Most modifications will have an effect on the premium you pay. Usually, they result in a small lift in your premium, although some could see the amount you pay go down. Among the modifications that could have a negative impact on what you pay are: Alloy wheels Window tints Bespoke paint jobs Spoilers … and eyelashes on headlights! Among the modifications that could have a positive impact on what you pay are: Having an immobiliser fitted Having a tracker fitted Having a tow bar fitted (caravans slow you down) Upgraded braking system You must tell your insurer if you’ve had any modifications done to your car or any non-factory fitted mods had been added before you purchased the car.