 Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run ( no airborne phase in mid @-@ stride ) . However , Holtz ( 1998 ) concluded that tyrannosaurids and their close relatives were the fastest large theropods . Christiansen ( 1998 ) estimated that the leg bones of Tyrannosaurus were not significantly stronger than those of elephants , which are relatively limited in their top speed and never actually run ( there is no airborne phase ) , and hence proposed that the dinosaur 's maximum speed would have been about 11 metres per second ( 25 mph ) , which is about the speed of a human sprinter . Farlow and colleagues ( 1995 ) have argued that a 6 @-@ 8 ton Tyrannosaurus would have been critically or even fatally injured if it had fallen while moving quickly , since its torso would have slammed into the ground at a deceleration of 6 g ( six times the acceleration due to gravity , or about 60 meters / s ² ) and its tiny arms could not have reduced the impact . However , giraffes have been known to gallop at 50 km / h ( 31 mph ) , despite the risk that they might break a leg or worse , which can be fatal even in a " safe " environment such as a zoo . Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks ; this scenario has been studied for Allosaurus too . Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 to 40 kilometres per hour ( 11 to 25 mph ) , i.e. from walking or slow running to moderate @-@ speed running . A computer model study in 2007 estimated running speeds , based on data taken directly from fossils , and claimed that T. rex had a top running speed of 8 metres per second ( 18 mph ) . ( probably a juvenile individual ) . 
