This is why I check the pressure in my spare tire every month, and also why some people who upsize tires or rims but not their spare will get into trouble. I Know a guy who replaced his stock 15 inch wheels with 18s and also did a major brake upgrade. He got a flat and guess what, his spare wouldn't fit over the larger brakes. Like everyone else says, if it is the same size, and the pressure is good you should be fine. As for replacing the flat I think it is a good idea to do at least two tires (both back if the flat is in the rear or vise versa).

JP Toronto

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Jason Priest
1986 420SEL