I want to respond to this…
To add to the last paragraph about spacers. Adding spacers, adds unsprung weight which results in less efficient acceleration, heavier and less responsive handling, worse dampening and greater discomfort and harshness in ride quality. Spacers end up being a quick fix and a long-term waste of money, I’ve never seen as much of a car community abusing spacers as much as s-chassis owners.
Also try these net calcs although it is just theoretical, in practice the tire width and profile affect the fitments too.
http://www.1010tires.com/WheelOffsetCalculator.asp
http://www.miata.net/garage/tirecalc.html
17" wider tire sizes are readily available up to 255, up above that you get availability issues (eg; me considering 275/40/17 tires).
To run a 18" rim you would have to run a 35 profile or even (depending on width of tire) a 30 profile tire… to stay within standard tire diameter sizes, and it does look descent it’s been done properly on Japanese tuned cars, but it is not recommended, japan has glass smooth roads, compared to the garbage we have in Canada. Also what comes to my mind when 18" rims are mentioned for an s13 or even s14 is chrome bling bling rims with ugly spinners or something like that… and of course very crappy high offsets… in other words, think about that.
Go with a 5 lug conversion as well, it’ll benefit you long term. I currently run skyline gts rims, but I will probably switch to some lightweight 17x9 +10 rims in the near coming future to run a 255/40/17 setup. Another question to ask yourself is whether to run a staggered or non-staggered setup. Depending on your goals and intentions think before you make a decision but don’t waste money on spacers.
My father has a 225/50/16 tire fitted to his Taurus 6" rims, and well it runs, and grips well, but it looks like a crazy setup.
People emphasize too much about stretching tires especially da dorifto crowd. All stretching does is preload the tire, so that the sidewall becomes very very stiff as we do not run race tires. so although someone says it’s impossible, it doesn’t mean it’s not.
Check these out:
17X8 275/40/17
That’s almost what my father’s taurus now looks like lol. So you can tell how bulged the tires are.
Being ‘flush’ or having a stretched tire, or staggered setup that people in the s chassis community encourage, may not actually be the best setup for the car’s actual handling. It may contribute to ‘the look’, but it may not be such a good idea. Rethink your ways