RV Tire Safety: Lug nut torque – Part 1: Why is it important?

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with RV tire expert Roger Marble

Here are some YouTube videos on the topic of torque: what it is and how do we measure the force. As an engineer, I sometimes just assume that everyone understands some basic engineering terms, but I am wrong to make that assumption. You don’t have to remember all the details. I am just hoping that when we are done with this topic you will accept our recommendations on how to set and how to check the torque of your lug nuts.

Important info: It is impossible for me to know the size lug nut or specification for every vehicle, but you, the owner, should know this important spec and it should be in your owner’s manual. If you can’t find it, find a dealer of your brand RV or check the on-line forums for other owners of your exact make and model and ask what the specs are. These numbers are critical for the safe operation of your vehicle. I can only talk in generalities in this blog.

One thing to remember is that for Class C and Class B RV motorhomes and for RV trailers, as with your car or pickup with 14″ to 16″ steel wheels, the torque spec is probably between 75 Ft-Lb and 85 Ft-Lb, while 19.5 tires run about 135-145 and 22.5 tires run 450-500 Ft-Lbs. So you folks with large wheels will have to depend on the service truck to tighten your lug nuts. It is possible to get a hand torque wrench with 1/2″ drive sockets that will get you to the 150# to 200# range, but it is probably safer for you to leave the larger wheels and lug nuts for the service tech that has the proper tools. I will address the tools you need next week.

Here is a video that explains what torque is.

Friction is the next topic. Here’s a video about it.

For proper torque of our lug nuts, the stud and nut need to be clean, rust-free, no damaged threads, and no oil lubrication unless specifically specified in your owner’s manual. If you have had problems with a stud or nut, such as a nut coming off, or broken stud, or the wheel being partially loose, or the threads have been cross-threaded, or the nut was significantly over-tightened, both the stud and nut should be replaced. Over-tightening can get the stud into the “yield” load range which can lead to incorrect tightening and even to stud failure.

This video shows why nuts come apart.

“Transverse vibration” is what happens with a wheel fastened to a hub. This is why we need to check torque to be sure the assembly is retaining it’s clamping load after we start driving.

Tensile strength is covered in this video.

In this video we learn about shear.

OK, enough “engineer speak.” This stuff is what we engineers learn and use when designing joints and developing specifications for studs and lug nuts. There is no test in my blog on this topic, but if you are going to argue with an engineer, then you will need a solid understanding of these forces.

Now, the next step is for you to do a little research.

A. Find your owner’s manual and look up the specifications for each of your vehicles.

B. Make a note of the torque spec and lug nut size where it is easy to find. A permanent marker on your door jam might be a convenient location.

OK, here is a short video on using a “clicker” type torque wrench.

We will cover this tool and some others next week.

Stay safe.

 

Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.

##RVT949

 

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Nick Spence

I noticed that there are battery powered impact wrenches for a very reasonable cost. Looking at them, I see a number that go well over the 450 lbs of torque my wheels require. Will they really do the Job? Here’s a link to just one at Lowe’s that claims 650 ft lbs: https://www.lowes.com/pd/Kobalt-24-Volt-Max-1-2-in-Drive-Cordless-Impact-Wrench-1-Battery-Included/1000061641 Thanks for all the time you take educating us.

Steve

I’ve seen advocates of using grease (bearing grease) and not using grease on studs. Can you chime in on this matter? Thanks

Alain Tasse

This is very interesting but…as everything in the mechanic’s world, not only on rvs but also in the auto and truck worlds, the absolute mantra still is: “it will do”. For years I’ve had an uphill battle every time tires need rotation on my Suburbans, even at GM dealers, where I litterally have to give the “tech” a drawing of the pattern the owner’s manual calls for which is “rearward-cross” on most rear or four wheel-drive trucks. Just to be on the safe side I go the extra step and warn them that the tires are marked. Would you believe, that once in a while, I still have to get the job redone to get it right.

As for “torquing” wheels, especially on travel trailers, I just love the loud whizzing tunes those shop air guns sing. I always have to laugh when, after a bearing or brake job on the trailer, I see the mechanic’s or service advisor’s look on their face when asked: “and at what torque did you drive the lug nuts?”. That’s when you see that “until death do us part” lights up on their foreheads and that no other spoken words can be trusted from that point on. Experience erodes trust and that’s only one of the many problems that appear when getting old and you can no longer do the job yourself. Looking forward to next week’s article. I just might re-invest in a few good tools and “torque the heck out of everything” myself.

Dan

Very good video. He might have explained how using the torque stick works with the impact wrench. It vibrates when it reaches its determined torque and doesnt let you over tighten the lug nuts. For RV rear wheels that are deeply dished you will need an extension on your torque wrench to reach the lug nuts. Putting an extension on a regular ‘clicker’ torque wrench distorts the accuracy of the clicker and there is a formula for adjusting the amount of torque needed. That;s why the simplest way to torque lug nuts is with an impact wrench and a torque stick. The stick will cost you about $30-$40. A usable battery powered 1/2 inch impact wrench will cost you around $100-$150. A corded 120 volt ac impact will be even a lot less. You’ll thank yourself for getting those if you ever have to change a tire on the side of the road. Better yet, get AAA.