For a project, I welded up a forged aluminum Thunderbird (4 bolt, 18") high-pressure mini-spare and redrilled the wheel to 5 bolt. With a dropped battery and some rearranging, it fit up front in my car while inflated. Never heard from the guy who bought it so maybe it fit OK in his car, or maybe not. I posted this a few years ago. Somewhere in the PI Archives is a follow-on post by Mangusta-Steve Liebenow on other such high pressure spares that will fit without changing bolt patterns.
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