The service manual for my vehicle specifies torque for most nuts and bolts in ranges. Are there any reasons to be at the lower or higher end of the range, or somewhere in between?
Different expected driving conditions, warmer or cooler climate, anything like that?
No, I think it has more to do with an expected range, given the vast number of torque tools, operator technique, and the distinct lack of calibration of most folks' torque wrenches.
(And I am as or more guilty than most... my elbow used to click +/- 2 lb-ft. Now, after four decades of wrenching on things, my elbow clicks just attempting to get out of bed and strap on my various trusses...)
Unless you want to send your torque wrench out for calibration (and who does that??) set it to the midrange of your manual specification and be happy! Keep in mind that most folks don't even read the manual, so you are already way ahead on this endeavor.
The minimum is the minimum, the maximum is the maximum, but in truth most automotive applications are based on female threads that are far weaker than any true fastener rating. Set to the midpoint, torque, be happy, you're all good.
ON EDIT:
Hey, I am all for regular torque wrench calibrations; please don't misinterpret my harsh old coot ways. BUT, it's not always easily accessible and/or affordable for the Regular Joe DIY guy, of which I am not.
I have spent almost as much on SnapOn as I have on alimony, and I assure you the former is a better value. When you are putting back together suspension parts, you need to have a good feel. Not much more. "GoodNtite" works here. When you are final torquing an aluminum head down on a high performance engine, you may need special lubricants, instructions, angle torque, and a lot of experience. And most of all, a really nice and calibrated top-tier torque wrench.
Bottom line is this: If you care, you'll be fine. Torque specs are quite sloppy on anything except Rocket Surgury and head bolts, and the latter comes with great instructions and often bespoke thread lubricant.
I buy some things from Harbor Freight, but I'm embarrased to admit that. If you really want to wrench stuff seriously, invest in a good Snapon/MAC/Matco torque wrench (I suggest 1/2" drive) and enjoy it (with occasional calibration) for the rest of your life.
Unless aligning for a locking mechanism, cotter or split pin with a castellated nut, it is common practice to go mid range.
If aligning for a split pin, first torque to lower limit and check hole alignment. If aligned - bingo. If not, set upper limit and incrementally rotate not to achieve hole alignment whilst not exceeding upper limit.
If you get to the upper limit and still not hole alignment then consider adding or removing a washer, or using a thin washer.
Assuming you are applying torque to the nut. If you are applying torque to the bolt head then go to the upper limit as some torque is absorbed by the friction of turning the bolt on the hole.
Torque is an indirect way to measure bolt tightness and not a real accurate way to measure it.. Torque can vary a lot depending on the condition and lubrication of the threads. For more precise applications like aerospace, they specify bolt stretch. The way a bolt works is by stretching like a very stuff spring, The clamping force the bolt exerts is proportional to it's diameter and the amount of stretch.
