Greyhounds can reach a speed of up to 45 miles per hour. Greyhounds can beat cheetahs in a race. While cheetahs can run twice as fast as greyhounds, they can only maintain that 70 mph speed for about thirty seconds. A Greyhound can maintain a 35 mph speed for about seven miles. So, the cheetah may start out first, but the greyhound will soon overtake him. A 2008 University of Pennsylvania study found that Greyhounds are one of the least aggressive dog breeds towards strangers, owners, and other dogs.