Retorquing Wheel Lug Nuts / BOLTS
Jan 6, 2023
Whenever you remove a tire / wheel assembly from the hub, we recommend that you have the lug nuts retorqued between 50 and 100 Kms. Why should a responsible driver do this? The point is road safety. Lug nuts keep a wheel securely attached to the hub, which makes them a vital component of the vehicle. But lug nuts can’t perform as designed without having the correct amount of torque properly applied.
Why Retorque
Torque is the unit of measurement for the twisting force that’s applied to a lug nut. Mechanics will ensure that each lug nut has been torqued to the vehicle manufacturer’s specifications when first fitting a wheel, but a second follow-up check is also necessary.
This is because, after a reasonable amount of time, the lug nuts will undergo the typical stresses and forces of a car in daily use. These stresses include supporting the weight of the vehicle, the rotational effects of driving, cycles of warming and cooling, and nudges from bumps in the road. Such stresses can cause a slight shift in the seating of the lug nuts, which may result in tightening or loosening.
The presence of dirt, sand, rust, or grit between surfaces can also create “false torques” during the initial fitting, where the force applied overcomes the friction but doesn’t translate into clamping force.
Correct Method Is Important
The lug nuts on a wheel are tightened in a specific sequence to provide the proper torque. The correct order for any wheel with five or ten lug nuts is a star-shaped pattern. A wheel with only four lug nuts, meanwhile, is tightened in the shape of a cross. Something else drivers should consider, is whether a shop uses calibrated hand-torque wrenches, which is prefered in order to get a proper torque.
There are, however, ramifications of forgetting or skipping the retorque process. Wheels can come off, brakes damaged, broken and/or stripped lug nuts, bolts and studs.
Over-torquing The first example is a bolt that is loose, with no torque applied — unstretched. The second example is a bolt that is torqued to specification. There is a slight amount of stretch, but not enough to change metal/alloy properties of the bolt and it returns back to it’s original shape and is ready for for retorquing. The third example is typical of an over-torqued bolt. Note that the bolt has not only stretched, but stretched to the point of changing the properties and yield strength of the bolt. The bolt now has a much lower tensile/yield strength and allows the bolt to flex, generate heat and fatigue. A bolt that has been over-torqued will be prone to cracking, shearing, loosening, or breaking off which can result in damage to the wheel and other related components.
Improperly torqued lug nuts or bolts can also result in:
- Warped brake rotors — brakes grabbing, pulsating or overheated.
- Damage to the lug nut seating surface of alloy wheels.
- Wheel hub damage — threaded holes stripped out.
Maintainence
Cleaning Hub Surface A commonly overlooked but important task in the tire shop is to properly clean wheel hubs and studs when changing tires. There’s corrosion that builds up over time in between the hub and wheel and if that’s not cleaned off, you can retorque wheels as often as you want but they won’t set properly, and that’s what causes wheels to come off. It’s not necessarily a wheel torque issue.
Cleaning may come at an extra cost and drivers could ask their garages if they clean mating surfaces before putting wheels back on a vehicle. A thread chaser or tap should be used to remove any burrs or obstructions of the threads allowing the lug hardware to be turned by hand until it meets the wheel’s lug seat. Once lugs are snugged down, finish tightening them with an accurate torque wrench.
