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Friday, May 29, 2020

Are your "Nuts" tight enough? Part 2

This topic of how to ensure your Lug Nuts are tight enough, but no too tight,  is a two-parter and this is Part 2.

The first part, if you missed it, covered the Science and Engineering behind the basics as I am expecting that there will be a number of people who will say something along the lines of "Roger, You are all wet. I've done it THIS way for years and never had a problem".

You are certainly welcome to ignore my advice and continue with the methods you have used for years. My target audience is those who are still new to the RV life and do not have years of automotive or mechanical background or training, and those that want to ensure they do not end up with a wheel coming off their RV or breaking a wheel stud.

OK let's jump in.

I am confident that no one wants a wheel of their car, RV, trailer, or dolly to come off while traveling down the road as seen in THIS video. Or maybe even worst to cause someone personal injury as seen HERE. (The man suffered a fractured skull and chest injuries). So what do we all need to do to prevent a wheel coming off one of our vehicles? It's easy. Just make sure all your lugs nuts are properly tightened and neither the wheel or nuts or studs have been previously damaged. Sounds simple enough but how do we do that?

First, you need to know how tight the nuts are supposed to be. This information should be in your Owner's Manual 

You can check out this YouTube How to Tighten "Nuts" - The Right Way. Note: I covered the sequence for setting or checking the torque depending on how many lugs you have on your vehicle in THIS blog post. One important point to consider. If you had service on your brakes or tires and someone else tightened the lug nuts how do you know they did the job correctly? Many of us have heard about or experienced an over tight lug nut so I recommend you set the torque your self as seen in the video. Then when you are doing the recommended "Torque Check" at 50, 100, and 150 miles you will know that you don't have a nut that is significantly over tight. Note if your owner's manual has different mileage for torque check follow your owner manual. If you find a nut that turns after the 2nd check keep an eye on it in the 3rd check and if still turning you need service as something is wrong.

Let's review the tools you will need and seen in the video.
Remember this info is aimed at owners of RVs with tires smaller than 19.5"So if you are in a Class-A you can read to understand what is happening to your "baby" when you call the service truck.

Torque wrench, 6 point socket of the correct size for your nuts, 2' "Breaker bar", 12" long 1/2" drive extension to allow you to get to your dual wheel nuts. Note Trailer owners may not need this tool.
You will probably not need to use these tools too often so top quality (expensive) is not needed so in those cases I head for Harbor Freight for low-cost tools.
Check these links:
1/2" Drive Torque Wrench. Harbor Freight    or  Lowes

1/2" drive extension     Harbor Freight   or Lowes

6 point "Impact" rated socket I recommend you not use a "12 point" socket as they are more likely to spin off or round off your nuts. You do not need to buy a set. You might want to confirm the size by borrowing a socked from a friend or fellow RV owner. Example 13/16"  Lowes
Note it might be better to go to Lowes or similar as you do not need a set, but be sure to get the correct size not something close enough or you can damage the lug nuts. Here is a 3/4" socket from Lowes.

Now how do you get the tight nut off? a 2' long Breaker Bar will make the job easier. This is what I use. and I can easily generate 200 Ft-Lb

OK so with all the tools you may need collected, How do you set your clicker torque wrench to the spec for your vehicle,
Here is a YouTube to help those who have never used a Torque Wrench.

Hope this helps and if these couple of posts help a few RV owners avoid problems we will be happy.


Friday, May 22, 2020

Lug nut Torque? Why is it important and why measure the force? Part 1

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 pick-up 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.

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 is 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.

HERE we learn about SHEAR

Ok, enough "Engineer speak". This stuff is what we engineers learn and use when designing joint 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 s "Clicker" type torque wrench.
We will cover this tool and some others next week.

Stay Safe

You can check out this "entertaining" YouTube from a guy in Australia on How to Tighten "Nuts" - The Right Way