Looking at getting some 15" BBS RA's soon enough, but I'm confused by some of the terms. ET35 is the offset right?? But what is the offset?? Can it be higher/lower?? What difference will this make?? Also, 6J, is that the width of the alloy?? 'cause I'v seen some that are 9J, I'm assuming 6J is close to 195 width??