When you have a roof rack installed on your car, you're giving your car a break and reducing the chances of it sustaining damage. When you try to pack the inside of the car with oversized items or hang things off a rack on the boot of the car, you risk scratching the paint or the upholstery, and if you didn't install that boot rack correctly, you could end up with dents in your car from things like bicycle wheels that aren't properly secured. A roof rack provides a secure storage place for these items as you drive, but you will have to adjust your driving and car-care habits.
Your Car's Height
Even when you don't have anything secured on the rack, your car's height will change. The rack connections themselves will add a bit to the height of the vehicle, depending on the style that you get. Flush rails, for example, really don't add anything when you don't have the rest of the rack attached, but raised rails do. For smaller cars, this doesn't mean much, but for vehicles with taller profiles, those few centimetres can affect how your vehicle fits in garages and under low overpasses, tree branches, and so on. You must make sure that you know the height of your vehicle as a whole when you have an empty rack attached, as well as when you have items secured to the rack.
It's Not Just Automatic Car Washes You Have to Prepare For
You should not take a fully assembled and installed car rack through an automatic car wash; if you want to go through one, park the car for a minute and remove the main rack. But it's not just the automatic washes that are a risk. Any car wash you go through, even one where you pay to hose down the car yourself, can be more difficult with the rack fully installed. This doesn't refer to the permanently installed connection points or rails, but to the crossbars and racks that you can remove. When the full rack is on, you may not be able to get all the dirt off the roof, and you may find soapy water continuing to drip out of the rack as you drive away from the car wash. In car washes where an employee drives your car through the washing portion, you can end up with bristles and bits of cloth stuck in the rack.
Cornering and Handling With a Full Rack
Remember that when you move your bike and other equipment from the boot of the car to the roof, you change the centre of gravity, and your car will handle differently. Going around a corner will change, and you don't want to risk not being able to brake in time because you overloaded your car and didn't do a few test braking sessions first. When you add items to the rack, drive slowly and carefully for a bit to get used to how the car handles and how much braking time it will require.
You've got a choice between several styles of roof racks; what your vehicle already has installed on its roof will influence the choice somewhat, but you'll still have options. Speak with a seller to find out which racks will fit your car.