Yes, our custom car magnets adhere to most cars. Depending on conditions they can last 2 - 3 years.
However, we recommend sizes 102 mm x 102 mm or larger for outdoor use. Smaller magnets sometimes have trouble adhering due to the small surface area.
Please note, for use on vehicles to guard against moisture and dirt buildup between the magnet and the metal surface (particularly on outdoor applications), the magnet needs to be removed at regular intervals. Clean both the magnet and metal surface with mild detergent; wipe with a soft cloth or allow to air-dry. (For vehicle-mounted signs, remove and clean DAILY.)