I know what offset is. Where the hub is in relation to the wheel. Correct me if I'm wrong, please. But I don't know how the numbers work, like what does 42 mm mean? I did a search too. Thanks in advance.
the numbers are basically how far the the hub is to the front of the wheel from the center of the wheel...+'s go from the center to the front and -'s go from the center back...ie...a +49mm will have less of a lip versus a + 42mm...and a -4mm will have less of a lip versus a -10mm...hopefully this helps in some way.