I will be shopping for tires soon. What size is ideal for a 14x6 wheel.
In the Kumho Victoracers there are:

185/60/14
195/55/14
205/55/14

I am between the 195 and the 205. Will a 205/55 fit nicely onto a 6" wide wheel?

Thanks...

You can squeze a 205 on a 6 inch wheel but it's wide for that wheels size. I run 195 azenis on 6.5 wide wheels for street tire autocrosses. If you're running in street preppared though, you need to go shopping for wheels too. Wheel width is unrestricted in SP and 6 inches ain't gonna cut it.

I currently have 15x6 wheels that I use daily and for autocross. I have 205/50/15 Azenis mounted on them now. I think the tire matches perfectly to my wheels. Nice and square fit.

I thought maybe that a 205/55/14 on my stock 14x6 wheels would have the same aspect ratios as my 205/50/15 on my daily 15x6 wheels.

Same width and height...?

R compounds usually run wider than street tires of the same size. My 225 Hoosiers are 10 inches in section width as an example. Go to Kumho's website and look up the victoracer. They give specs there on the section width and recomended rim for each tire size. Kumho usually "Allows" you to run a given tire on a more narrow rim than Hoosier would recomend. You can get a 205 on the 6 inch wheel and you may be competitive locally with that arangement. In SP though, the fact that you can run almost any wheel and tire seriously handicaps you if you're running the same size tire that the Stock class runs.

What size wheel would you recommend to be competative nationally?

I'm running 14x8's with 225/50-14's. Bill Harvey's car has 15x9's with 225/45-15's. Miata's give you a bit more flexability as you can run some 13's (I have a set of 13x9 keizer's for a Miata and they clear the brakes on the later M1's - not sure about the M2's) Most of CSP seems to be on the 225's and if a 245 is made available again which MIGHT happen next year, then a 9 inch wheel would be about right. You can stuff a wide tire on a smaller rim but as you bend the sidewall in, you loose contact patch so at some point on a given wheel, going to a larger tire stops buying you anthing and may work against you.
I had Independent racing wheel make a set of 14x8's for my car (just under $300) and they work reasonably well but are a bit heavy at 16.5 lbs. Miata's are very sensitive to unsprung weight so you ought to look for a lighter wheel. that said, the 4x100 bolt circle is pretty common and I've seen more than a few very good ebay deals that made me wish I could run that PCD. If you run on some of the small local spots like palm bay mostly, then I'd look for some 13x8's and put 225's or 235's on them. I think the 235 was only available in the Ecsta V700 but maybe was available as a victoracer too. Tim Aro was running 13's (at least one of those days) on his MR2 at the National Tour and they obviously worked well there. As you go down to 13's you effectively lower your gearing which could work against you on higher speed courses. Kosei made a 15x8 K1 that wasn't too expensive and is fairly light but I heard that size was discontinued. I'd say on a Miata you really want to keep you're wheel/tire weight at or under 32lbs if at all possible.
Take a look on Miata.net or ask some of the competitive guys what they're running. At the very least, If you wanted to go with the 225/50-15 victo's, I'd look for some Kosei K1's in 15x7. They are fairly inexpensive and pretty light to boot. A bit narrow in my opinion for 225's but probably wide enough to be faster than 205's on 14x6's. Deffinitly talk to some Miata guys before you buy anything though. They may know of some good deals so you get more bang for the buck.

Thanks

If you want to be nationally competitive in CSP, you'd go with a 13x8" wheel.
Rob Falkner is running 225 50 14 Hoosier A3SO4's on 14x6 wheels on his ES Miata!
Some of the GS Civics are running 225s on a 5" wide wheel.

I thought the widest tire that could be optimal for a 6" wide wheel would be a 205.
225 seems that the wheel and tire might look like a dounut with bulging side walls...

Optimal maybe, but the SO4 Hoosier sidewalls are so stiff that they work just fine on a 6" wheel with a little less air pressure. Rob is an Evolution instructor and multi national champion, and hella fast in his Miata. He's gonna surprise more than a couple MR2 drivers.

Ummm, Rob Faulkner has NEVER won a Championship. He's fast enough to do so, but hasn't done it yet.

I think he can trophy in ES, but I don't think he'll be able to beat the likes of Cashmore.

Never said he will win ES, just that he'll surprise several people that have written off the Miata in ES.