One rider no passengers
4 dollars per gallon for fuel:
Tires is a major cost. 350 bucks a year. Chain kit every other year = 125 bucks a year. oil change = have to do for cage too. So everything else constant, we are looking at least 4 bills over and above what it cost to operate a cage. Cages need tires too. Every 5 years so add 100 bucks a year for cage tires.
20 mpg Cage fuel = 10,000 miles or 500 Gallons = $2,000 just for fuel + $100 for tires = $2,100 yearly cost
40 mpg Sickle fuel = 10,000 miles or 250 gallons = $1,000 for fuel plus $475 for tires and chain kit = $1,475 say 1500 for a savings of roughly 6 bills a year.
More detailed analysis would yield tighter results, but the point is the savings of operating a motorsickle are eroded by higher maintenance cost of operating a motorsickle.
