The ratchet strap is after you get them on the rim. To get them on the rim, I use my Snap-On pry bars and wrap them with a few layers of electrical tape. You may have to re-wrap the bar after each rim but if you are careful you won't scratch the rim. I do it on powder coated rims and unless I slip, rarely scratch the powder.
Spray lots of soapy water on the bead of the tire. You have to put a knee into one side as you are pulling them on the rim with the pry bar to keep it from slipping. Once on if the tire won't take air, then you wrap the ratchet strap around the outside diameter of the tire and ratchet it down to push the bead out to the rim. Once the tire starts to take air release the strap.