Its on the inside of the wheel, stamped into the alloy, also sometimes called off-set, its how far you wheel sits from your hub, if you get the wrong ET you wheel will rub on your wheel arch, not good.
You dont need to change anything to put 19inch alloys on your car, just get the correct size of wheel.
eg. 19inch, 8.5J, ET48, should fit your car ok. 19inch, 9.5J, ET40 will not if your car.
sound good, will it look like its on stilts if i dont lower it though? also on the sticky wheel guide it says offset is 45 not 48 :o im confused now ?
thanks for the help