Big SUVs and trucks require proper tire inflation because the tires are expected to carry heavy loads. Trucks and SUVs are typically heavier than common passenger vehicles. Furthermore, they have been designed to carry loads in addition to passengers. This means that the tires will have to endure considerably more weight. The most important factor for inflating these types of tires is adhering to the tire manufacturer’s specifications for tire pressure, molded into the side of the tire. This ensures that the tires will be able to handle the load(s), and perform correctly while doing so.
For more info, see Tips for Properly Inflating Tires