m trying to make some discs but when i put them on the car there are black corners on the pic and they show up under the wheel..

how do i get rid?

maybe you should take a screenshot, that we can see your problem ... but i think, you haven't an alpha channel in the picture

here is a pic, its not very clear tho but u can see it

Off the top of my head, that's a transparency issue. I've had this problem
once myself. Either it's the worng color or the channel is empty (no mask).
Someone with more experience should come along shortly explaining the
details better, i hope.

Check here: http://www.lfsforum.net/showthread.php?t=4119