Falcon wheel offset help

shazza541, Sep 25, 6:18am
just wondering what size spacers you need to run AU falcon wheels on pre AU falcon! xe/xf etc. The XF rims are 15x6 with +6 offset and the AU are 17x7.5 +35 offset

rkauto, Sep 25, 6:57am
you get the correct ones to start with

franc123, Sep 25, 8:41am
You've answered your own question, whats 35 minus 6!

fordcrzy, Sep 25, 9:53am
answer= ILLEGAL

crzyhrse, Sep 25, 9:54am
Not quite. Need to take into account the increased width too.
7½"-6" = 1½", or ¾" either side of centreline. That places the inside of the 7½" rim ¾" further in to begin with. Factoring in the 35mm offset compared to a 6mm offset, to make the wider rim inside edge in line with the where the narrower rim would be, you'd need a 48mm spacer (¾" x 25.4mm/inch + (35mm - 6mm)).

But at the end of the day that isn't the whole equation anyway.

bill-robinson, Sep 25, 5:57pm
The offset is the same regardless of rim width.
if the inside rim hits it is because of rim width not offset

crzyhrse, Sep 25, 9:13pm
No. The offset is from the centre of the rim to the mounting face. When the rim is wider but with the same offset, the distance from the mounting face to the inside of the rim increases, thus the wheel protrudes both further in and further out by half the difference in width.

bill-robinson, Sep 25, 10:54pm
Do you want to think about what you said. The first sentence is correct.

crzyhrse, Sep 25, 11:12pm
I don't need to think about what I said. It's all correct.

bellky, Sep 25, 11:19pm
this is correct - sorry crazyhorse. the offset is the direction and distance the mounting face is from the centre of the wheel width

bellky, Sep 25, 11:20pm
obviously +35 and +6 are different offsets however

crzyhrse, Sep 25, 11:24pm
Another one who can't read.

crzyhrse, Sep 25, 11:27pm
To work out if a rim will fit you need to know the width and the offset as I demonstrated above.

In this scenario both the offest and rim width vary between the wheels so just knowing the rim width alone will not tell you if there is a clash.

bellky, Sep 25, 11:30pm
OP - you need to find the maximum backspace of wheel (and tyre) you can fit before hitting any suspension components with the wheel/tyre. you also need to know the distance from mounting hub face to the outer guard so the wheel/tyre doesn't stick out - once you know these two measurements (and the maximum wheel/tyre width you can fit) then you can use the prospective wheel/tyre width and offset measurements to work out if they will fit without touching suspension or body work and whether or not you will need spacers.

spacers are legal with cert

bellky, Sep 25, 11:35pm
OP - you will need spacers to fit [17x7.5 +35 offset]. you need to find your backspace on the car, and the backspace of these wheels and the difference is your spacer requirement.

bellky, Sep 25, 11:37pm
OP - 7.5s will fit no problem though, i think you can get 8.5s on front of xf, and something like 10s or 11s on the back.

shazza541, Sep 26, 12:33am
thanks heaps for your help. yes i know getting the right offset wheels would be easiest thing to do but that is not going to happen. For now I will try track down some 20mm spacers to try and fit on. If they clear everything fine I will get them certified

bellky, Sep 26, 3:31am
^^ this is a good idea - sometimes you just need to try and see because the maths involved is too difficult! haha

shazza541, Sep 26, 6:24am
I jacked the front of my ute up and the max backspace I can have is 120mm. So if my wheels are 7.5" (190.5mm) wide with offset of +15 that gives a backspace of 110.25mm and foward spacing of 80.25mm. Starting to look promising

bellky, Nov 21, 3:05pm
^^ yes sounds good - better to work it out a bit before purchasing expensive spacers i must say.