I should have continued from clamping load to stud stress:

With 15,000 pounds of clamping force, which results from 140 ft-lbs of dry or plain torque, The stress on the bolt is the clamping load divided by the cross sectional area of the stud.

The area is 3.14/4 x (d)exp2 or stated, pi divided by 4 times diameter squared. For a 9/16" diameter bolt the area is 0.248 square inches.

15,000 pounds/ 0.248 square inches is 60,391 pounds per square inch or psi.

30,000 pounds of clamping force which results from the same torque applied to a lubricated stud doubles the stress too.

30,000 pounds/ 0.248 square inches is 120,783 psi

Yield stress for most studs is around 100,000 to 110,000 psi. Exceeding yield stress in the bolt causes permanent stretch that does not come out when the load is released. Further the clamping load cannot be ensured from the spring like action of the stud once it's been stretched out. The stud is no longer able to provide that clamping load and can become loose. Once the stud has been "strain hardened" it's trash and needs to be replaced.

BB2

 

Wheel studs on Ford vehicles are are/were a tempered grade 8, minimum yield for tempered grade 8 is 130,000 PSI.. The metric ones are Grade 10.9 similar to (actually a little better than) grade 8.

 

Thanks for that definitive info. I was looking for the listed yield for the lugs specified on our trucks and couldn't find it, so I posted the approximate values. Regardless engineers use safety factors and for tension it's usually 60 percent of yield. So working stress or allowable stress are well below yield.

Do you have a link to share on that info?

Thanks,
BB2

 

 

Got any idea if the lug nuts will handle that stress, or will they fail before the studs?

 

Nuts will fail first ,generally, in most instances you will pull the threads out of the nuts before you exceed the yeild on the studs. When studs fail they have usually been exposed to side loading since they are quenched they are surface hardened and any side loading will usually start surface fatigue cracks that will propagate through the stud. You are at much higher risk of wheel bolt/stud failure from under torquing than you will be from over torquing. As soon the wheel stud/nut bolt , starts fretting the dynamic side load on the stud will likely cause it;s eventual failure even if properly torqued later on, once surface cracks start they will propagate with the repeated natural heat cycling induced expansion and contraction of the rim/hub assembly. . This is why many European vehicles use bolts instead of studs as bolts can be more easily examined and replaced.

 

I believe the nuts are designed according to the same working load as the studs with a safety factor as well. My guess is that the nuts will develop the studs to the yield stress at a minimum. Yield stress is not failure of the stud, it is the end of the elastic range where after it takes additional load to take the stud through plastic deformation to ultimate stress which is the peak stress. Some steels continue to failure after ultimate load after additional deformation at a lower load. Some steels reach ultimate load and failure at the same time. This can be seen in a stress strain curve for the various types, grades of steel.

With lug nuts you probably can stress the stud to yield but likely the threads will strip somewhere between yield load and ultimate load. I say this because there has been much written about cautioning against lubing lugs and over torquing them to yield. And I have personally witnessed stripped threads on a lug nut that was abused. If you strip a nut you definitely have damaged the stud as well. Both will need to be replaced. Some failures of studs that I have seen was where the nut was frozen on and the stud was sheared by torsional stress.

BB2

 

I’m 17 and like 130 pounds so I just take my harbor freight breaker bar and use all my body weight until they feel tight lol

 

Couple of thoughts here. Most of the time when I have to buy lug nuts they are some aluminum composite, best I can tell. Feel lighter than plastic. I assume, just based on density that they will yield long before a stud will. Also being lower in the heirarcy of materials, that once cross threaded, only the nut will be damaged. This is all based on having mostly never seen a steel lug nut.

As to rust welded nuts and twisting studs off, wouldn't a little antiseize be better in that case, or at least some sort of oil or grease to inhibit the ingress of water and oxygen?

Furthermore, I believe matthewq4b said under torquing nuts is more likely to damage studs than over torquing. Which to me sounds like the greatest risk to the stud is dry torqing to exact specs and risking a false torque due to rust or a piece of grit which would be compounded by possible rust welding due to previous mentioned ingress of water and oxygen. Also wouldn't you risk damaging the temper of the stud from friction induced heat?

What I'm trying to say is, in my opinion, after reading all of the above, the safest practice is to hand tighten until you're confident the lugs aren't loose, recheck after 50 miles and use a little something to prevent corrosion. Which I think is what >99% of all car owner's have done since the invention of the wheel. I also think those other <1% of all car owner's, ever, is the reason manufacturers have come up with, published, and recommend proper torque specifications - possible at the insistence of their insurance companies. Just a theory....

On a side note, I'm completely willing to allow you to convince me to buy and keep a torque wrench in my truck just for torquing lug nuts. But I don't think it's going to happen.

Sorry to double derail the thread.

 

I can appreciate that lol . You have 5 lugs or 8? I guess your handle is about your truck and not you personally. Otherwise it would be young and fast...I suppose.

 

i have 5 lugs, and yeah my 4 speed granny low transmission with an straight 6 is definitely not that fastest truck around... it will crawl through anything I want it too though

 

To be clear I was talking about steel stock lug nuts. You aftermarket guys are on your own with the alloy wheels and nuts. Follow manufacturer's guidelines there.

I don't keep a torque wrench on board. I have done enough wheels that I trust myself to use a lug wrench. But when I do as soon as I am in the garage the torque wrench comes out. I have several of them. If on the road go to the nearest tire dealer where most offer free torque check. Torque check is recommend every 5000 miles. Change the oil check the torque...

BB2

 

"As to rust welded nuts and twisting studs off, wouldn't a little antiseize be better in that case, or at least some sort of oil or grease to inhibit the ingress of water and oxygen?"

Nope. The stud was broken because the guy was impatient and didn't take the time to use penetrant...he was in a hurry. And it was a seriously abused wheel.

The best practice is clean and dry assembly. Once torqued on apply a tiny amount oil,WD, Fluid Film or what have you to repell water and prevent rust. When changing rims the first thing I do is wash the wheels with soap and water. Let them dry and do the swap. You don't want rust.

BB2

 

I wouldn't say I'm an "after market" guy, just never ended up with steel lug nuts when I've gone to get a replacement that fit. I've seen several vehicles missing one or more studs, sometimes on the same wheel, but I've never owned one. And the only torque wrench I own is I think capped at 80, and that's in inch pounds if I remember right. Now I'm careful when using a large four way make out of a pretty springy steel. Seen lugs snap under them, although being wielded by carefree guys larger in *** than I.
I am curious about your hand tightening, then rushing home to torque. Were they at or above torque when you checked them, or were they quite a bit under?

 

Have you ever had a broken stud? I've never needed to use a penetrating oil on studs/lugs. You in the rust belt?