Got our new '04 RX8, MT yesterday and so far am very impressed. I am going to spend the summer looking for a deal on winter wheels to get through the Michigan winter. Question is, would you guys recommend 17" with matching tires or stick wth the 18"? I did a similar swap on a Honda I had and when going to the smaller winter wheels, the alignment was off, when going back to the summer rims, all was fine. I have to believe the 17" would be better in the snow, but if not, why mess with it.

 

I went for a winter set in 17". Broader choice of tyres, cheaper alloys, probably better suited for snow too.
Keeping 18" maintains the original look though.

F

 

This thread https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/winter-wheel-tire-pics-installed-28442/ should have enough info.

But like ^ He said 17" is the way to go.

 

The wheel diameter actually doesn't matter at all - the tire diameter does, and the tire width is the most important factor to consider when choosing winter tires. (Re your Honda - changing wheels/tires can not affect alignment, but your winter wheel's offset, if wrong, could change the contact patch relative to the kingpin angle, and screw up steering and braking feel).

Anyway, back to RX-8s - for winter use, narrower is better. There are no 215 width 18" diameter winter tires available (at least in anything close to the correct diameter), so just from that factor alone, a 215/55-17 is the "best" winter tire size since it's one size narrower than the stock 18" tire, but almost the same diameter as the stock 18" tire. Factor in that 17" wheels, and 17" tires, are cheaper than 18" ones, and there's another plus to running 17" winter tires/wheels.

Regards,
Gordon