By Russ and Tiña De Maris
Here’s an area of RV tech that few of us give much thought to — until we have a flat tire on the road. These characters play a critical role in RV safety, yet often get little more than lip service. Here are some thoughts and tips on dealing with lug nuts.
Lug nuts and their mates, the lug studs, are designed to be torqued to a given point. The nut and stud, when put under twisting pressure (loosely translated “torque”) actually stretch a bit. When the pressure is taken off, the metal snaps back, allowing the nut and stud to mate. One technician describes this process as a sort of welding that can later be taken apart.
So what happens using the “quick and dirty” method of just jumping on the lug wrench or slamming the lug nut with an impact wrench until that clattering noise stops? Likely you’ll have a lug nut that’s either too tight, or too loose. Either one can lead to problems — even to disasters. Too loose, the wheel’s bolt holes can be scoured and create damage, unwelcome vibration, or uneven tire wear. Too tight, the stud can be stretched too far, weakening it; and if on a wheel equipped with a spindle, the spindle itself can be damaged. And in the catastrophic category, too loose or too tight can actually lead to the old “drive ’til the wheels fall off” scenario.
SO WHAT’S TO BE DONE?
When you, or your tire technician, put a wheel back on your rig, the lug nuts should always be torqued to the right specification. The process is simple: Lug studs should be free of dirt and dust and the wheel put in position.
Using an impact wrench or standard lug wrench, snug up the lug nuts. Now use a torque wrench to do the rest of the job. A “clicker”-type torque wrench may be your best bet. Here the wrench is set to the number of foot pounds desired, and when that specification is reached the wrench clicks, giving an audible acknowledgment. Dial-type torque wrenches are easily damaged by being dropped or tossed around, and can go out of calibration easily.
If a clicker-style torque wrench is used, put the socket on the lug nut and apply steady, even pressure. The nut should turn at least a quarter turn before the “click” is heard. If the nut doesn’t move but the wrench clicks, it indicates the lug nut is already too tight. Back it off and reapply torque to get it right.
It doesn’t hurt to check your lug nuts to make sure someone hasn’t already “goofed them up.” Thread the lug nut onto the stud by hand. If there are irregularities in how the nut threads on, you’ve found indications of “bottlenecking,” meaning that the stud diameter is a little smaller. Somebody’s over-tightened the lug nut before. It’s best to replace any stud that shows bottlenecking.
After you’ve torqued the nuts and put the rig back in service, it’s always wise to recheck the torque after driving a few miles. Things can happen that can cause you to find the torque on the nuts “off” after a little while. A bit of a hassle, but a lot better than losing a wheel!
Got chrome lug nuts? These can be handled in the same fashion, but here’s a tip to keep them from getting dinged up in the process. Make sure the lug nuts are clean and free of dirt and grit. Cover the lug nut with a section of plastic freezer bag while tightening — this keeps from direct metal-to-chrome contact. Be sure to use a “fresh” section of freezer bag over each lug nut.
Finally, where do you find the proper torque specifications for your lug nuts? Check your rig’s owner manual or contact the company’s tech folks. If you’ve got an orphan RV and no owner manual, here’s a link to tirerack.com with suggested torque specifications based on lug nut size.
And a final note: After posting this story, a sharp-eyed reader, Martin Stein, wrote to us about his experiences as submariner. When checking lug nut torque, it’s a good idea to do it in a series of steps. Set your torque wrench to a third of the final specification, then following a star-pattern, go around the wheel and set each nut. Then adjust the wrench to two-thirds of the final value, repeating as above. Finally, set the wrench for the specified completed torque, and complete the job with one more round. It’s a bit fussy, but will ensure a much safer job! Thanks, Martin, for the reminder!
photo courtesy modenadude on flickr.com by creative commons license
Updated 2019/11/11 1146 PMT, adding information on three-stage torque check.