Torque Education Needed

[Oka]

Hello folks, I would need some clarification on the science/physics of torque specifications.

A. 2006 Toyota Sienna, AWD has a lug nut torque of 75 ft.lbs

B. 2001 Volvo XC70 owner's manual specifies 100 ft.lbs for lug nut.
On line specifies 105 ft.lbs, which is 5 ft.lbs more than the OEM manual.
1. Logically, 5 ft.lbs is not much of a big deal, right?
2. Why would a 2001 Volvo XC70 have a higher torque than a 2006 Toyota Sienna?

C. 2001 Volvo XC70 Vibration Damper (4 screws)
Stage 1 = 18.5 ft.lbs
Stage 2 = 30 Degrees
3. First stage means to torque to that set amount, then turn 30 Degrees.
4. If so in (#2), why isn't the "30 Degrees" calculated and included to the Stage 1 torque. In such case, there would be only one torque to say, example, instead of the specified "Stage 1 18.5 ft.lbs" it would be just one 20 ft.lbs torque?

Thanks, for I am still work in progress!

[Brett San Diego]

I'm not an engineer, but I can share a couple of comments.

A major factor in torque specs is the hardware involved. The lug bolts on the XC70 are M14. I'm guessing the Sienna has M12 studs or bolts. Smaller bolts, lower torque spec.

The actual clamping force generated by tightening a bolt with a torque wrench (which depends on how far the bolt turns) is dependent on the friction present when tightening that bolt. There's the possibility of variability in the actual clamping force when relying entirely on the torque on the wrench because friction may vary from bolt to bolt. Maybe one has some roughness/corrosion on the threads causing high friction. It won't get tightened as much at the same torque setting on the wrench. Tightening to a certain angle measurement is more accurate in terms of generating consistent clamping force across multiple bolts holding a part in place because each bolt is turned the same amount. Bolts that are specified to be tightened to an angle measurement are also special bolts. They're "stretch bolts" designed to stretch upon tightening so that the bolt reaches the appropriate clamping force without going over. That's why they should be replaced after one use. Once they've been stretched, they should be replaced.

Brett

[Oka]

I'm not an engineer, but I can share a couple of comments.
. . . . . Bolts that are specified to be tightened to an angle measurement are also special bolts. They're "stretch bolts" designed to stretch upon tightening so that the bolt reaches the appropriate clamping force without going over. That's why they should be replaced after one use. Once they've been stretched, they should be replaced.

Brett

Interesting to know. I had wondered why some bolts have 'degree torque', as extra, and some don't.
Thank you for the knowledge.

Cheers

[Astro14]

I see that Brett already explained it, but since I hadn’t read this post yet, I answered your other post.

Cheers!