Recently, you confirmed that a winter tyre can be used as a 'spare' in the summer; or a summer tyre can be used in the winter; provided it is treated in the same way as a space-saver, and kept below 50mph. What if the two sets of tyres are on different wheels, eg 16-inch winter rims, and 17-inch summer ones?

Same overall diameter tyre, of course, to compensate for the different rim sizes. I can see no reason why your answer shouldn't be the same, but would appreciate your guidance.