A mule car is a current vehicle that has been heavily modified with parts from a new design for testing and development purposes. You make as many changes to a mule as you need to, to make it representative for the tests you want. The term 'Mule' has only been applied to vehicles where the purpose of the body shell is to act as a vehicle to carry engine/transmission/suspension development actions. Hence the Mule just carries the parts. Most mules are for ride and handling, road loads, and powertrain/driveline work. (Info from: https://www.eng-tips.com/viewthread.cfm?qid=199247)
I just found this one today, but I have no idea where the term originated.
I just found this one today, but I have no idea where the term originated.