This is one of the most asked questions on this forum.
I have 225/50R16 BF Goodrich g-Force TA KDWS (not KDW) on my 98 SVT EO. They have about 15K on them. Before that I had 225/50R16 Continental 4000H tires for 60,000 miles.
The BFG's are slightly wider than the Conti's but in either case the fit is tight but adequate. The fronts fit fine and is not close at all. The rears are close to the struts and the trailing arms but there has never been any indication of rubbing.
According to the tire calculator that can be found on the Miata group site, the 225/50R16 is exactly the same diameter as the 205/55R16 that my car came with. The 225 is about 3/4 of an inch wider. The 225/50R16 is both slightly larger in diameter and slightly wider than the 215/50R16 that came with the 99 SVT.
There was an issue on some 99 SVT's with the rear tires rubbing on the fender liners with the stock tires and there is a TSB with part numbers for a revised tire liner with a little more room. Most people that have posted on this forum with the larger tires have not had this problem though.
If you ask Luke at Tire Rack about this size he will suggest that you not use it. I believe that he is being cautious, as he should be. When I ordered my tires from him he called and confirmed that I wanted that size. When he shipped them he had noted on the invoice that size fitment was customer responsibility.
So to make a long story short, may are using that size with no problems but you may never know for sure until you mount up a set and try them out.
My car runs, drives, and rides great with these tires. I'll probably never have anything else.
