You don’t get a speeding ticket in Arizona because you are going faster that the “Posted Limit” Arizona Revised Statute 28-701 does not even have the words “Posted Limit” anywhere in the text.

You get a Speeding Ticket because of line A in 28-701A.

A. A person shall not drive a vehicle on a highway at a speed greater than is reasonable and prudent under the circumstances, conditions and actual and potential hazards then existing. A person shall control the speed of a vehicle as necessary to avoid colliding with any object, person, vehicle or other conveyance on, entering or adjacent to the highway in compliance with legal requirements and the duty of all persons to exercise reasonable care for the protection of others.

Google “Arizona Revised Statutes 28-701A” and read it for yourself.