Quote:
Originally Posted by extrashaky
Jeez, how did I miss this thread?
I have to pile on here. You can overtorque them, which can stretch the studs, which then makes it difficult to get them tightened again, which leads to additional overtightening, which eventually causes failure. It's not like you have to carry a torque wrench in the car with you, but it's really a basic part of the tool kit that ought to be in the garage. I have replacement axles for my Jeep, and one of them has some stretched lugs on it that I'll have to replace before I'll feel comfortable using it, the result of someone getting overzealous with a wrench.
Furthermore, overtightening can make it a bitch to get the nuts off some cars. I had to have mine extracted off my Jeep by a tire shop because the idiot who put the last tires on overtightened them, and the two-piece lug nuts came apart when I tried to change a tire.
I replaced them all with spline drive and made sure they were torqued correctly. I liked them so much I put spline drive nuts on my BRZ as well.
A good tire shop will use torque adjustable impact wrenches that are regulated so they don't overtorque, and they'll dial in the appropriate torque for the hub they're working on. Unfortunately there are a lot of mediocre tire shops that don't bother.
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Quote:
Originally Posted by extrashaky
I'm not sure that's true. When I torque mine to 89 ft lbs with my torque wrench, I'm certainly not at the limit of my strength, and I'm not all that strong. I was actually pretty surprised how little effort it took to get them to the proper torque. I couldn't snap a stud the first time the rims were pulled off, but if I were swapping tires frequently I could likely do some cumulative damage. As has been noted, people do have issues with overtightening.
Furthermore, not everyone uses a "proper lug wrench." A few people in this thread have talked about using impact wrenches. Some of them may have been lucky because they weren't using a wrench with a lot of power. Additionally, if you use a breaker bar to get the lugs off (I usually do), it's quite tempting to use it to tighten them also if someone on the internet told you that you can't overtighten a lug nut and you believed it.
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Well, you presented a good fair number of pretty shaky assertions there. One could even0 call them... Extra shaky.
Jokes aside, there is a tremendous amount of misinformation in your posts.
First, yes, any bolt can be overtorqued enough to stretch it.
Second, torque settings alone are an incredibly inaccurate way to ensure correct fastener preload. That is a fact, we can argue the engineering details if you like.
Third, most impact wrenches are adjustable, but
none of them, not even one, delivers consistent performance. This is by the nature of delivery. The short duration pulses transfer energy in a discontinuous fashion, the final clamp load is influenced heavily by the frictional coefficients of both the threads and the surface which bears the clamp loads. It is also affected by the spring coefficients of the joint material, the heat generated during tightening, and the motion of the gun. This can be demonstrably proven.
Fourth, even with a powerful impact gun, you are unlikely to even damage a lug, much less break it.
Fifth, all steel fasteners stretch when loads are applied. This is called elastic deformation, and it's what gives the bolted joint it's tensile load. For all intents and purposes, elastic deformation in steel can be repeated an infinite number of times without causing fatigue or failure. In other words, no, they can be "overtorqued" an infinite number of times without causing "cumulative damage."
If they are stretched beyond the
yield point, they will undergo plastic deformation, which is irreversible and causes damage, usually visible. These are your "stretched lugs." That is "cumulative damage." But in order to do that to a normal, undamaged wheel stud, you have to have an extra bigass breaker bar or you need to join the avengers.
Did you know, for example that if you torque a fastener, then remove, clean, and lubricate it, and apply the same torque again, you will
almost double the tensile load applied to that very same fastener? Yes, that $40 Sears click-wrench is a proper precision instrument, you know. *sigh* A $300 digital torque wrench is subject to the same problems and limitations.
For that matter, I have replaced hundreds of wheels with impact wrenches. Never lost one. Never had anybody else lose one.
Now what's
really funny is watching people replace components with different and dissimilar ones, sometimes made of
different materials than the factory components, and then faithfully copy the torque specs right out of the manual.
Now that is UN-F*CKING-SAFE For reasons I can demonstrably prove over and over and over.