Before deciding to go ahead with modifying your car you should be aware that even the slightest alteration could invalidate your insurance if you fail to declare it.

Car owners should always tell insurers about modifications made to their car, as failing to declare your modifications could invalidate your policy. If you have already taken a policy out and decide to make alterations to your car, you must inform your insurance company as soon as you do so. Do not wait until it is time to renew.

Insurance providers are able to calculate how modifications can change insurance policies through assessing the risk of accident, risk of theft and value of the vehicle. Modifications that include engine changes, sports seats, spoilers etc. can also alter the performance of vehicles. It is down to your personal preference on whether shiny new wheels are worth more than the safety of you and those surrounding you. Modified vehicles will become more valuable as the changes made do not come cheap, meaning insurers will tend to charge more to insure vehicles which will cost more to replace or repair if they are involved in an accident.

Even paint jobs can lead to car owners paying more for cover, as some insurers link specialist paint, decals, stripes and rally numbers to a higher risk of theft.

The most expensive areas where modifications can be made on your car are the engine and mechanics, bodywork, and interior. Motorists who decide to add a turbo/supercharging to the engine can expect a 91% increase on their insurance, and a transmission/gear change will inflict a 45% inflation. Implementing wheel arches (41%) onto the car's bodywork will will see the third highest increase in insurance costs.

Although most modifications made to vehicles will see an increase in cost of insurance cover, there are a few changes that will see you save money. Additions of parking sensors (-13%), tow bars (-8%) and accessibility modifications (-2%) will see a decrease in premiums as these changes will reduce the risk of damage. A sunroof and air conditioning would both see a insurance premium decrease of -1%.

It is also worth noting that not all car modifications are legal, and failing to comply with the laws could result in you being prosecuted, on top of your car insurance policy being invalidated. Illegal car modifications include tinted windows, as the car windscreen must let in a minimum of 75% light and front side windows must let in 70%. Also, when modifying number plates you must use the correct font and spacing.

With more and more modified vehicles on the road, it is also worth knowing how to tell if one has undergone expensive surgery. If you haven't already noticed the shiny rims and huge exhausts, always make sure to ask the owner if any modifications have been made. Common car upgrades include bigger wheels, alloy wheels, tinted windows, adjusted suspension, sports exhausts, spoilers, and upgraded stereo systems.

If you are cautious that any of the above modifications are not 'factory-fitted', you should refer to the vehicles specifications that can be found online via car buying websites e.g.

For full details on how vehicle modifications can change the price you pay for car insurance please see the guide below.

How is car insurance affected  by modifications?

Engine and mechanics

  • Turbo/Supercharging                                                                                                                                           91% increase
  • Transmission/Gear change                                                                                                                                 45% increase
  • Exhaust changes                                                                                                                                                      3% increase


  • Wheel arches                                                                                                                                                            41% increase
  • Complete body kit                                                                                                                                                   26% increase
  • Spoilers                                                                                                                                                                        7% increase
  • Light changes                                                                                                                                                             6% increase
  • Tinted windows                                                                                                                                                          1% increase
  • Tow bar                                                                                                                                                                        8% decrease
  • Accessibility modifications                                                                                                                                      2% decrease


  • Replacement of seats                                                                                                                                              16% increase
  • Replacement of steering wheel                                                                                                                             16% increase
  • Dashboard changes                                                                                                                                                   3% increase

Brakes and suspension

  • Uprated brakes                                                                                                                                                         15% increase
  • Suspension                                                                                                                                                                  2% increase


  • Specialised paintwork                                                                                                                                              15% increase
  • Stripes and badges                                                                                                                                                      9% increase


  • Alloy wheels                                                                                                                                                                  1% increase

Fuel economy

  • LPG conversion                                                                                                                                                               no change

Driver aids

  • Satellite navigation system                                                                                                                                       13% increase
  • Car phone kit                                                                                                                                                               12% increase
  • Parking sensors                                                                                                                                                           13% decrease




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