Tourqing alum rims

Gee, in my 30 years of working on cars I have never seen a requirement to re-torque wheel lug nuts in an owners manual, had the FSM for my 03 PT Cruiser handy and checked just to make sure I wasn't missing something, no recommendation there either.

FWIW, I am one of those engineers, I developed the torquing requirements for the assembly of the engines used in the F14 & F15 jets as my first assignment out of college so I know a thing or two about torquing fasteners.

I stand by my statement that a properly torqued lug nut will not loosen up under normal temperature changes. I should have explained a properly torqued though. Putting on the nut and tightening it with a torque wrench does not mean properly. The threads must be free of rust, crap, nicks, burrs or any other anomaly that can create friction in the threads. The contact face between the nut and wheel must be in the same condition. Anything less and you can use the most accurate torque wrench made and the clamping force in the joint will be all over the place. Because of the difficulty consistently having the same amount of friction, using a torque wrench to create a consistent clamping force is only slightly better than doing it by hand. That is why torque to yield bolts are used and why race engines are assembled using indicators that measure bolt stretch instead of torque.

A little threaded fastener 101: In order for a threaded joint to stay tight the force generated by tightening the fastener must generate more clamping force than the forces generated due to use, temperature changes, vibration, etc that are trying to force it apart. As long as the clamping force is never exceeded then the joint will stay tight and no motion between the two pieces will occur.

The joint between a cylinder head and block absolutely can not have any motion or the head gasket will fail in short order. With the advent of aluminum heads and iron blocks the need for consistent clamping force across the surface of the head and block to prevent any motion became much more important than it was with iron on iron.

If you look at a torque to yield bolt there will be a section between the end of the threads and the head of the bolt that is smaller in diameter than the root diameter of the threads. This guarantees that as the bolt is tightened stretch will occur in this area. Because its much easier to control this diameter and the metallurgy of the bolt the force the clamping force generated for a given amount of stretch can easily be calculated to a high degree of accuracy. This also provides the information necessary to calculate the clamping force once the bolt is stretched beyond its elastic limit (yielded). So, now you have a number of bolts all generating the same clamping force within a percent or so verse using a torque wrench that can have as much as 20-40% variation in the clamping force for the same torque level.

Not to try and discredit Larry Shepard but he is talking about racing situations where stock parts are being stressed to the ragged edge or beyond. It's very conceivable that clamping forces are being exceed motion is occurring allowing fasteners to loosen. By redesigning the joint with larger fasteners with higher torques for more clamping force the need to retorque is not needed. No uncommon to see drag cars with 9/16 or 5/8 or large studs using correspondingly higher torques.