Using a spare with wide tires

[Performance nut]

Anyone know if there is a limit to using a donut with wide aftermarket wheels? Height wise, my new wheels and tires are really close (within 0.5" overall height). Width is way different. Stock was 235, my rear tires are 305.

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[69mach1-395]

Besides looking really funny, I don't think there is an issue for the few miles this should occur.