What’s so bad about car modifications?

Generally, ‘modifications’ are any changes that weren’t part of the original manufacturer spec, like non-standard alloys or tinted windows.

You need to know whether or not your car has been modified as it can make your insurance more expensive, or even invalidate it. This is for several reasons:

  • Modded cars may be attractive to thieves and vandals
  • Botched DIY projects may make the car dangerous to drive
  • Enhancements to performance could mean more damage in a crash
  • Replacing specialist parts could be difficult and expensive

These problems mean that many insurers (including ingenie) don’t insure modified cars for young drivers.

But it’s not just about insurance – modifications can cause all sorts of other problems, from driving up your fuel costs to actually breaking the law.

Why modifications are not as cool as they look

Fuel economy:

Because they’re heavy, bigger wheels will affect your fuel economy. You might like the way they look, but you won’t like the extra fuel costs!

A sports exhaust will have the same effect – you’ll get that boy racer POP but your car’s actual performance will probably be decreased.

Ride and handling:

Bigger wheels can also affect how comfortably your car deals with our awful British roads, and how easy it is for you to control it. Since many are fitted with low profile tyres, they’re more likely to get punctures too.

Noise and emissions:

Sports exhausts don’t only affect fuel economy – they may also breach noise and harmful emission levels, resulting in an MOT fail.


Upgraded stereos may give you a banging sound but they’ll also make your car more attractive to thieves, and your car probably won’t have the security to match. They can also cause electrical problems if they haven’t been fitted correctly.


We often get asked why tinted windows affect insurance, and the reason that most insurers (including ingenie) won’t cover cars with this modification is that they can break the law as well as potentially being unsafe.

Tinted windows can significantly restrict your vision while driving, so by law they must let in at least 70% of light. However, with DIY tint sets and unfussy installers making unsafe tinting possible, many insurers steer clear of them altogether.

How to tell if a car has modifications

It’s not always easy to tell whether a previous owner has made changes to your car but here are a few tips:

  1. The obvious way to find out about mods is to ask the person you bought it from – not always easy!
  2. The most common modifications to look out for are:
    • Bigger wheels
    • Adjusted suspension
    • Alloy wheels
    • Spoilers
    • Tinted windows
    • Sports exhausts
    • Upgraded stereos

  1. If you’re shopping around for your first car, you’re probably looking for something on the small side. Small cars aren’t generally manufactured with large wheels or sports exhausts so any modifications may stick out.
  2. If you’re still not sure, Google the exact spec and year of the car – does your car look different?
  3. Failing that, check the manufacturer’s website or even drop in to a dealership and ask for help.

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