S13 or S14?
If it's a S13 - Forget about it. Unless your car is the most savage 240sx in the Western Hemisphere you will not be able to pull off 19s. It will look utterly fucking ridiculous.
If it's a S14 - Depends, but more than likely you should still forget about it. With the right stance and body kit (among other things) you could probably pull off 19s in the rear and 18s up front. Your car will have to be pretty damn crazy to make it work though.
You can make any wheel fit with relatively little effort, but making it look good will take A LOT of hard work and money.
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