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.