I am looking at getting some AU+ offset rims (do not exist in E-series offset) so I will need to use adaptors. The first thing I will do is take out the supplied studs and replace them with 1/2" Ford studs.
Originally when I was thinking about getting adaptors, I was concerned about the material quality of the adaptor itself, and was going to get my own made up from 4140 (overkill) but now I see there is very little need for that and 1045 will be fine (which is what most are made from I believe).

If the centre hub was to actually carry the load of the wheel, it would need to be a super hard press fit.

Lets look at some actual figures....

Car weight = 2000kg = 19620 N
Extreme case loading (all weight on one wheel) = 3924 N / stud
Shear capacity of M12 grade 8.8 bolt = 39,000 N
That's a safety factor of 8.9 with having all the weight of the car on one wheel.

Sure its a simplified look at it, and there would also be tension placed on top few studs (imagining the wheel trying to lean over during cornering), but there would also not be the full load of the vehicle on ONE wheel.

If you look into the friction of the joint between wheel and hub face you end up with a similar picture.
Coefficient of friction of aluminium to mild steel = 0.61
Ajax bolt guide Recommended tightening of a 12mm Grade 8.8 bolt = 77 Nm which converts to 31800 N tension.
Total tension at joint of ONE wheel = 159,000 N
Friction force of ONE wheel = 159000*0.61 = 96990 N
Car force (TOTAL) = 19620 N

So again if we put all the load on ONE wheel the safety factor is 4.9.


Now this is looking at these things separately.
If the vertical load is never enough to overcome the friction then the studs will NEVER take any load in shear.
If the vertical load does overcome the friction, then the studs would start to take the load. Not all of it though as the friction would still be assisting.


Now most wheel studs are what's called 'grade 8' which is basically the imperial version of the metric 'grade 10.9'
I didnt use grade 10.9 because I wanted to show the worst case situation, and th ebook I have doesnt show the shear strength of grade 4.6.

Ok, now go learn the more advanced engineering principals and come back and tell us what you just said is still true.
Add in dynamic loads (as well as the tension forces on the studs due to lateral loads during cornering) and some corrosion and fatigue factors. all your calculations are good for is that the car can carefully be balanced on one wheel without it falling off. Im not going to bother quoting any numbers here as to give a truly accurate representation of what is going on i would have to go through textbooks.

The vibration problems reported by people on cars with poorly fitting locating rings outlive the problem exactly, the wheel is flexing the studs (lateral G's will reduce the clamping force exerted by the studs) allowing vibrations this flexing is doing mechanical work on the studs, this mechanical work is probably within the elastic deformation range of steel ( so they will never plasticly deform) BUT it is conceivable that the stud will eventually crack through fatigue this crack will propagate until the yield point is reached (being high tensile there is probably a minimal region of plastic deformation)