I got major low gas millage lately
 

Before, I used to get 25+mpg, even when I used AC in ther summer, I would get 24+

However, lately, I've been getting low 19-22mpg. I haven't make any changes at all. And sometimes I can smell the gas vapor while driving. Can anyone tell me what may be the problem?

I just remember that I just put on a set of 18". But that wouldn't cause that big of a problem can it?

i bet they weigh a ton :oh:

check your timing

I was thinking if it's related to the spark plugs or anything.

spark plugs dont do much to gas milage
change them if taht makes u feel better. not that expensive

heavier rims, winter is colder therefore need for more fuel to mix with the denser air. check the air pressure in the tires lately?

I just did today, they're all good.

I guess what u're saying is prolly the only reason I can think of. But what worried me is that gas vapor that I smell quite often lately.

ive been getting a large gas vapor smell lately too and my gas mileage blows.. its getting to the point where im light headed every time im in the car thats how intense the smell is getting

Test your O2 and Coolant Temp. sensors.

and how does one accomplish this?