JARblue

Changing the width of the tire will not affect the speedometer (as far as I know - someone please correct me if I'm missing something). A change in the tire diameter would affect the speedometer. Traction control is not affected by your choice in tires.

I think the general consensus would be that RE-11 > S-04. As for your last two questions, they are difficult to answer without some fundamental understanding of what you're looking to get out of the car. My Z is a DD, so my approach to modding and maintenance is going to be different from a guy who tracks or does a lot of auto-x events. The difference between 275 and 285 is pretty minimal, but I like the look of the wider tire. In racing, the wider tire is not necessarily your best option.

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