I suspect that the drawing by Mitsubishi which shows the offset as being from the centerline to the outside edge of the wheel's center is incorrect - but since these are "dually" rims I suppose when used on rear, the mounting surface is on that side... hummmmm....
I would do the calculations using the backspacing - so much easier to measure than the imaginary "ET" offset spacing.
don't forget the thickness of the centre of the rim. I think its called the thickness of the disc in Mitsi drawings. Put another way, the mounting face of the rim is different if rim is reversed for front/rear. Or, from the above, the offset is different for the same rim depending on which face is mounted.
That was my guess and how I based my cals. Funny thing is though, the part of the rim that touches the actual bolting surface is in the same orientation front and rear. i.e the front rim has the tire offset towards the truck and the inner rear dually is the same orientation, so the mounting surface front and rear is the 'inside' of the rim, not the outside as their offset dimension would lead you to believe.
I haven't had to get into the detail but I would define offset (for the purpose of achieving equal front and rear track with the same rims) as from the centre line of the rim to the centre line of the centre (disc). Makes the calculation for same track front and rear a little easier. Alternatively define two different offsets, one for when wheel is on the front, the other for when its on the rear.
I have to use two different offsets. Since the wheels he is looking at aren't reversible, this is a requirement.
The other essential distance is the distance between mounting faces (bolt faces) for front and rear axles. At first glance, there's just enough info to calculate in the diagrams. Then I'd measure it.
I've always considered equal track front/rear as being distance between centre line of tyres is equal. I haven't a clue if that is "industry standard" definition.
Yes, this is how I determined that too. Mitsubishi gives the track tot he centreline, so I did the same.
Alright, this is how I determined the numbers I got. I probably didn't have to draw it, but it seemed easier and would allow me to change the location of the wheels easier if we wanted.
Front:
Used the FT number (1650mm). Then I took the Offset of 135mm from CL to face of rim and subtracted the 9mm that it mentions on the tire portion. Did this on both sides and got a mounting face to mounting face of 1902mm.
Rear:
Same concept, used the RT (1542mm) and used the same 135-9 to get the mounting surface to mounting surface of 1542mm
Then, I used those two numbers as my basepoint. I think the thing I am unsure about whether the mounting surface of mounting surface is correct.
I then took the difference of those two and lined up the center of the front and rear tire. This gave me a track of 1722mm front and rear. I can then calculate the offset based on this number. I also split the offset between the two rims or I could reduce the offset on one and add it to the other while keeping the same track.
