The Overall Diameter of the 205 60 R15 is probably a little lower and it may also be a little wider. I believe it is within a safe range (maybe 0.3"), but I personally don't like mismatched tires on my car. If you are going to buy new tires soon, then I would ride them out until then.

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz