Threaded #55: Things to know when using a torque wrench

Dave Rome

A tool is only as good as its user. It’s a clichéd saying, but one worth repeating when it comes to correctly using a torque wrench.

Many who work on bikes believe that the click of a torque wrench is the sign of safe wrenching. However, there are nuanced and overlooked details that anyone wielding such a tool should be aware of. This article summarises the most commonly missed of those details.

I wrote a similar article before Escape Collective was conceived, and I continue to want to share those words with curious readers on a near-weekly basis. So here we are. As always, there’s nuance in any technical topic, and some of the lessons here will only apply to certain situations and types of torque wrenches. I’ll try to make that clear as we go.

To coincide with this edition of Threaded, I sat down with Escape Collective member Alex Boone to record a geeky bonus podcast episode. Boone, once a bike shop rat, now works at the NASA Jet Propulsion Laboratory and was formerly a quality engineer at Motiv Space Systems. In other words, his knowledge in using a torque wrench is out of this world (sorry – even I cringed while writing that).

Wet vs dry fasteners

Fastener torque is a tricky subject. For a deeper understanding, you could read _NASA’s Fastener Design Manual_or a copy of Machinery’s Handbook. Or you could just understand that for the purpose of bicycle mechanics, the recommended torque values are based on measuring the fastener friction, with the goal for it to achieve the desired clamping force across a bolted joint interface.

For a torque wrench to accurately apply the intended clamp load there are some assumptions made regarding the condition of the thread and how it is prepared. "The difference between a dry and lubricated fastener will affect the amount of clamping load you can apply to that fastener for a given torque," explained Boone. "A lubricated fastener allows you to apply more clamping force for the same twisting force."

Grease, anti-seize, thread locker, or just dry? It can make a big difference.

“When the fastener is dry, you have unknown and often variable friction between the thread surfaces, and are also much more likely to experience high and/or inconsistent forces or binding under the bolt head," Josh Poertner of Silca previously shared on the topic.

This quickly descends into a deep rabbit hole regarding thread preparation, quality of fasteners, material, diameter and shaping of fastener heads, alignment, coatings, types of lubrication used, and even how the lubrication is applied. I’m not going to get into the weeds about how using anti-seize will produce more clamp force for a given torque than standard grease (it does), rather, I’ll just say to follow the manufacturer's instructions whenever provided.

An increasing number of component and bicycle manufacturers will outline what to apply to a thread or when to keep an interface dry (clean and not lubricated). If in doubt, apply a small amount of grease to the thread, or consider using a thread locker if there is concern it may loosen due to insufficient torque or excessive vibration (such as around brakes).

Regarding thread lockers, running torque is common in bicycle wrenching. “Running torque is basically just friction between the fastener and the thread interface," said Boone. “Anyone who has installed a six-bolt rotor onto a wheel will have experienced running torque from the big blob of blue Loctite that prevents you from freely screwing in the M5 fastener. That force that you're feeling as resistance is a form of running torque.”

SRAM lever clamp bolts have proven to be a component impacted by running torque.

Often, that increased running torque isn’t a concern, but occasionally it can present problems, such as with the tightening of SRAM’s dropbar levers where excess running torque resulted in component slippage and a subsequent recall. “For practical purposes, it makes more sense to just clean the threads, maybe put some fresh liquid Loctite on there, and then just do it up to whatever the factory specification is,” said Boone – advice for when you’re experiencing excessive running torque from a dry patch thread locker.

Threaded is an ongoing series created for professional mechanics and enthusiast home mechanics in search of continuous improvement, or at least ways to bring more efficiency, precision, or joy to the work.

It’s photographed, written, and created exclusively by me, Dave Rome. With approximately 20 years of experience on the tools, and more than a decade of documenting other mechanics' work, I aim to share my passion for finding quality tools and tips on how best to use them.

This series takes many hours to create, and the information shared often isn't available elsewhere. It's merely through the support of our members (readers) that this content exists.

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Safe storage, safe use

Torque wrenches are precision instruments and should be treated as such. However you'd treat a football, do the opposite with your torque wrench: don’t throw it around, take care with how it's stored, keep it away from children, and avoid excessive humidity.

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