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Friday, July 19, 2019

Lug nut torque. A critical SAFETY item.

Those that have read their owner's manual, may recall seeing a mention of the need to check the lug nut torque. In this case, we are talking about how "tight" the nuts should be to ensure the wheels stay on our vehicles. Others may have a warning label on the inside of their RV. This is from my Class-C Coachmen.

Note: Class-A and RV with 10 bolt wheels probably require a service truck and torque in the 450 Ft Lb range, so this info may not apply to you as you will need significantly different tools.






First the simple answer:
- Look up the specification in the Owner's Manual.

Here is a sample page from Heartland RV. Note they tell you how often to check and how tight to make the lug ut and even the pattern for the sequence of tightening the lug-nuts.


- With your torque wrench follow the instructions for both frequencies and how tight the lug nut should be.

- What to do if you don't know what a torque wrench is? Watch this video

- What to do if you don't own a torque wrench?
There are a bunch of videos that compare wrenches HERE   But you can get an OK wrench like THIS for $20  or a better quality one like this for $100.   You do not need to buy the most expensive wrench as hopefully you will be only using the wrench a couple times after a tire or wheel was changed on your RV. Or maybe a couple times a year per your Owner's Manual instruction  For infrequent use I have found Harbor Freight non-digital adequate. Just be sure to get a 1/2" as your lug nut torque spec is probably in the 75 to 130 Ft-Lb range. Don't get a wrench that is right at your spec as it will probably have a short life and may not be accurate at 100% of its rating.


Now some background:
Do not lubricate the stud or lug nut with oil. This can affect the torque reading and could lead to stripped threads in lug nuts ($) or broken wheel studs ($$$).

This web site gives a technical background on why not to lubricate lug nuts.


Some Technical Info for those that want to know more:

Torquing a bolt is to get a certain amount of stretch out of the bolt. If torquing a bolt to 80 Ft-Lib, it is technically more accurate to say "When you torque this bolt to 80 ft-lbs, it will cause it to stretch by .0030 inches". In critical applications such as race engines, many engine builders use certified bolts and actually measure the stretch of the bolts rather than using a torque wrench.

Think of the bolt like a spring. When you torque it, you're stretching it so that it exerts force on what you're holding together. This video goes deep into bolt stretch vs torque.

When I was driving my race car, confirming the torque of the lug nuts was MANDATORY before each track session. With this as a standard practice, I never had a wheel come lose in 30 years of racing.

##RVT906




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