I'm not sure what you mean by " 3 wrappers and Oregon 4." Are you referring to the chains themselves ??? If so, yes here in Washington State the DOT requires 4 drive tires to be chained, along with 1 trailer tire on each side. With most tractors having tandem drive axles, you chain the outer tire on each axle. Some drivers carry stepped blocks to run the inside tires up onto, making the job a bit easier. Tractors with only a single drive axle are another story, an ugly story. You have to either hang 4 singles, or 2 of the Three-Railers you mentioned, which as the name implies have 3 chain " rails " around the tire circumference - inner, center, and outer. While three-railers are somewhat easier than 4 singles, they are much heavier. No matter which way you go, the inner tire is a pain to chain up when you're driving a single drive - axle tractor.