I have 16in wheels with tires that are 33.1 inches tall, but i don't want to spend the money on another rim and want to use my factory rim with same tire. problem is i have an 18in wheel and the tires for 18's run 32.4in and 33.4in. So will i be ok if i run one of these tire if need on the trail for a day or two. would this cause issues since size would be very close? Which size little bigger or smaller?

 

it depends on what the actual measurement of the tire is, mounted and having weight on it and at which psi. If you really want a full size spare, and the same size wheel you could just get a cragar soft 8 or pro comp steelie wheel to throw on the back. Thos wheels are only 40 bucks or so. That way, you can get the same tires that are on the ground, and they'll be the same size.

plus, tires for 18" wheels are expensive.

 

So would buying a Rim and tire. Im going with the same tire, if that makes a difference.

 

All you really need, is the spare to be within spec of the rest of your tires so you can get home without having to grind the ABS and fight ESP the whole way. If you go with an 18" wheel tire, and it's a half inch larger, it will need less psi to match the height of the others.
Hardest part is getting through the electronics.