Based on the findings with the mesh quality feature, I have done a quick test to see how changes in CAD geometry and Mesh settings affect the total Nonorthogonal cell count.
PLEASE GIVE ME ADVICE AND GUIDANCE HERE. I WOULD LIKE TO UNDERSTAND THIS CONNECTION BETTER SO THAT I CAN GET BETTER MESHES QUICKER.
@DaleKramer @Ricardopg
Below is the full list of settings i used for the half car sim. I will track changes of the settings and also add pics of the solutions field results for each test.
Project LINK : HERE
Baseline test run from RH.31.15_Y.0.003_R.0_P.0_SA.0_S.16.5
Finished  11.1M cells, 13.1M nodes
Mesh  Half car and Wheel test 6 settings  Wheel test 6.1 settings  

Bounding box resolution  X  28  
Y  7  
Z  7  
Castellated Mesh Controls  Max local cells  4e+7  
Max global cells  1e+8  
Min Cell refinement  5  
Max load unbalance  0.2  
Cells between levels  1  2  
Resolve feature angle  30  
Snap Controls  Mesh to geometry conformation  7  10 
Tolerance  2  
Solver Iterations  300  
Relax iterations  8  
Max mex confirmation iteration  10  
Implicit feature snap  ON  
Explicit feature snap  OFF  
Detect features between multiple surfaces  ON  
Layer adding Controls  Layer size  OFF  
Max cancelled layers near sharp features  0  
Feature angle  180  
Slip feature angle  75  
Relax iterations  8  
Surface normals max smoothing iterations  2  
Internal mesh max smoothing iterations  5  
Max face thickness ratio  0.5  
Max thickness to medial ratio  0.3  
Min median axis angle  90  
Buffer cells between refinement levels  0  
Layer addition max iterations  50  
Max iterations with strict quality controls  20  
Mesh quality controls  Max non orthogonality  75 deg  65 
Max boundary skewness  20  
Max internal skewness  4  
Max concaveness  80  
Min volume  1e+30  1e+13  
Min tet quality  1e+30  
Min face area  1  
Min face twist  0.01  
Min determinat  0.001  
Min face weight  0.02  
Min volume ratio  0.01  
Min triangle twist  1  
Error distribution iterations  4  
Error reduction  0.75  
Relaxed max non orthogonality  75 deg  70  
Merge tolerance  1e6  
Results  Total Illegal faces  30  
Lower is better  Volume Ratio  127.3  
Should be Less than 150  Max Aspect Ratio  ?  
nonorthogonality > 75 degrees  16  
faces with concavity > 80 degrees  0  
faces with skewness > 4 (internal) or 20 (boundary)  3  
faces with interpolation weights (0.1) < 0.02  1  
faces with volume ratio of neighbour cells < 0.01  1  
faces with face twist < 0.01  9  
faces on cells with determinant < 0.001  0  
Time to Mesh  4026s 
Based off this information it seems that i need to reduce the Nonorthogonality to below 70°
Research has also alerted me to best practices for a healthy mesh as said here
 high aspect ratio cells usually appear in very fine boundary layers. It is not fatal for the solver stability, but can significantly decrease convergence speed.
 nonorthogonality (nO) is a very important parameter, we can define three ranges of its values:
 nO < 70  safe values
 70 < nO < 90  require special treatment of , e.g., nonOrthoCorrectors in fvSolution or numerical schemes in fvSchemes
 nO > 9O  bad mesh, which can not be used for simulation
 skewness  higher values may impair quality (accuracy) of the results, anyway any reasonably high value (<20) of skewness parameter can be used for simulation
TESTS
Wheel test 6

Mesh settings from Half car sim

Only level 4 active tunnel
Checking faces in error :
nonorthogonality > 75 degrees : 5
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 1
faces with face twist < 0.01 : 1
faces on cells with determinant < 0.001 : 0
VolumeRatio
min: 1.0000000000444333
max: 111.13924675573229
While there are only 5 nonorthogonal cells in this run, the Max Nonortho was set to 75° which falls in the “notsogood” zone of cells. The plan is to use the mesh quality feature to see where cells have Nonortho over the 70° value, and concentrate in fixing these areas.
It seems that the Bounding box layer addition (BL on floor) is terminating when the cells become coarse towards the bounding box cell sizes. These cells here are the very ends of the Boundary layer connecting to the floor. I do not know how to fix this. I am not sure why the BBLA is deleting layers here.
NOTE test mesh 6.1 and 6.2 are both used with the Wheel test 6.1 geometry similar setup is also done in test 7 & 8
Wheel test 6.1
New mesh settings used
 Cells between levels  2
 Max nonorthogonality  65
 Level 5 active tunnel used to increase cell fineness.
Checking faces in error :
nonorthogonality > 65 degrees : 2050
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 41
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.01 : 1
faces on cells with determinant < 0.001 : 3
volumeRatio
min: 1.0000000000168079
max: 258.62928332572926
The large increase in Nonortho cells is due to changing the MAX nonortho value to 65.
The increased level region refinement seems to have moved the Bounding box layer addition termination area to make this shape. It seems cell size does help but i think the layer adding settings could be the culprit.
Cells seem to be bad on the wheels inner hub and where the wheel meets the tire. CAD geometry changes might help this.
Wheel test 6.2
 Tolerance increased to 3
Checking faces in error :
nonorthogonality > 65 degrees : 2051
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 41
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.01 : 2
faces on cells with determinant < 0.001 : 3
The only change to this test run was increasing the tolerance to 3. I was hoping that the extra allowable snapping length would make the cells conform better to the geometry. This turned out to do very little. Below also shows the dark blue cells with a Non.ortho of 65, which are still acceptable.
Wheel test 7  Geometry change  hub simplification
 Tolerance back to 2
 Median axis angle 80
 Max Non orthogonality 70
 Relaxed 75
 Bounding box layer addition min thickness reduced to 1e6
Checking faces in error :
nonorthogonality > 70 degrees : 423
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 2
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 41
faces with volume ratio of neighbour cells < 0.01 : 2
faces with face twist < 0.01 : 2
faces on cells with determinant < 0.001 : 0
volumeRatio
min: 1.0000000000069633
max: 170.08380841806402
Wheel test 7 had some minor changes to the CAD geometry. By cleaning up the inner hub of the wheel, we can see the difference in Nonortho faces in this area with the following comparison
Wheel test 6 geometry  more complex hub (red) with spoke intersection (blue)
Wheel test 7 with simplified hub geometry
Nonortho cells show concentration at the spoke to wheel interface but not at hub
Looking at the actual mesh, it can be seen that the small step where the spokes meet the wheel is causing the problems (1). This is a geometry that should be changed to a simpler form in order to get a better mesh. However the hub mesh is very clean even and is the better meshing option even though the wheel now does not follow the real world geometry. (2)
Wheel test 7.1
 Explicit feature snap
Checking faces in error :
nonorthogonality > 70 degrees : 381 423
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 1 2
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 41
faces with volume ratio of neighbour cells < 0.01 : 0 2
faces with face twist < 0.01 : 0 2
faces on cells with determinant < 0.001 : 0
volumeRatio
min: 1.0000000000069633
max: 171.54233283960056
The only change for mesh 7.1 was the use of Explicit snapping as opposed to implicit. Just this one change reduced the Nonortho cells from 423 in Test 7 to 381. Other meshing improvements also occurred:
 Faces with concavity were reduced by 1
 Volume ratio of neighbor cells reduced to 0
 Faces with twist reduced to 0
Test 7.1
Wheel test 8  geometry change  spokes to wheel intersection
 Returned to Implicit feature snap
 Retuned medial axis angle to 90°
Checking faces in error :
nonorthogonality > 70 degrees : 384
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 1
faces with face twist < 0.01 : 1
faces on cells with determinant < 0.001 : 0
VolumeRatio
min: 1.0000000000021594
max: 107.21199797538466
The meshing log data shows slightly more Nonortho cells however Interpolation weights are not at 0. The Volume ratio has also dropped from 171 to 107.
In wheel test 8 I fixed the step at the spokes. The geometry shows a line where the step used to be at the intersection of spokes to the wheel, but the red highlight confirms this is all one flat surface.
The mesh now seems much cleaner in this area.
In order to attempt and fix the Nonorthogonal cells at the floor caused by the bounding box layer addition cell termination, i have changed my level 5 region refinement to a flat plate, extending over the entire floor of the bounding box.
For some reason the mesh didnt like my region refinement. The thin, level 5 area doesnt even show up. Now im thinking that level 5 cells are too big for a 0.2m thick region refinement.
EDIT
I did the calculation quickly and with a 1m level 0 cell size, a level 5 would be 0.3125m which confirms my mistake. Level 6 would bring the cells to 0.015625m which would work or conversely, I could increase the level 5 region refinement to 0.03125 meters  the better option for me i think.
The amount of Nonortho cells has definitely been reduced. I still need to fix the floor region refinement but that comes in test 8.1. I have also noticed that some of the Nonortho cells have to do with geometry  what i have fixed so far, but others have to do with the cells outside of the geometry  layer addition and snapping processes. These are much harder to change, especially when I am tied to specific boundary layer requirements or total cell count limitations. In the end I may have to accept a certain amount of Nonortho cells.
Wheel test 8.1
 Testing Explicit feature snap
 Correct lvl 5 region refinement height
Checking faces in error :
nonorthogonality > 70 degrees : 348
faces with face pyramid volume < 1e13 : 0
faces with concavity > 80 degrees : 3
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0…1) < 0.02 : 94
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.01 : 2
faces on cells with determinant < 0.001 : 23
volumeRatio
min: 1
max: 364.2708799626919
Now that the correct region refinement size is made the area showed up.
From the side view I now have the bounding box layer addition cells. However, for some reason the region did not mesh over the whole floor even though I set this level 5 region refinement for the exact size of the Bounding box floor. Shown below is the end of this region refinement with level 5 and 4 cells, also with the bounding box layer addition cell that terminates into the ground.
The wheel looks fairly similar with the Explicit feature snapping on. No significant improvement
And where the Bounding box layer addition terminates we have the same problem.
As of now, wheel test 8 had the best results in terms of illegal cells. If I increase the Max allowable Nonorthogonality to 75 then im sure the illegal cell count will drop. This however does not mean the cells are gone, just that the cells between 70 and 75 are now allowed. I do not know how many cells will be “illegal” if I drop the half car simulation down to 70 as well. I also dont know how many cells over 70° will cause problems.
As always simulation is a compromise between many areas. My biggest problem is staying around the 1011 million total cell count for the half car so that i wont have memory problems with the full car sims. This affects the refinement level of surface and region refinements I can apply. If the refinements are not good enough, the geometry will not be perfectly represented, and the snapping and layering processes will suffer resulting in my situation of illegal cells.
This balance is hard to achieve. My goal here is to get to 95% quality so that the results are somewhat reliable. Any feedback from the experienced users would be extremely helpful so that I can be confident moving forward with “X” amount of illegal cells.
Sorry for the long post haha