How a new roof rack, alloy wheels or even a satnav can drive up your car insurance

Most drivers would expect “boy racer” car modifications to increase their insurance premiums. But even those motorists who roll their eyes at the thought of adding tinted windows and loud speakers to their car could still fall foul of insurers’ rules around modifications.

Even the most genteel additions,

such as roof racks and satnavs, can bump up insurance costs. This is because changing a car in any way might increase its value, how it handles or how likely it is to be stolen.

For example, adding alloy wheels or leather seats might raise the vehicle’s worth. Insurers are left out of pocket when paying claims for cars modified after buying cover, as it would have been insured at a price lower than the cost of having to repair or replace it.

Aside from increasing the car’s value, additions such as alloy wheels will increase premiums because they are easily, and often, stolen. If drivers live in an area where this theft is common, their cover costs may increase. How much a roof rack can add to your premiums

Some modifications, such as bigger engines, new wheels and spoilers, can affect how cars handle. If insurers think these changes will increase the chance of accidents, premiums will rise.

Adding alloy wheels can increase insurance for a Vauxhall Corsa from £927 a year to £974. Putting a roof rack on a Volvo V70 estate can drive up its insurance from £983 to £1,019. Adding either a satnav or electronic sensors to help with parking will raise premiums to £993, while a tow bar will increase these costs to £1,010.

To save money, it is tempting not to mention modifications to insurers, but doing so might mean the firms reject claims.