Here is what good-win-racing.com has to say about it:
"Weight. The Mazda Miata is incredibly sensitive to what is called unsprung weight (which can best be understood as what hangs off the Miata suspension rather than what sits on it). I was surprised when I bought my first Miata in the early 90s when I ended up not enjoying the very first set of very nice wheels I picked for that Miata because the ride quality became poor. Most Miata owners can feel a deterioration of ride quality from a gain of as little as 2 to 3 pounds per corner in unsprung weight. We therefore strongly recommend that you use only light weight wheels for your Miata like those we sell here."
I think I read somewhere that my stock 16" wheels are about 15.5 pounds, whereas one wheel Good-Win-Racing seems to like, the Konig Helium, weighs only 11.4 pounds (for 15"). Now, that's a big difference, and I wouldn't think the slightly taller tires I'd be running on the smaller rims would really change that.
So my question is, is Good-Win-Racing right? Will 4 pounds per wheel make a big difference in ride quality (among other things)? When the roads are good, I don't have any complaints with what I have, but on the occasional bad patch of interstate or the like, well, it's not so good. I've just gritted my teeth and sorta assumed that was one of the tradeoffs of a sporty car with an 89-inch wheelbase.
The other question is if there's a downside to light wheels (other than maybe cost). Otherwise why would stock Miata wheels often be in the 15-16 pound range?
(On that site you can get a set of the Heliums with Toyo T1Rs for about $750. Not sure if I'd run right out and replace what I have now since my tires are basically new, but I would at least make a note of it.)
Eric