BBS rim width measurement

[sbmackie]

Just picked up a very nice set of BBS RG's (one piece). Sold to me as 7.5's and 8.5' x 16's. Measurement on inside of rim (let's call it "tire bead width" is roughly 7.25-7.5, depending on how I hold the tape. The others are 8.25-8.5. The outside measurements (outside of rim to outside of rim,) 8 and 9, respectively

With that in mind, how do tire manufacturer's determine the approved rim width? Inside (bead width) or outside (aint' my rims cool width)?

Google search leads me to believe inside diameter.

Follow on question, can I mount 205's on the front 7.5's without overstretching them? I'd like to use 225's in the back as there are more street worthy tires in those sizes then in the 225/245 combo.

FYI, the part number stamped into the wheels is 0043005 on the 7's and 0343006 on the 8's if that helps.

Thanks
Scott