Originally Posted by
exRunner
I work in an industry that actually torques fasteners that go into space. The requirements for the control, use, and calibration of our torque wrenchs would blow the mind of a backyard mechanic. With that said, torque wrenchs that are affordable to the general public are garbage by that standard. The question is are they good enough to be useful on a bike by a typical end user. The problem with answering that question is there are too many variables.
i personally don't use a torque wrench working on my bikes, and never had a problem. I've seen people snap bolts while using a torque wrench and doing it by hand. I've also been asked to get involved when something came apart after being torqued. Speedplay cleats were the most recent (way too tight because of a damaged wrench). The pattern is a torque wrench won't always save a person who doesn't know what he's doing to start with.
i believe that was the point WhiFi was trying to make.
Aerospace isn't the bike industry was WhyFi's point. So the aerospace standard doesn't apply.
In bold can be explained by simple observation. Ten's of thousands of torque wrenches are used successfully on carbon fiber bicycles at the shop and at home everyday. Count me among them using what you call garbage. You should have been part of the powermeter thread...lol.
If you ever have been around bike mechanics or even within the car industry, you will learn that calibration of wrenchs in many or most shops isn't applied. There is a reason for that. All the bikes they pump out the door assembled with these wrenches of questionable calibration work fine.
So why is that? Are you an engineer? If not, the short answer is, the torque derivation of the specification typically has a safety factor that vastly exceeds the calibration error of most what you call garbage wrenches. That may go over your head if don't have a technical background. Proof? All the bikes that come out of the shops I know where their mechanics use torque wrenches don't crack and they function beautifully. You see, people are adaptive and learn from trial and error. If they break something they learn to not break it in the future. I have never broken a bicycle part using what you call a garbage torque wrench.
A typical seat binder bolt...arguable the most critical juncture on a bike...most are spec'ed in the 55 in-lb range, most won't crack if you torque them to 120 in-lbs. The carbon due to overdesign will take this level of compressive loading. Safety factor is a consideration for how a torque spec is derived.
Point it, the spec doesn't have to be that high. With carbon paste, most 200 lb riders will not have post slippage at 30 in-lbs.