As a supplement to my previous post, here’s a short post about wheel offsets.
So without further ado, let’s beat that dead horse, shall we?
If you look at a wheel along its barrel (width wise), zero (0) offset would be the imaginary line that is dead center between barrel end to end. The imaginary line is determined by where the backpad of the wheel sits. Keep in mind that this tutorial is based on MULTIPIECE WHEELS (which is what my previous how to determine lip post was referring to). Cast wheels follow the same idea, but the drawings I made are for multipiece wheels (since it shows lip size changing). If the backpad moves towards the outside of the wheel, then the offsets increase in positive numbers (in increments of mm). If the backpad moves towards the inside of the wheel, the the offsets increase in negative numbers (in increments of mm).
Rule of thumb: the lower the offset, the further the wheel moved OUTWARD of the fender, and vice versa. As you can see, the orange line demonstrates the fender position, and the blue line demonstrates the hub/rotor where the wheel mounts to. For general purposes, let’s say this wheel is a 18×9.5+0 (images are not drawn to scale). As you can see, the outer position is “flush” (even) with the outer fender imaginary line (shown in orange). Also take note of the size of the outer lip of the wheel. Let see what happens if we raise the offset of the wheel…
So instead of a 18×9.5+0, let’s try to run a 18×9.5+22 and see what happens. As you can see, if you change the offset of a wheel from a +0 to a +22, the overall position of the wheel is going to move INWARD 22mm. As you can see by the area shown in green, that is the 22mm that the wheel backpad moved between the two sizes. Since the wheels shown are multipiece, the face of the wheel moves inside the barrel to change offsets, rather than adding more material to the wheel backpad. In addition, notice that the lip size decreased when the offset increase. Generally speaking, one can assume that the lip size decreases when the offset increases, but sometimes it might not be the case (depending on face design, but that’s gonna get confusing).
So what have we learned? For those who don’t like reading, here’s the takeaway:
- Lowering the offset: the more it moves outward from the fender (”more flush”)
- Raising the offset: the more it moves inward inside the fender (”more sunk”)