In the US you are allowed to modify your vehicle any way you want. The federal government puts limits on what manufacturers can do with vehicles (eg safety rules) and they have a federal rule that alll corporations must adhere to known as the "do not modify rule". But your own vehicle can be modded by yourself anyway you want.
States may have safety rules you must abide to, such as braking etc. Many do not but thats where the enforcement of rules sit. Oregon is famous for having almost no rules as to what modifications are legal.
This is my buddy's volvo. Converted to a SUT (mini-pickup) with homemade roof rack. Needed AC in the desert so got a window ac at the local walmart and welded it up on a shelf in the back window. A 110v generator runs the AC. Its colder than a butchers pantry in that car... Its pretty sketchy, held together with flashing metal for roofers and tape. That AC can fly off the car if it hits something make make some serious damage. Not to mention the homemade roof rack riveted to the sheetmetal roof. Sketchy...
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And this is my other friends lifted limousine. It required no registration or inspection in oregon. He got pulled over by highway patrol and they told him that his lights was too high and he was not having mud flaps. He fabbed the mudflaps out of sheet rubber and he made brackets for the headlights to drop down 5 feet from the housing. He still gets stopped by the police but they can't find anything to nail him on. In some ways i love america and its freedoms (i'm born in europe) but in other ways i also sometimes fear some of the things you can legally get away with here...
Overall i love these freedoms - try to build a street legal 10-15ft tall limousine with offroad armor and tires and drive that on the highway in europe....
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