He didn't mention which one it was, but I bet a 1" impact is probably well over 1000 foot pounds, probably in the 1500-2000 found pound range. Here's an air one that claims 2070 foot pounds.
Dealer Severely Overtightened Lugnuts!
- Thread starter SwampSurvivor
- Start date
"Tightened to" is irrelevant to removal specs. Thread pitch and cleanliness of the fasteners have a lot to do with it as well. Why do people have so much trouble removing Honda crankshaft pulley bolts with a 1/2 inch impact? It's torqued to well under 400 lb-ft.
If you cringe when seeing someone use a torque wrench to remove a bolt.
Don't forget fit class
That's somewhere between difficult to impossible to address directly without more information.
Assuming a properly selected joint with dimensional mechanical integrity......
The additional considerations are the tension required to exert proper clamping force on the joint proper.
That has to be considered then against the fatigue strength of the fasteners ( lug and nut combination)
So, in your scenario, lets say that 160lb-ft is well within the capability of the fastener but the load and hardness of the fastener adversely compresses or otherwise changes the dimension/geometry of the joint parts ( distorts the rim hole) causing loss of tension at the rated torque but could be advanced further and regain it.
In that scenario- there is no danger of fatiguing the fastener but rather damaging the joint mechanics.
Turn it upside down-the rim is stronger than the fastener group- then depending on where that 160 lb-ft sits in relation to the tensile strength of the fastener then you will probably initiate progressive fatigue at an undefined rate.
Just remember this
Initial tensioning (torqueing) is a single static value based on rotational forces indirectly assessed against a number that means nothing to begin with.
After that and the joint is loaded- many other variables come into play such as additional loading, distortion, corrosion, surface finish, galling, particles and many others which "add' to the initial tensioning resulting in a fastener that is resisting turning more than the load it is holding.
In other words, it may not just be the effect of the torque wrench that's making it so tight. ( emphasis on the may not)
Co-incidentally the is another thread going on torque sticks. They would be helpful as long as they were being used correctly.
In truth, the impact has a different set of physics than the pull handle.
A high frequency high amplitude series of shocks not giving the corresponding material time to conform to the stresses and release is different than a continuous load leading to an apex where the COF is finally exceeded and displacement begins. ( you actually have more resistance and heat build up grabbing even more with this method)
Assuming you have a clean lug nut and everything with no rust, dirt or corrosion and have an accurate and calibrated dual direction torque wrench.
If you properly torque a lug nut to 80 lb-ft and change direction to loosen the lug nut, what can you expect?
Basically:
- lug nut torqued to 80 lb-ft.
- We allow +/- 5% to loosen
Can we consistently expect the torque setting of 76 lb-ft to click and 84 lb-ft to loosen the lug nut?
gathermewool
Site Donor 2023
Where are you getting this 5% from? I would imagine the static coefficient of friction (COF) for this type of fastener to be much higher. Remember, the lug nut and wheel surface are usually far from perfect surfaces, which add to the static COF.
Another factor is when the torque wrench clicks, if using that kind of wrench to tighten. I ALWAYS try to get it to click WHILE the wrench is rotating, but have sometimes had to back off when I run out of room. Since I’ve stopped I’ve then transitioned from dynamic to static COF. I might find that the wrench will click right away as i begin to rotate without any additional movement of the lug nut. So, in this case, the lug nut is torqued to a lower value than if I was able to continually rotate the wrench until it clicked.
Many things affect breakaway torque, so I would guess it’s impossible to guess breakaway torque, except with empirical data from same setup eg, same wheels and lug nuts or similar.
Unfortunately no ( obviously meaning literally there is no set percentage of "breakaway" torque[BT] and no way to know all the contributing effects of said torque)
For the purpose of this- we are going to null all other things like deformed threads, corrosion over time, effects of thermal loading, weathering and so forth)
Let me explain why and try to un muddy the water on a very dull subject.
"torque" is a twisting force that "stretches" ( elastic) material ( both the joint materials and fastener) to form a preload on the joint.
That's part 1 and to know what that contributes to the additional BT requirement you will have to know the loading of all those elements.
Part 2 is all other forces on the joint (the working load)- over time these forces cause that tension to set (fatigue) and even deform surfaces (changing geometry) and even "work harden" them.
Those are "mechanical" additional variables way outside any joint torque that will have to be overcome to loosen the joint.
Pretty much impossible to capture and calculate because of the randomness of occurrence and individual extent. ( sometimes nothing happens and they will torque off at the same as application- other times they lose all tension and walk off)
That's why its really impossible to estimate any breakaway torque requirement with any degree of legitimate repeatable accuracy.
With all these variables involved , can we pick a reverse torque number that overcomes all these issues?
For example we torque a lug nut to 80 lb-ft.
Can we expect to loosen at 96 (80 + %20) or 112 (80 + %40).
Is there a number (80 + %50?) that for sure can overcome all these other factors?
Trying to figure out what part of Op's issues was due to this.
For example we torque a lug nut to 80 lb-ft.
Can we expect to loosen at 96 (80 + %20) or 112 (80 + %40).
Is there a number (80 + %50?) that for sure can overcome all these other factors?
Trying to figure out what part of Op's issues was due to this.
He is my absolute favorite! I never thought I could "miss" a celebrity, but I certainly miss him!
I can see needing a VIN for lugnuts on a Ford. There's multiple thread pitches available for my 2001 F350 4x4 SRW truck. I only know that because I bought wheel bearings with the wrong thread pitch.
Pick one? sure but I don't know that I could defend it professionally if challenged but if we assumed a properly engineered joint tensioned properly with no advancement of corrosion or other weathering, I could "reasonably" promote about a 15-20% amplitude of BT to start the loosening process. (I go that high because theres still that work loading monster prowling out there in the tree line just out of view.... but you can hear the breathing)
oilUzzer- we're talking dynamic COF vs. static. As you tighten the bolt, it is rotating (dynamic) the whole time until it reaches the selected torque and the wrench clicks over. The bolt is now at 80ft-lbs. To loosen requires about 20% more as it is now static friction to overcome which is always higher than dynamic (all things staying the same). Imagine moving a large heavy box, initially at rest (static) on the floor. To get it moving requires alot more force, but once it begins to move, alot less to keep it moving. This is static vs. .dynamic . The bolt in your case is at 80 ft/lbs but requires that and an additional 20% or 96ft/lbs to initially loosen
Not only that, but crank it down a few hundred pounds and then don't touch it for a few months so rust can set in and it will take a lot more than the initial amount of torque that was used to put it on.
Similar threads
