Lets discuss the science of torque specs

[blown motor]

I have to replace the brakes on my daughter-in-law's 2013 Mazda 5. So I pulled up a YouTube video just to check that there's nothing weird about it. When replacing the caliper mounting bracket it says to torque to 40 ft/lbs. That got me thinking about the science behind torque specs. Years ago, before I had a torque wrench, I just TIGHTENED things. So what if I tightened these bracket bolts to 60? What would it matter? I get it that if there's a gasket involved that the wrong torque could effect the performance of the gasket. Or, on wheels, that if you hit a pothole, let's say, and the rim flexes that it'll put an extreme load on a couple studs. A stud that is overtightened risks being broken in that situation. But for most things, what does it matter if 10 or 20 or 30 percent one way or the other, aside from not being tight enough to stay tight.

Just curious about the science.

[dodj]

How smart do you think we are?!?

[EDL94]

Just tighten it till it loosens. 

[jimynick]

"just tightened things" We used to say make it (in a Germanic slur) "nizen tight, guten schnug". Steel on steel it's the torque capacity of the fastener IMO. Being an "experienced, not old farmer" you've likely tightened more fasteners than most guys have had hot dinners and I'll bet damn few ever came off. Aluminum is a whole different deal though and I own three torque wrenches accordingly. Just twist 'er till it snaps and give 'er another quarter turn, eh?

[Jay Bee]

That's a deep question, like....

[blown motor]

How smart do you think we are?!?

 

[blown motor]

Steel on steel it's the torque capacity of the fastener IMO.

That's what the way I look at it too. That's why I like to stop an eighth turn before I snap it off. Misjudged that one the odd time. 

[Brads70]

I thought these were a measurement? Like tighten to 30 fig newtons ?  That or tighten it as tight as you can, then one more turn? 

  

[BIGSHCLUNK]

If I had an accurate way to calculate...     Lets just say I'm sure when it's all said an done I've torqued less than 1% to "specs" in the last 55 years maybe longer. I cant forget all the bicycles     

[Mr Lee]

My good friend works in a garage and does brake jobs all day long.  I've never seen him pull a torque wrench out for brakes.  Tightening head bolts on the other hand... different story I guess but... 

So, to answer your question, I would say.... good question.  haha

Typically, the bigger the nut, the more tightness it needs and can withstand.  However, the nut that holds the wheel bearings in is large but that gets minimal torque.  So.... 

Yeah, nothing conclusive to see here.    You've got to break a few bolts to learn how tight, too-tight, is. 

[tparker]

Yeah I always just "tighten" things. Never had  too many problems. I have snapped a few bolts here and there, but I have spent many hour cursing some OTHER bastared that overtightened something  (Spark plugs or oil filter usually).  LOL. I just finished rebuilding a Jeep 4.0 and I used the torque wrench all through out. Honestly, I think a little common sense can get you in the ball park for most things. I think in most cases the torq spec just keeps you at some optimal value so it isn't too loose that  the bolt comes loose or too tight that you stress the bolt. But I would think it is more critical for heads, exhaust manifolds and a few other items.