Torquing Lug Nuts
| 30 April 2003
Although some shops adhere to manufacturer’s lug nut torque settings when they install wheels on your car, lug nut tightening is still relatively haphazard. It shouldn’t be because safety and part’s longevity can be adversely affected when lug nuts are tightened incorrectly. For years, I’ve made it a practice to loosen wheels installed by a shop (any shop) and then hand tighten them to the correct torque specification.
Forget what the NASCAR pit crews do on Sunday afternoon. They’re fighting the clock and besides their wheels (in fact, their whole car) is disposable. I’m sure you don’t look at your car as a disposable item so let’s talk about the “what”, the “why”, and the “how” of torquing lug nuts.
First, the “what.” Lug nut torque is measured in foot-pounds (ft.-lbs.) but you don’t need to understand or even know a definition of torque to apply it to your car. But if you need/want a definition, here’s one: torque is equal to the magnitude of the component of the force-vector (measured in pounds) lying in the plane perpendicular to the axis (of the lug in this case), multiplied by the shortest distance between the axis and the direction of the force component (measured in a unit of length such as inches or feet).
The “why” can best be explained by realizing that lug nuts need to be tightened evenly so the stress they impart to wheels, hubs and, brake drums or brake rotors is evenly distributed. When stress isn’t evenly distributed, wheels can bend or break, brake rotors or brake drums can warp, and wheels can fit unevenly on the hubs. In worst-case scenarios, loose lug nuts can allow a wheel to wobble or even fall off. If they're too tight, the lugs themselves can break off the next time you try to remove the nuts. Improper tightening can cause wheel vibration and the warped rotors/drums mentioned above result in chatter when the brakes are applied.
When it comes to the “how”, you need to know the lug nut torque spec. for your particular car and you need a torque wrench. Sometimes the torque setting is in the owner’s manual. If not, you can get it from the dealer, a shop manual, or a tire store. A non-vehicle-specific torque table based on lug diameter and shown for illustration only is at the end of this column. Don’t use the values in the table in place of manufacturer’s specifications.
Torque wrenches are available at auto supply stores and department stores that carry decent tool selections. Buy one with a 1/2-inch drive that reads to at least 150 ft.-lbs. Check the wrench-packaging to make sure the accuracy is no worse than + 4%. Some inexpensive wrenches have accuracy in the + 10% range; they should be avoided. Also buy a 6-point semi-deep 1/2-inch-drive socket to properly fit your lug nuts and a 1/2-inch drive 6-inch extension.
Torque specifications are usually given as a range. Plan to tighten the nuts to a setting equal to the maximum of the range minus 1/3 of the range. For example if the range is 85 to 100 ft.-lbs., tighten them to 100 minus 5 (1/3 of 15=5) or 95 ft.-lb. Here’s the step-by-step for use on each wheel. It is assumed that the torque wrench is a break-away type:
1. Install all nuts by hand to make sure they aren’t cross-threaded. Make them hand-snug and be sure their tapered surface is properly engaged in the tapered surface of the wheel.
2. If the maximum torque spec. is 100 (or less) ft.-lbs.:
- Set the torque wrench to 60% of range-maximum and tighten th
e lugs in the sequence shown in the diagram. Following the correct sequence is just as important as using the correct torque. - Reset the wrench to the value calculated from range-maximum minus 1/3 of range and finish tightening the nuts using the proper sequence.
3. If the maximum torque spec. is more than 100 ft.-lbs.:
- Set the torque wrench to 40% of range-maximum and tighten the nuts in the correct sequence.
- Reset the wrench to 80% of range-maximum and tighten the nuts in the correct sequence.
- Reset the wrench to the value calculated from range-maximum minus 1/3 of range and finish tightening the nuts using the proper sequence.
The procedure sounds cumbersome when it’s explained but in practice it’s easy. And it’s an important consideration whenever wheels are R and R’d. If you have alloy wheels, either factory or aftermarket, the procedure should be considered mandatory.
There’s one more step that should be adhered to. After driving 25 to 50 miles and then again after 100 miles, all lug nuts should be checked at the setting used for the final tightening. Check them in the sequence shown in the diagram. This is particularly important when the car has alloy wheels.
A non-vehicle-specific torque table based on lug diameter follows. The table is a general reference only. It does not replace the manufacturer’s wheel-tightening specification.
Lug Size Ft-Lbs Torque
7/16” 55-65
1/2” 75-85
9/16” 95-115
5/8” 135-145