ABSTRACT
Figure 4 shows a release angle study performed on an automotive wheel nut. A tool with a torque and angle sensor connected to the transient recorder is used to loosen the nut, record the torque and angle values, and plot the data. The resulting printed curve shows an extremely high release torque. The high initial breakaway loosening peak torque region is disregarded, as this is simply an indication of the static torque required to start loosening motion. (The high value of release torque is significant from the point of view that it illustrates the high thread friction due to thread pitch distortion on the wheel nut, a factor that helps prevent vibratory loosening on typical wheel nuts.)
The elastic release angle for the wheel nut shown in Figure 4 is approximately 40°. The nut had been tightened to a peak torque of 206 N·m (152 lb-ft), which is 75 N·m (55 lb-ft) greater than the vehicle manufacturer's specification. The wheel nut was originally tightened to a torque of 160 N·m (118 lb-ft), which did not appear to get past the tightening alignment zone as illustrated by the signature shown in Figure 5.
