a little help please on backspacing and offset

alright, right now i have enkei rims that are 18x9.5 with +15 offset wrapped in 285 65 18 firestone MT's. i used to rub my UCA's, but i installed spc light racing UCA's and that stopped the rubbing.

i just ordered some ultra 198U rims, and they are 18x9 with +12 offset.

i dont like the wider stance, i want it narrow and tall (like i have it now)

will this fit? (the ultra 198U's i ordered)?

everything i have read says that i need -12 offset.

everything ive read also says that the current setup i have right now (the 18x9.5 with +15 offset) should NOT fit, yet it does.

i just want to make sure that the rims i ordered will in fact fit. thanks guys!

 

P.S., i have around 2.5-2.7 inches of lift with my fox coilovers