[03kbredfire]

I thought this might make for an interesting discussion topic, but reading another thread indicated that the 14 mm wheel studs on the 2015 up S550 "requires" 150 lb ft of torque. Interestingly enough, that is the same stud size and torque spec for my F-150. Now I'm not an engineer, but I've taken more than a few engineering courses in college while figuring out my future career, so in my mind I think it's overkill, so I'm going to argue against said requirement.

First off let's start with every generation of mustang prior to 2015. They all came with 1/2-20 wheel studs and lug nuts. Torque specs range between 80 to 105 lb ft. Bolts come in varying grades and has to do with the strength of the bolt and how much clamping force it can exert. SAE has a different grading system than metric, but the higher the grade, the stronger the bolt. For each size and grade there is a maximum torque specification. Even that is skewed by whether the bolt is coated or lubricated. I'm sure specs vary slightly depending on the source, but the variance should be minute. The source I'm using comes from Fastenal's website.

For a 14 mm bolt with a 10.9 classification (grade) shows a maximum dry torque spec of 148 lb ft. The lubricated spec is 111 lb ft. Both would yield a clamp load of 16,154 lbs. If we drop down a grade class to 8.8 for 14 mm bolt, the torque spec dry and lubed is 104 and 78 lb ft, respectively. The clamp load at that spec is 11,289 lbs.

Looking at the old standard, the 1/2-20 in grade 8 has a maximum torque spec for dry and lubed at 120 lb ft and 90 lb ft, respectively. Dropping down to grade 5, we see specs for dry and lubed at 85 and 64 lb ft respectively. The clamping force for grade 5 and grade 8 are 10,197 lbs and 14,396 lbs, respectively. I'm not sure why the maximum torque spec for the mustang doesn't go to 120 lb ft, unless the stud is not quite up to grade 8 standards. The point being the max torque spec is probably yielding a 12,000 lb clamping load, give or take.

Granted I don't use a torque wrench to tighten my wheels, but I don't use an impact either. I've taken the wheels off my truck quite a few times and I seriously doubt I'm tightening these nuts much more than 100 lb ft. When I've removed them they're always tight. I guess one of these days I'll get out the torque wrench and figure out how tight I'm going.

It just seems to me Ford is using a torque spec that is in the maximum safe range for the fastener and that a 14 mm stud (.55") might be a little overkill in a 4,000 lb car. They are using a 6th stud in the truck line too. That's not to say I would recommend something less than 150 lb ft of torque if I tracked the car.

If someone has different insight, I'd like to hear it.

A lot of this torque spec depends on the thread pitch. As far as I can tell, the thread pitch on the newer s550's are a 1.5mm. This would equate to around a 17 thread per inch. Because the thread pitch is more coarse than the past 20 thread per inch, then a higher torque is required to net the same clamping force. It is integral to the equation. If it was a finer thread pitch, then you would not require near the amount of torque to obtain the same result. So as a result you have a larger bolt with a coarser thread than the older 1/2X20 studs. Yes, 150 sounds right.

 

[03kbredfire]

Why could you not use 120 lb ft (feel free to use a torque wrench) for the 14mm wheel stud when it provides as much clamping force for the wheel as the previous 1/2" stud post-2015?

How did you come up with the same clamping force for these two?

 

[03kbredfire]

Perhaps reading the initial post will provide a clue.

This post seems quite belittling when I was being very sincere.
There is a lot of info in the original post and I saw the 16,154 for 10.9 and 14,396 for the grade 8. I asked because this shows a greater than 10% difference between the two clamping forces. Maybe the roughly 10% difference is considered as being the same. I was looking for the information on various engineering reference documents and assumed I had missed something. Anyway, I was trying to help the conversation. This is starting to look like a good ol' boys club. Newer members may not be very welcomed here. I do not really know how to take your response as anything other than belittling. You could have just answered the question. No one needs to be on any given site. We choose to provide info to others in need. I will stick with my previous response of 150 lb. ft. as being the appropriate torque spec. It is not only about the "girth". It has very much to do with the slope or pitch of thread. If the thread pitch was as fine as the 20, then a much less torque force would be required to net the same clamping force. Hopefully I am reading into your reply wrong.

 

[03kbredfire]

We have had a BUNCH of new members join the forum over the last couple years. We strive to make everyone feel at home here and keep the crap you find elsewhere on the internet off this site. Old members or new members, this is a place to hang out and chat about these fine automobiles. There will always be differences in opinions, but you won’t find the name calling and outright attacks here like found elsewhere. Those people are shown the door in short order.

I kind of doubt you will show the door to a member with 7,000+ posts. I hope there was a mistake in intent for snarky post given by member or that I read the post as snarky unfairly. In either case, I appreciate your quick reply.

 

[03kbredfire]

Be careful using a torque wrench at its maximum setting. Each brand sets their measurements at a min and max value with an accuracy of 5% give or take. However, when you max out a torque wrench you can overstress the internal mechanism and throw the accuracy out the window. When I was aircraft maintenance in the Air Force our tech data said to never exceed max torque value minus 10%. So if something needed 150 ft/lbs of torque we used a wrench that went to at least 165 to account for errors induced by heat and humidity. (Usually a 250 ft/lb as no one makes a 165 lol)
But, that being said, that’s why there is a +/- value in the manual, to help account for tool error and ambient conditions.

Excellent advise. All of my torque wrenches have been verified at a calibration lab to meet a standard of + or - 5% for my liking. I have them checked up and down the range that they are indicated for being used at. If I can add on to this. Try to not leave torque wrenches at the setting used after they have been used for intended purposes. Dial them back to a number at or lower than 10% of there full range. They are typically utilizing a spring for the breakover mechanism. This spring can stretch if left at at higher rating over time and loose some of their accuracy.

 

[03kbredfire]

Tone and intent is not always easy to read on a screen.

Fair enough. I try to supply very detailed and accurate information. I will dig into a given subject to attempt to help when I have background that I feel can help a given topic. Sometimes a well thought question is just as good as a well thought response. I also understand being frustrated and having a bad day.

 

[03kbredfire]

Good stuff Terry. For what it’s worth, I have had to nuke a few long standing members through the years. Members that don’t play well with others find their way out one way or another. John (catmonkey) has good intent. He enjoys digging deeper on subjects here.

That’s what this forum is all about. Car nuts talking about cars... sharing info and having fun along the way.

That is one reason I preferred to be more engaged in this site. Sharing good detailed information. John has provided a great deal of this kind of information. I will as well. I will try not to use "re-read my post" or "get a clue" to others as it is very off-putting. Low post count does not mean less worthy. Not a good feeling to oust a member, I am sure. I am not as good a source as a John Mihovetz, but I am O.K. I say that because he does not post much either. When he does, I listen. 🍻