Very little if you put your luggage inside an aerodynamic, rigid storage box like the ones offered by Thule. These spacious, low profile cargo ‘pods’ offer protection from the elements, secure lockable storage, and practically no impact on your fuel mileage. They attach to you vehicle’s stock roof rack quickly and easily. Best of all, Thule pods come in a wide range of sizes to accommodate any size family or vehicle, and they’re available from Alamo!