4 donut spare rims should fit motorcycle tires. in most cases motorcycle tires wil be 16" 18" or 20"
16s primarily being rears. and can be had in sizes up to 225 maybe more.
300/35-18 seems to be one of the largest bike tires.....
heres a good place looking for sizes.
Motorcycle Superstore Tire Selector
it would appear there are some very small sizes also. like 150/70-13s
on a very light vehicle these would be ideal as I dont think the sidewalls have much flex being the tirs tread prettymuch goes from rim edge to rim edge. it would also be a good aero tire. but I wonder how handling would be? but it shouldnt matter much as I dont see eco modders trying to speed or cut fast corners etc. as it would defeat the economy purpose