Stop in for a cup of coffee
So I’m gonna use your chart, 1/2-20 are the studs. I’ll torque them to 75
A couple other possibilities, (1) dirt or such in the threads (2) rim not flat against the hub during tightening (which Frank already mentioned one way that can happen).
The whole goal of the torque spec is a tround about way to make sure there is enough spring force created that the fastener will not loosen.
The spring force is my way of describing the tension in the bolt. We're working in the steel's elastic range, and trying very hard not to accidently exceed it (yield point).
We can't measure the tension in the fastener directly, but can make a pretty good estimate knowing the thread angles. But this assumes a clean thread.
Also, if you think about it, this clamping force can not have a softer material or gap in between. If it does, then in use the actual tension on bolt will vary greatly and causing it to loosen even more (or get fretted and shear).
This is why its real important to seat each wheel nut, and then do a light tightening in the start pattern, then do the final torquing.
