Not. Method of purchase (cash or credit) is immaterial for depreciation purposes or figuring average cost per mile over a length of time for a car or bike. Presumably your bike still has some value when you rolled it out of the store. It will also have some value at the end of the evaluation/test period which should be factored in when computing cost/mile. Your "mistake" is in trying to compute cost/mile at an early point of your "test." Counting total purchase price over such a short distance skews the cost/mi far in excess of what will be seen in time after a normal ownership period.