Yes, a roof top tent has a negative effect on the fuel consumption of your car. If you mount a roof rack tent on the roof of your car you will find that the gasoline consumption of your car will increase. Especially when you are traveling at higher speed, for example when you are driving at higher speed on the highway. This is because the aerodynamics of your car is disturbed by the additional structure on the roof of your car. Normally the airflow moves cleanly over your car and the car roof, but when the roof tent is installed this airflow is blocked and no longer ideally directed over the car. This creates higher wind resistance, which at the same time leads to increased fuel consumption.
What can you do about the higher fuel consumption?
If you don’t need the roof rack tent and are not going camping, you should dismantle the tent and store it safely in your garage. But if you don’t want to dismantle the roof tent or want to go camping with your roof tent again the next weekend, you shouldn’t drive so fast in the meantime, for example when you’re on the highway.
Make sure that the roof tent is properly packed and that no parts protrude, such as poles or the tent skin. You can also put an extra tarpaulin over the tent to reduce the air resistance, but that won’t help very much either. The only thing that really helps is if you remove the roof top tent if you don’t absolutely need it to restore the aerodynamics of your vehicle.
