i recently put 18's on my mazda 3i and i was thinking about lowering my car about an inch. but the other day i had 6 people in my car for about 5 minutes and i heard the wheel hit the wheel well or whatever its called, i dont know alot of car terminology but i know that that is not a good thing. my friends told me its because the stock springs are garbage and that if i get after market springs that are somewhat decent i could still lower it. just let me know if u have any info about this. thanks

Not an expert here, but 18's are pretty big already and if you still want to lower it new springs would help, but even with a stiffer sport suspension you are probably going to get some rubbin of the wheels in the well if you are going to be carrying 6 people.. you might want to consider 17's in this case, or just always have 6 people in the car so it always looks lowered anyway :D