18's

[chico]

looking to put 18's on 04 elantra sedan. any problems with going this big.i.e mess with gear ratio.

[BlackTibby00]

I hope that the roads where you live are fairly smooth. I say this because you ae more likely to bend a rim with 18's, than with a smaller diameter. But 18's would LOOK tight!
Also depending on a performance point of view, it will be less performance because of the added wheel mass the car has to turn.