Originally Posted by
mazdaspeed
Materials technology has come a long was compared to the bikes Sheldon Brown (RIP) had experience working on (he was definitely a vintage guy, in fact I remember him responding to questions I asked on this very forum as a noob). Because of the high modulus and sudden failure mode of composite materials and metals like hardened ti alloys there's a lot less room for error than when you're dealing with steel or big chunks of aluminum. Also stuff like modern crank designs (GXP, campy PT) require fairly high amounts of torque, and can cause failures if they're not tight enough. It's hard to tell unless you have a torque wrench...
Sheldon hasn't been gone so long that he didn't work on carbon and Ti quite regularly. He was a full-time mechanic in a busy shop who had to be up-to-date on technology.
The editorial update on torque settings since Sheldon's passing expands on this:
"[I find this generally to be true, but many bicycle components now are accompanied with spec sheets with lists of torque settings. There are two reasons for this:
Consultants to attorneys measure torque values, leading to an excess of caution by the manufacturers
Some components made of unusual materials (carbon fiber seatposts, aluminum bolts) require lower torque settings than for other parts of the same general type.
This paragraph added by John Allen] "
I'm guessing by your user name that you come to cycling from an automotive background where the use of torque wrenches is often very important, but it's a misapplication of that experience to assume that the same is true for bicycles. I spent the better part of a decade repairing light industrial machinery where the applications for torque wrenches were rare but important in those very few instances. Bicycles just aren't cars or injection molding machines.