Have you been contemplating making some upgrades to your car - maybe thought about fitting a big rear spoiler, a louder exhaust or even just a racing stripe?
All of these additions might improve the performance or change the look of your vehicle but some can more than double the price of your insurance.
That's according to new research by MoneySuperMarket, which has listed the vehicle modifications that have the biggest impact on insurance costs, with some spiking premiums by as much as 132 per cent.
But it's not just bonnet bulges, massive wheels and souped-up engines you need to worry about, not telling a provider about all kinds of modifications - even changing the paint colour or having a sat-nav fitted - could invalidate your policy, the price comparison site warned.
Of all the changes you could make to your car, fitting a more powerful engine is the one that will see your insurance premiums sky rocket most.
After reviewing 2.3 million quotes for modified vehicles, MoneySuperMarket found fitting a turbo engine will increase the cost of insurance by an eye-watering 132 per cent.
But even purely aesthetic changes can have an impact on how much your cover costs.
Upgrading the bodywork with a bonnet bulge, flared wings or wheel arches can result in your premiums shooting up by an average of 66 per cent.
According to the research, even adding stripes or badges can cause a 22 per cent cost surge.
But it's not just performance and aesthetic upgrades that can have an affect - even small additions to a car, such as a sat-nav, can have an impact on how much insurance you pay, as Kevin Pratt, consumer affairs expert at MoneySuperMarket, explained.
'Modifications can be a great way to personalise a car and in some instances will improve performance, but can quickly bump up the cost of your car insurance,' he said.
'Insurance is based on risk, and modifying your car is a warning sign to insurers.
'For example, spoilers or turbo engines will mean a vehicle goes faster, and therefore increase the likelihood of an accident, while car phones and sat-navs are attractive to opportunistic thieves, so insurers balance the scales by pushing premiums up.
'When you change anything about your car, you change the original specification which may invalidate your policy if you don’t inform your insurer.
'Reporting the changes might mean a higher premium, but having an invalid policy is considered fraudulent and could reduce or even remove the prospect of a pay-out if you had to make a claim.'
TOP 10 MODIFICATIONS THAT CAN INCREASE THE COST OF PREMIUMS:
1. Fitting a turbo engine: 132% rise
2. Change to car bodywork: 66% rise
3. Transmission or gearing changes: 63% rise
4. A complete body kit and panel: 57% rise
5. Roll bars, roll cages and the removal of seats: 41% rise