Please dont get angry, that is not what I wanted at all....
I acknowlegde that you are smarter than most, and what you are saying is absolutely correct in this situation, HOWEVER, some wheels need a bit more information..
Once again, I will say that the offset CAN affect the caliper clearance - but in a way you may not have seen on the wheel and brake combinations you've worked with.
Please read on.
Not all alloys have a perfectly flat mounting face like the one you have pictured. A lot of alloy wheels made today come with a step on the mounting face that determines the offset of the rim. By making this step THICKER, the wheel's offest goes more into the "+" without changing any other part of the wheel's design. They can keep the same 20mm dish on a particular rim right across the offset range simply by modifying the mounting flange step thickness and the depth of the stud hole taper.
I have taken the liberty of modifying your diagram to show you
*note - this may not apply to your wheel Mokesta, but it does apply to other makes that are on the market..
Okay.... here you can see I have included the mounting flange step (as found on some wheels), coloured in blue.
By increasing or reducing the thicness of this BLUE section, the clearance marked in RED changes accordingly. Also, by increasing the BLUE thickness, the wheel manufacturers can change the offset of an alloy wheel without changing the face profile (dish) or visual appearance, because the mounting surface is infact moved closer to the rear of the rim.
If you were to order a new alloy wheel package from TyrePower or wherever, and the brochure says that the wheel comes in +20, +32 and +40mm offsets, you will find that alot of manufacturers simply machine down (or change the casting) of the thickness of this step on the rim. By doing this, every size rim will have the same profile and dish of the one in the brochure. This may simply be a way of cutting costs, who knows....
Lenso Wheels are guilty of doing this. I am 110% sure. I can think of at least 10 wheels in their range that are available in different offsets by having a different step thickness - and they all have the exact same dish size.
Now, depending on the make of car and profile of the caliper in relation to the mounting flange, this step makes a GREAT deal of difference. If you are using a larger caliper (eg: 4 pot or 6 pot) or a custom brake setup, the face of the caliper can be much closer to the face of the mounting flange face on the brake assembly, and would possibly foul the RED distance in the picture OR between the caliper and the back of the spokes.
Some calipers I have seen on other cars stick out further than the mounting flange, so without the step on the wheel, it simply wouldnt fit on without fouling the wheel spoke on the caliper.
The only thing I can think of is that you have never seen this design feature on a wheel before.... maybe because it has never applied to your situation.
I'm not saying that you are wrong, I am simply pointing out that there are other factors that need to be considered with SOME of the wheels and brakes that people are using... but obviously not with the alloys you have drawn.
Sorry if I am getting you angry, that wasnt my objective at all.
PS... let's please not assume that ALL Qualified Engineers are gods. Some of them are old dogs that cant and wont learn new tricks. Trust me - I work with some that are completey one-track-minded and believe everything they know is "the way". I may not have a Laminated Certificate on my wall that proves my intelligence, but I might know a thing or 2 that they dont... and maybe even 3
