare the modifications, which means your insurer wouldn't pay out if you have to make a claim. 🚫

It's really important that you speak to your insurer before modifying a car to make sure that the changes can be covered by your existing policy.

If they're able to insure the modifications you want, your policy price could increase and there may be an admin fee to update your details too.

If they won't insure it, and you go ahead with the modifictions anyway, your policy will probably be cancelled, which could make it harder and more expensive to find insurance in the future. Not a good idea!

Buying a modified car

It's important to check the following features before buying a modified car:

Quality of the modified parts and fittings

It's important to check that the modified parts are from trusted industry brands to guarantee their quality. Take the car for a test drive to make sure the parts work properly. It's also worth asking the seller for evidence to certify that the modifications were fitted by a reputable company or service.

General state of the car

It's worth checking the service history and MOT records to gauge a car's condition. Our free car checker shows everything you need to know about a car including its:

Check the modifications are legal

Some car modifications are illegal as they make cars more dangerous on the road. For example, bright under-car neon lighting. Insurers won't cover illegal modifications and you might get a fine (or even go to court) if you're driving with them.

Car modifications can make your car safer
Car modifications can make your car safer

Your DVLA records need to be updated if you get car modifications

The Driver and Vehicle Licensing Agency (DVLA) needs accurate records of your car's details for tax and road safety purposes.

Insurance companies and the police use DVLA records to get information about your car, including the colour, model and engine size.

You can look at that data for free using our car checker tool.

You'll also need to contact the DVLA to update your vehicle details if you make certain modifications to your car.

This includes changing the:

  • Colour
  • Engine
  • Cylinder capacity (cc)
  • Fuel type
  • Chassis or bodyshell (replaced or modified)
  • Number of seats
  • Weight of a large vehicle, for example a goods vehicle or campervan

To make any changes, you'll need to update something called a V5C (also known as a "log book"), which is the paperwork you get from the DVLA to prove that you're the registered keeper of a car.

You'll need to complete section 7 of the V5C and send it off to DVLA, Swansea, SA99 1BA.

A new V5C should be sent to you within two to four weeks.

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Types of car modification

Common types of car modification could make your policy expensive such as:

Engine or mechanical modifications

Upgrading to a bigger engine makes a vehicle drive faster and more likely to get into an accident. It also increases the value of your car, making it more expensive to insure.

Wheels and alloys upgrades

Opting for bigger wheels and new shiny alloy can change the way a car drives and make it more likely to get stolen.

Exhaust modifications

Exhaust upgrades give cars a boost in speed, making them less safe on roads and more expensive to insure.

Cosmetic changes

Custom paint jobs, vinyl wraps or resprays to change your car colour and bumper stickers could make your car more valuable and increase the chance of it being targeted by thieves.

External modifications

Adding features like a sunroof, a tow bar or a roof rack are also classed as modifications that could increase your car policy price.

Bodywork modifications

Body kits, which include things like bigger bumpers and side skirts, aren't usually designed with safety in mind and are more likely to get damaged in an accident.

Sound and entertainment upgrades

Upgrading your sound system and installing in-car entertainment increases the value of your car, making it more likely to get stolen or damaged. They're also more expensive to repair if anything gets damaged.

Number plates

Some insurers consider personalised number plates to be car modifications, and they could increase the price of your premium.

Car modifications can make driving more fun
Car modifications like sat-navs can open the road/b>

Security upgrades could make your insurance cheaper

Some car modifications could make your policy cheaper if they improve the security of your vehicle.

This includes installing things like:

  • Car alarms
  • Electronic immobilisers
  • Parking sensors
  • Dash cams
  • Locking wheel devices
  • Vehicle tracking devices

Most insurance companies approve of devices endorsed by Thatcham, an independent organisation that rates car security.

You can ask your insurer about the discounts available for adding certain security features to your car.

Car modifications and the law

Certain car modifications are illegal because they make vehicles unsafe to be on the road.

These include:

  • Tinted windows that restrict more than 70% light
  • Bright under car neon lights
  • Nitrous oxide engine modifications
  • Sound and noise modifiers

Illegal car modifications could land you with a penalty and in some cases court action. 😬

Your insurer may also cancel your policy. If you get into an accident and have to make a claim, you might not get a payout.

Winter tyres aren't considered modifications anymore

Most insurers signed an agreement to take winter tyres off the car modifications list, so using them shouldn't affect your policy price.

A handful of insurers still need you to tell them if you use winter tyres even though it won't increase your premium. Always check, just in case.

Younger drivers be cautious with certain car modifications

Performance and cosmetic car modifications usually drive up the cost of a car policy, which can make it very expensive for younger drivers to get insurance.

Drivers under 25 already pay the most for car insurance because they tend to have more accidents and make more claims.

So if you're a younger driver or already have an expensive car premium, avoiding performance or cosmetic car modifications can help you pay less for a policy.

Instead, consider car modifications that boost your car's safety and security. This will reduce your risk of needing to claim and could make your policy cheaper.

Car modifications for physical disabilities

If your car needs to be adapted to suit a physical disability, you'll need to tell your insurer about the changes and your policy could get more expensive too.

These include installing:

  • Ramps
  • Tail lifts
  • Transfer seats
  • Wheelchair storage
  • Handbrake adaption
  • Infra-red controls

Some insurance companies offer tailored policies if you have a physical disability.

Cut the cost of insurance if your car is modified

The cost of insurance for cars with performance or cosmetic modifications is usually more expensive.

Keeping your annual mileage low can help make your policy cheaper though.

Where possible, paying annually for car cover can cut the cost of a policy and avoid them adding interest to your payment.

Some insurance companies offer insurance designed for modified cars. These might be a cheaper than a standard policy.

Cuvva allows a huge range of modifications, including those designed to improve your security or help you if you suffer from any disabilities.

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Updated on 30th March 2023