Wheel Lug Nuts Have a Safety Torque Rating so your Wheels don’t leave you in traffic!

I love people who change tires or use pneumatic guns to take off lugs on any units, cars, trucks buses or even trailers.  And somewhere in the master skills of changing tires or having repairs a 100 km down the road your wheel leaves the unit or in your walk around the nuts are loose.

Proper installation requires torqueing wheel-attaching hardware (lug nuts or bolts) to the recommended specification for the vehicle make, model and year. Torque specifications can be found in the vehicle's owner's manual, shop repair manual, industry reference guides or obtained from the vehicle dealer. 

In the USA alone never mind Canada, Wheel detachments occur at an estimated rate of 40 to 60 per week in the U.S., resulting in about 20 reported accidents per week. Studies in both the U.S. and Canada have indicated that about 45% to 50% of these wheel separations are caused by loose wheel nuts.

Those separations which do not result in accidents can still be expensive. The total costs for an extended road side service call, the driver/vehicle downtime, the replacement of a wheel and/or hub and mounting hardware, and a tire if the wheel is lost, can be substantial - not to mention the potential for late delivery penalties. And fines for wheel separations can be stiff in some regions - for example, up to $50,000 per separation in Ontario.

The wheel separations which do result in accidents can create devastating consequences, sometimes maiming or killing those involved. The majority of these accidents result from the detached wheel bouncing along the highway until it impacts oncoming traffic. A small percentage result from the detached wheel hitting pedestrians, or causing the vehicle itself to overturn.

Proper torquing requires using the correct tools, procedures and patterns to prevent over-tightening hardware, stripping threads and stretching studs, as well as will reduce the possibility of warping brake drums, brake rotors or suspension hubs.

Both undertorquing and overtorquing are common when air impact wrenches are used because the actual torque that gets applied depends on so many variables. A common approach is to purposefully overtorque wheel nuts, in part to combat this variability and in part based on the reasoning that "more is better". However, overtorquing actually reduces (not increases) clamping force in many cases, by stretching the studs or threads beyond their ability to respond - especially when this is done repeatedly. Overtorquing can also cause other problems such as cracked, seized, or cross-threaded nuts (which cannot apply the appropriate clamping force), and increases the frequency of stud failure and cracked wheels.

Differential thermal contraction can occur when wheels are mounted at shop temperatures in cold climates. As the wheel components cool to ambient temperatures, clamping force is lost. Wheel nuts which experience any rotation (i.e. back off) during this time will not regain their original torque / clamping force values.

Improper mating surfaces include both damaged and contaminated mating surfaces. Proper clamping force cannot be achieved with non-flat mating surfaces such as damaged or bent hubs and wheels, or worn or elongated bolt holes (raised metal). Contaminants such as excess dirt, sand, rust, metal burrs, and paint on mating surfaces can wear away with use, causing a settling effect. When present on the threads or between a nut and the wheel surface, these contaminants can also change the clamping force / torque relationship, resulting in "false torques" where much of the torque applied is used to overcome friction and is not converted into clamping force.

A loose wheel nut can originate from any of these sources individually, or more probably, from a combination of these sources - which makes the task of eliminating all loose wheel nuts very difficult.

Under- or over-tightening wheel-attaching hardware can be damaging and dangerous.

Torque specifications are for dry threads only. The fastener threads should be free of oil, dirt, grit, corrosion, etc. The hardware should turn freely without binding when tightened by hand. It is important NOT to lubricate hardware threads or seats. The friction at which torque is measured against should come from the hardware seats. Lubricating hardware threads and seats alters the friction generated at the lug seat which will result in inaccurate torque readings and/or over-torquing of the hardware.

So what charts or standards did they use and NO NOT ALL UNITS AND LUGS are the same or same tightness, just like this chart for example,  https://jameshalderman.com/images/lug_nut_chart.pdf  or sites like, https://www.discounttiredirect.com/infoCenter/infoWheelTorque.html .

Do the shops use proper charts and up todate data for your safety.

We do not recommend using impact guns or torque sticks when installing wheels.

Impact guns deliver torque as torsional impacts, made by internal hammers. Delivering torque as torsional impacts can damage hardware and wheel finish. Some vehicles, such as Porsches, require the use of special sockets to tighten the hardware without damaging their anodized coating.

The proper application of a torque stick requires the use of a lower valve torque stick than the vehicle's specified torque setting first. Only then should the hardware be tightened to the final torque setting using a beam or click-style hand torque wrench. Often this critical step in the procedure is overlooked and the result is inaccurately applied torque on the hardware.

Some of the variables that can cause inaccurate torque delivery:

·        Type of impact used (air, electric, cordless)

·        Power (air pressure, air volume, length of hose, size of fittings, battery power, battery age)

·        Impacts per second

·        Size of internal hammers

·        Possible use of additional adapters

·        Socket size, weight, length

·        Operator grip strength

·        Weight of the impact

·        Applied angle during use

Attempting to fully tighten hardware with impact guns/torque sticks also prevents using a click-type torque wrench to confirm the specified amount of torque is present. While a click-type torque wrench can identify when the selected torque has been reached, it cannot diagnose excessive torque.

Once you have the right tools, use the appropriate crisscross sequence (patterns shown below) for the number of the vehicle's wheel-attaching hardware positions until all have reached their specified torque value.

New wheels should be re-torqued after the first 50 to 100 driving miles.

This should be done in case the clamping loads have changed following the initial installation due to the metal compression/elongation or thermal stresses affecting the wheels as they are breaking in, as well as to verify the accuracy of the original installation.

When rechecking torque value, wait for the wheels to cool to ambient temperature (never torque a hot wheel). 

When you detect or not a problem on your tires or wheels what are you using in safety to say OK what is the root cause and corrections!

Over-tightening a flat-seat nut can deform the wheel, causing the aluminum under the washer to extrude, which displaces the aluminum, causing the nut to loosen.

Over-tightening can also stretch the wheel studs or wheel bolt shanks beyond their elastic range. All bolts or studs are designed to stretch a miniscule amount when optimal clamping load is achieved. This elasticity of the stud or bolt is what helps to secure the wheel on the hub. When torqued to specification, this is referred to as achieving the proper “clamping load.” If the stud or bolt is excessively over-tightened, it’s possible that it will stretch beyond its yield point, losing its “rubber band” effect.

If stretched beyond the yield point, the stud or bolt becomes so weak that it cannot provide the clamping load needed. The result: The fastener loosens or the stud or bolt shank breaks.

Always follow the torque specifications listed by either the vehicle manufacturer or by the wheel maker.

Don’t guess. Actually take the time to pick up a calibrated torque wrench and tighten all of the wheel’s fasteners, in the proper sequence, in several steps to achieve final (and equal) torque values.

As far as thread preparation is concerned, make sure the threads are clean and free of dirt, grease, grit, etc. As far as wheel fastening is concerned, specifications are generally listed based on dry (no lubricant) threads.

Wheels are subjected to a variety of forces, including vertical forces from the vehicle and its cargo, road vibration and shock forces, cornering forces when the vehicle turns, and rotational forces from the turning of the wheel, especially during acceleration and braking.

When a wheel nut loosens these forces are redistributed among the remaining nuts and studs, but preferentially to the nuts and studs adjacent to the loose nut, causing these nuts to back off at reduced wheel force levels. This loosening process accelerates with each successive nut that loosens, as the total clamping force drops and the stress concentration at the remaining nuts and studs increases. At this point these studs can fracture due to fatigue or overstress, accelerating the process further - especially with heavy cargo loads.

When the wheel forces exceed the clamping force of the remaining nuts and studs, the wheel will move relative to the hub which results in side loading and loosening of the remaining nuts, bending fatigue failure of studs, elongated bolt holes and wheel pilots on the hub, fretting fatigue cracks between the bolt holes, and wheel separation if not detected quickly.

The rate of this process, and thus the potential for detection prior to wheel separation, depends on the type and magnitude of the wheel forces being experienced.

Loose or missing wheel nuts, and the wheel and component damage caused by them, can result in both fines and impound. Penalties vary from "points" and a few hundred dollars to several thousand dollars and 15 days impound for first offenses, with much stiffer penalties for subsequent infractions.

Wheel, hub, and mounting hardware damage caused by past loose wheel nuts or overtorquing greatly increase the risk of future loose wheel nuts and wheel detachments, and should be corrected. Repair or replacement can easily reach well into the hundreds of dollars when considering both part cost and the labor involved.

In addition to the direct costs for inspection infractions and wheel/component damage, downtime is required to correct these problems. If not corrected in the shop, the downtime for both vehicle and driver can extend to several hours and result in road call charges while the driver or inspector waits for the problem to be corrected. These charges also can reach well into the hundreds of dollars at typical hourly downtime and road call rates.

Collectively, the total cost of a single event caused by loose or missing wheel nuts can be substantial. This is especially so if the event results in a missed delivery time, the penalties for which can sometimes reach into the thousands of dollars per minute range.