Why does this keep happening to my studs?

[puptwin]

Why on Earth would they have left hand threads?

Left and right hand threads have been common in the heavy truck world at least through the 1980's. The requirement for LHT has to do with rotational forces acting on the nut combined with variable loading the wheel encounters during normal operation. I don't know the machine dynamics driving the process but the fact that the tapered wheel nut serves to pilot or center the wheel onto the hub makes this interface critical and more susceptible to backing off. The solution is to have the nut tighten in the direction of wheel rotation.

Heavy trucks have moved away from stud-piloted to center-hub piloted wheels utilizing traditional right hand nuts with captive washers at all wheel locations. Again, the requirement for threads and hardware to be clean and dry during installation is called out. Torque values are typically 450 - 500 ft-lb. It's shocking how many tire shops continue to install these wheels with 1-inch drive impact wrenches. We've had trucks come to us directly from a tire shop with lug nuts tightened in excess of 1000 ft-lb. It's amazing how little attention is paid to such a critical component.

 

[oldschoolskier]

Few understand how bolts maintain tightness. It is by tension, in the elastic range if the steel stress strain curve which is very large compared to some materials. The bad point is at the upper limit it turns to material hardening and sudden failure. Over torqued or over stretched puts it in that sudden failure range with a little extra load.

All this makes logical sense but until you see it happen in a test cell does the point get driven home (civil engineering materials lab 3rd for me).

 

[scott43]

I've broken many bolts and it's very predictable. The resistance to tightening is obvious in that it becomes easier to tighten as the material approaches failure as you exceed its strain limit

Also precession is the effect that left hand thread can sometimes counter.

 

[slowrider]

When you drive a 105,500 GVW, 8 axle, 30 tire class 8 truck over the Cascades you check your lug nuts.....every single one, more than once a day. It's your ass in the seat.

 

[scott43]

When you drive a 105,500 GVW, 8 axle, 30 tire class 8 truck over the Cascades you check your lug nuts.....every single one, more than once a day. It's your ass in the seat.

And quite frankly if you lose a wheel you can easily kill someone. Happens oftenish here..

 

[slowrider]

And quite frankly if you lose a wheel you can easily kill someone. Happens oftenish here..

Exactly. Part of the responsibility of a professional driver is to ensure your vehicle is safe to travel on the highway and not to endanger other motorists. It's unfortunate that everyone doesn't think this way. [Off the soap box.]