I remember watching Nat Geo featuring Dr. Brady Barr doing bite force tests on all types of animals, including dogs. The dogs that were tested were the Rottweiler, German Shep, and an American Pit bull Terrier. The results may surprise you.
Domestic dogs: 320 LBS of pressure on avg. A German Shepherd Dog, American Pit Bull Terrier (APBT), and Rottweiler were tested using a bite sleeve equipped with a specialized computer instrument. The APBT had the least amount of pressure of the 3 dogs tested.