What you should know about lug nuts

6

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 a 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.

##RVT921

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Richard Starzyk
10 months ago

Hello,
I am an aircraft mechanic and proper torquing of any nut is much more complicated than
this article states. Approximately 24% of torque applied is used to overcome friction between the contact surface of the lug nut and the wheel face and approximately 35% of
torque applied is also used overcoming friction between the wheel stud threads and lug nut threads. Many factors affect this including condition of the surfaces, condition of the threads,
any plating that may not be present, number of times the lug nuts and studs have been torqued, any corrosion (even when none appears to be present) and most importantly lubrication of the threads , lug nuts and mating surfaces.
It is vitally important to clean and thoroughly lubricate mating surfaces and threads to help overcome these friction Induced effects.
Using a calibrated click type torque wrench as stated in the article using the 1/3 method is a good technique and will probably get the torque close to spec, however for any detail geeks
the “torque-angle” or “torque-turn” method is a more accurate method to achieve proper bolt pre-load or torque. Since most torque errors end up being on the low side I personally use the high side of the plus or minus to help overcome friction effects. ( ie 450 FT LBS + or
– 50 FT LBS I use 500 FT LBS)
Happy Travels and Be Safe

DAVE TELENKO
11 months ago

Most larger class “A” motor homes have 22.5″ wheels & some of those lug nuts are torqued in the 400-500 ‘ pounds of torque. Not going to happen with most of us to change out a flat tire, actually most if not all don’t even have a spare! When I had my ’99 Winnebago class “A” it had 16.5 wheels & it was not a big deal to re-torque my lug nuts as I do have a clicker that goes to 250′ pounds, if I remember it was around 150-175’ pounds torque! Also it did have a spare tire & wheel, but no jack or lug wrench.

Impavid
11 months ago

My pick up has hubcaps so when I have tires changed I leave the hubcaps off. I then see the visible lug nuts and re-torque them after 100 miles and then replace the hubcaps.

Ed K
11 months ago

If you use a clicker style of Torque Wrench, make sure you return it to the minimum setting after each use. Other wise the spring inside is kept at a high tension and the wrench will lose it’s calibration and start clicking at a lower torque than you have set in the wrench.

Bill Fisher
11 months ago

One piece of tools I always carry in my truck is a “clicker” type torque wrench and I always check the lug nuts for correct torque before every trip and upon returning. I also check the torque after any service where wheels have been removed from the trailer. A couple of tips: 1) treat your torque wrench with care and 2) always return the torque wrench setting to its lowest setting when done using it. Probably a third should be to have it re-calibrated yearly, but I do not do that because a couple of pounds or so either way will most likely not matter.

Alvin
10 months ago
Reply to  Bill Fisher

Funny how times change. I began my career as a GM tech in the late 60’s when the only torque wrench was in the dealership tool crib, for general use. Only exercised by the rare guy who took the time out of the flat rate time to do a procedure to go fetch the dam thing if they could find it. In the early going I had one of the mechanics help me rebuild a simple 283 for my 63 Chevy. When it came time to torque the heads, Peter went through the procedure, and slapped the valve covers on. I asked him why he didn’t torque the heads, an ask to which he raised his arm in Charles Atlas style and said the torque is in the arm after doing a thousand engines. He was right.

However,I didn’t believe him and the next day I stayed after work and checked the torque, to find every single head bolt was dead on. I took that up with my shop instructor at the Southern Alberta institute of technology, who agreed saying very few old time mechanics ever used a toque wrench, not something that came from their training but the flat rate system of hurry hurry hurry.

I spend 40 plus years in the collision repair side of the biz and never torqued a wheel (or anything else) until well after I retired and started driving new junk with flimsy wheels and rotors and related. Now I’m heeding the babble about torque importance. Because it has become critically important!

I always torque my wheels, certainly not “after every trip” as one person alludes, that’s totally unnecessary. I’ll never trust a wheel shop ever. To many untrained kids…….

How many of you reading this know there’s a torque spec for pretty much every nut and bolts holding your rig together. I doubt many people building them go to the blueprints to find them and use them. Maybe that’s why they fall apart so readily. The old stuff wasn’t like that. Times have changed and we need to change with them. Torque up pal.