No spacers means no effects of them on the hub bolt connections !
In my previous posts I was trying to find an explanation for the broken hub bolts as reported by the reviewer, mentioned in post #3, when spacers are used with standard torque setting an no locking compound on the hub bolts. Here some factors of influence.
Operational loads on hub bolts depend on cornering direction, wheel position (front, rear axle and driver-side, passenger side) and vary during the wheel rotation (top or bottom position of the bolt in the ring of hub bolts). If you torque them equally, they all have the same pretension load. The driving wheel torque, which we all love so much from our M5, is normally delivered by the friction forces (all working in a direction tangent to the hub bolt circle) between axle hub/ (spacer/) wheel hub. In the sidestep below, about friction, you can see that if the contact is not dry/ clean the factor is lower and if transverse loads on the wheel during heavy cornering 'eat up' part of the axle-hub/ wheel-hub contact force, less contact force remains to generate friction load at that hub bolt. If friction load is reduced to a level less than the transverse load each hub bolt has to deliver for the drive wheel torque, then the hub bolt cross section has to support the rest. It is then loaded by a shear load. The combination of tension load plus shear load is more severe for any bolt or stud. They are able to support this combination of loads (always with a bit of torsion stress, due to the torquing), up to their ultimate limit.
Adding spacers to a wheel, increases the eccentricity from the contact area-center on the road to the center of rotation (seen in an axle vertical cross section plane), somewhere in between the wheel bearings. Depending on the direction of the turn (see left or right turn below) and a wheel sitting on drivers side or on passengers side, some hub bolts feel a relief of their tension load because of this, while other hub bolts have a higher load to carry.
Less torquing of hub bolts may sooner lead to friction not helping the bolts enough and thus in larger shear loads on the hub bolts. Using spacers without using a locking compound increases the chance of hub bolts loosening. Normally, without spacers, the conical bolt heads provide sufficient friction (if installed dry of course) to prevent this from happening. Less bolt pretension load plus variation in load staying the same (only depending from driving/ cornering conditions) means higher chance of wheel-hub + spacer reaching the start of their reaction curve. If this start is reached (meaning spacer- + wheel hub-compression force is zero), a jerky hub bolt force occurs. In the worst case this may lead to failure of a hub bolt due to fatigue. And in this matter hub bolts behave just like sheep: If one goes, more will follow ... :frown
Your wheels provide control over where you're going. I would never cover up something there. Using a bit higher torque setting and adding Loctite to your hub bolts or studs and stud nuts could just regain some of the safety, that was offered by adding spacers ...
Side step - Friction force
Friction force = factor * contact force. Factor is the coefficient of friction, depending from the contact conditions. Dry/ clean = 0.15 (-), greased = 0.05 (-), oil film = 0.0xx (-) in big end bearings. Contact force = how much the two adjoining surfaces are pressed together. Never grease the surfaces of wheel hub (or flange on the front wheel) and inside of the wheel. You may grease the center ring (the wheel hub may seize on it) since it hardly contributes to the friction loads.
Side step - Left or right turn
In a right turn the tension load in every hub bolt on top of the wheel on drivers side wheels is increased (as is on bottom side of the wheel hub bolts at passenger side wheels), the hub bolts there stretch more, spacer and wheel hub are compressed less and thus the contact force between axle hub and wheel hub (or spacer, if present) reduced. In a left turn top and bottom position + drivers side and passenger side have to be exchanged in the expression above. Every bolt changes position many times per second and so does the contact force: real dynamic loads.