WHEEL SPACERS?
 

If they are not sandwiched between the hub and wheel like supermiata and BroFab spacers(possibly others of which I am unaware), and instead the wheels bolt to the spacers then they are not safe. At least in my opinion, not that I run any of that kind of thing on my car.

V8 Roadsters has spacers also.

Heres some discussion about those that happened a couple of weeks ago. They make two kinds the ones that are just a disc that uses the lugs on your hub, and ones that add a second set of lugs on top of your hub. I think with the small 5 or 10mm ones you shouldn't have any problem. Anything more than that like the giant 2 inch ones the "stance" crowd use really edge over into sketchy territory. I think the "safety" of them really depend on your use case. Would I run them on an endurance car? No. Would I run them on a car I took to car meets on saturday in the Wal-Mart parking lot? Maybe if they were my only option.

I used 25mm Amazon spacers with a second set of lugs for about a year with my stock daisies. It was a few years ago and I had just gotten the car, so it seemed like a brilliant idea to me. The spacers made the car a bit more responsive (darty) in the corners, and of course gave me some of that sweet flush fitment. I never blew up my hubs or sheared off any studs, but I only drove the car on public roads (albeit stupidly at times) and never took it to the track. That said, I probably put some excessive wear on my wheel bearings, and I'll just have to wait and see how long they last.

I moved away from spacers once I had enough money to buy wheels. My suggestion is to skip the spacers and save up for wider wheels.

Not on my miata, but 5mm seems fine on mr2