I've witnessed the results of several people applying too much pressure in their rear tractor tires. Avoid this mistake yourself! Let's discuss the proper type of gauge to use, and also how much pressure to put into your tire on this video:
A general rule to follow is one pound of pressure per cross section on your tire. The 12.4x28 tire on my Ford Jubilee needs approximately 12 pounds of pressure. Of course, the recommended pressure may slightly change based on your current usage or load.