The consequences of improperly tightening or not tightening lug nuts enough are obvious - the wheel comes off at an unexpected moment. Not much imagination is needed to see what happens next, and none of what will happen is good.
So people have a tendency to go the other way, to tighten lug nuts as much as possible. You have probably heard the phrase "Tighten it until it breaks, then back off a half-turn."
All joking aside, over-tightening can be as unsafe as under-tightening. Over-tightening stretches the stud or bolt, which weakens it. It may no longer hold the lug nut securely, or, in the best-case scenario, it will break when the wheel is being removed.
Best Practices for Lug Nut Reinstallation
A shop or service garage will remove and reinstall the lug nuts with an impact wrench, which is a tool that is powered by compressed air to expedite installation or removal of almost anything that has to be screwed on or off. In professional shops, the torque setting of these impact wrenches is set below the level of tightening required for that particular job.
If you watch closely while a career technician at your local shop rotates your tires, or is replacing the tires after any other service such as brake work where tire removal was required, you will see as a final process a hand tool called a "torque wrench" being used to verify that every lug nut is tightened to the proper "torque" or degree of tightness specified by the manufacturer.
How Do Torque Wrenches Work?
Torque wrenches must always be used to finish the tightening procedure if the tightening is to be accurate. In its most basic form, calibrated torque wrenches will click when they reach the specified, preset torque number. This is an audible and sensory signal to stop tightening - you can feel the click, even in a loud shop environment.
Because proper lug nut torque is so important, many shops use a check system whereby a second technician or a supervisor uses a torque wrench to verify that all the lug nuts have been properly tightened to "specs." And that specification can be from 62 foot-pounds on a Suzuki Aerio to 165 foot-pounds on many Ford pickups. The vehicle manufacturer has determined the proper specification in all cases.
Lug Nut Torque: Surprise Your Technician
So, the next time your vehicle is serviced, surprise your favorite tech. Ask him to tell you what the "torque-spec" is for your lug nuts. And then thank him for keeping your vehicle as safe as possible.
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