According to Newton’s third law of motion, for every action, there is an equal and opposite reaction in the physical world. The same can be said for a lot of events, so the impact of installing wheels with the correct amount of torque can definitely invoke the spirit of the famous scientist. As ridiculous as it seems, it’s not uncommon for the instances of loose wheels to increase after abandoning the “good and tight” school in favor of a program that delivers the correct amount of force every time a fastener is tightened.
But the torque wrench isn’t a magic wand that mysteriously ensures every wheel will stay attached to the axle. In fact, the torque wrench is more like an oven. Anyone can set the oven to a specific temperature, but while it is important, following the recipe is essential for success because it depends on the proper amount of every ingredient. In that sense, proper torque is the setting on the oven, and the recipe determines the amount of clamping force.
Every good recipe has a foundation; in this case, it’s technician training. There are a number of different steps that must take place before the torque wrench can take the stage. For example, hub-pilot wheel systems require oil as a lubricant in order for the proper clamping force to be reached at the correct torque. The failure to apply this essential component to the process will result in less clamping force at the correct torque. Several different factors must be in place for each type of wheel or rim system to perform with the correct amount of torque. It takes trained technicians to make sure it’s done the same way every time for each system, and that repeatability is critical for success.
Like every machine or mechanical device, the torque wrench also has a finite lifespan when it comes to accuracy. Proper storage and maintenance can go a long way towards extending the life of a torque wrench or torque device. The best practice, however, is to follow the recommended recalibration schedule so there is documented proof that the tool has been periodically checked and recalibrated when necessary.
Without a doubt, the ingredient that is the most often overlooked or ignored is the torque check following installation. The wheel companies recommend a 50-100 mi. interval, but that guideline is followed so rarely that it might as well not exist. In most cases, a few left- and right-hand turns with a speed bump or two is enough for the wheels to settle in after installation. If there are any major issues, they should be evident after a short period.
The difficulty lies in the situations where a fastener was previously over-torqued to the point that it started to yield but did not break. In these instances, a technician can do everything correctly and use a perfectly calibrated torque wrench, but the wheels still come loose. Since the best way to find a fatigued fastener is to measure the torque shortly after installation, the torque check becomes even more important.
Fleets have come to expect service providers will use torque control devices when installing wheels, but most of them are unwilling to accommodate any type of torque check. Drivers don’t want the hassle and dispatchers don’t want to lose the time, but the folks down in risk management need to understand that in most cases there will be a missing ingredient to the clamping force recipe. And it’s totally up to the fleet to bring it to the table.