Car Modifications - Are They Legal?

Take a short drive down most UK streets and it won't take long to see a number of cars with various modifications. From supersized exhausts to tinted windows and rear spoilers, there is a huge market for car modification parts and many drivers see it as a chance to customise their pride and joy. But before you close this tab and begin searching for BMW MINI performance parts or modifications for whichever type of car you drive, it's important to understand that not all car modifications are legal, and if you want to avoid costly fines or in extreme cases even a court summons, then you'll want to ensure that your modifications stay on the right side of the law. 

What is classed as a car modification?

A car modification is defined as any alteration that sits outside of the car manufacturer's intended specification - this could be changing the tint on the windows, adding a spoiler, changing the exhaust, fitting an upgraded sound system, or altering the suspension by changing the shock absorbers. Accordingly, if you are considering investing in new shock absorbers car part websites are a fantastic resource as you will be able to compare products and prices to find the best parts for your needs and budget. That is not all though. Not all car modifications dramatically change the look of the vehicle, and so if you are buying a second-hand car it's important to ask the previous owner if there are any modifications as undeclared modifications can cause your insurance to be void. 

Are car modifications legal?

When it comes to what is legal and what is not, there are definitely some grey areas when it comes to car modifications, and so it's always best to air on the side of caution. Here are some of the most common types of car modification and the things to watch out for. 


Spoilers instantly give a car a more sporty feel but if fitted incorrectly can endanger other road users. Spoilers themselves are not illegal, but in order to pass an MOT and to remain on the right side of the law, you must ensure that they are fitted correctly, cannot detach during driving, do not obstruct the driver's rear vision and do not have any overly sharp edges. 


Upgrading your exhaust to enhance the noise of your engine can land you with an on the spot fine. To a certain extent what a police officer classes as 'noisy' can be subjective, but in general, the legal noise limit is about 82 decibels and the exhaust must not hinder the performance of the car. You may also want to add a turbo to your exhaust, just be aware that in order to be legal the car will need to pass an MOT emissions test. 

Tinted Windows

There are no limitations to how dark the rear side windows and rear windscreen of your car can be, but the windscreen and front side windows are another matter. The front windows must let at least 70% light through and the windscreen must let a minimum of 75%. Driving with illegal tints will get you pulled over by the police and they'll likely seize your car until the tints are removed. 

Lowered Suspension & Subwoofers

Lowering the suspension of your car or installing a subwoofer is not illegal but if don't incorrectly or to an extreme then they can hinder your car's performance. Lowered suspension can make it difficult to go over speed bumps and a significant sound system can cause weight distribution issues in the back of the car. 


So are car modifications illegal? The answer is no - so long as you are sensible and don't push the limits of the law too far.