I searched and am now more confused than before I searched...

Alright so I'm looking for some 18-20" rims for the RL...

I know that they are RARE and hard to find something that will fit the caliper space, however, what offsets are ideal for each size?

18 -
19 -
20 -

And so on. I know that the OEM are +55 on both the 17" stock and 18" aspec, so I think that it should be ok for any 18" to be at +55, but what about 19" and 20"?

 

In large part, this is dependent on the width of the wheel. Both the 17 and 18 Acura wheels are 8" width. The other factor appears to be clearance issues associated with the front 4 piston calipers. Consider that RonJon stuck with the stock 8" width, but purposely designed the wheel with a 45 mm offset to give it a little more width in the stance, and found out upon receipt of the prototype, that he needed to change the offset to 41 mm because of clearance issues.

But the largest factor is the width of the wheel.