Offset and Backspacing (error?)

[Juan]

Hi everybody,

I was searching the forums and I found the wheel offset calculator site. I linked, but I have some questions about it:

A 7 inches wide wheels is actually 8 inches wide = 203.2 mm

So if I have an ET52, backspacing would be

Rim width / 2 + ET
or
(Rim width + 1) / 2 + ET ????

what´s the correct answer? 140.9 mm or 153.6 mm????

[zen]

official rim measurements are bead to bead, not the true width of the rim.

offset is the measurement of the distance of the hub mounting surface from the center point of the rim width.

backspacing is the measurement of the hub mounting surface to the inboard side of the rim.

they are not the same measurement.

to keep things simple, if your rim is 200mm and offset is 40, the mounting surface is 40mm to the outboard side of center (the 100mm mark). the backspacing would be 140mm.