A Perth police officer who was "shown up" in a foot chase as being "too old, too unfit and too overweight" has been convicted of dangerous driving after ramming the teenage suspect with his police car.

Richard Moore, 56, was found guilty of dangerous driving on Monday following a two-day trial in Perth Magistrates Court.

The senior sergeant and his colleague, Heather Osborne, were responding to a call about suspicious activity in Thornlie on May 6, 2018, after a man was said to be scoping houses by knocking on doors and asking for cigarettes.

The pair spotted William Farmer, 18, who ran off. They took chase, with Moore falling over twice before they caught up with the suspect and attempted to arrest him.