One of the big debates in the mountain bike world, more specifically the DIY mountain bike mechanic world, is whether we need to use a torque wrench when tightening down any nuts and bolts on our most prized possession. Being in the automotive repair industry for over 18 yrs., I know the importance of using them during your final tightening sequence in those applications, but I wanted to find out if it was just as important to torque down the fasteners on my bike as well.
So, should I use a torque wrench to tighten my mt. bike bolts? Yes. If you aim to get the longest life out of your components, minimize stripped and broken bolts or cut down on your repair bill due to human error, then you will benefit greatly from investing in a torque wrench. The worlds best mechanics are using them for a reason, so why shouldn’t you?
Many mechanics, be they auto, bike, motorcycle, or whatever, tend to get a bit of a big head over their ability to turn wrenches, and begin to think they have the ‘magic touch’ for tightening down nuts and bolts going by feel only. And any mechanic worth their salt can tell you just how much of a pain it can be to extract a broken, seized or stripped bolt that was installed incorrectly. Sure, to a 30-year mechanic that has been tightening fasteners most of their life, might have a pretty good hand at guessing if they’ve achieved torque, but without ever using a torque wrench, how would you ever know?
What is the Purpose of Torquing Nuts and Bolts?
Torquing is how we estimating whether we have created enough clamping force on a device to keep it sufficiently attached without overstressing the bolt or component that it is fastening. Due to design difficulties, there currently isn’t a way to accurately measure clamping force in the real world, as it requires an extremely non-cost effective device to do it. So, engineers have done the math for us, and given us torque specs that closely estimate whether we have achieved proper clamping force during reassembly.
This clamping force is what keeps the parts on our bikes from both coming loose, or from slipping and sliding out of place when it’s least convenient. Conversely, when a bolt is over tightened, it can generate either too much clamping force, potentially causing damage to those fancy carbon bars, or even over stretch the bolt, causing it to become weak and brittle.
Imagine a bolt, or stud as a small spring, like the ones in a ballpoint pen. If you grab either end of the spring and pull slightly, it will spring back to its original shape once you release pressure. This is called ‘memory’. Now, if you pull on it a bit harder, you will overstretch the spring, causing it to lose its memory, and not spring back to its original shape. The metal will become hard as well, making it more brittle and easier to break.
The slight give or spring in a bolt actually helps to maintain torque during the heating and cooling of different parts, such as brake rotors and calipers. An overstressed bolt will snap quite easily when subjected to the expansion, contraction and even vibration of each individual part. And this usually happens at the least opportune time.
How to Use a Torque Wrench.
Most torque wrenches today are the click style, which creates a ‘click’ that can be both felt and heard once you have achieved your desired torque. Some have an adjustable range of torque settings, some come preset from the manufacturer. You’ll want to refer to your manufacturer for instructions on how to set it.
- Using a standard wrench or ratchet, progressively and evenly, tightening all the bolts on the component until they are just snug
- Using your torque wrench, begin tightening the bolts a ¼-½ turn each at; alternating or in a criss-cross or star pattern if more than one.
- If one bolt achieves torque much sooner than the rest, loosen it slightly and continue your tightening sequence
- Once every bolt has been torqued to spec, make sure to store your torque wrench properly
What if a Torque Wrench Clicks Without Turning?
During your final tightening sequence, if a bolt doesn’t turn before the torque wrench clicks, the nut or bolt should be loosened slightly then retorqued. Torque wrenches are designed to indicate torque as the bolt is being turned, not when the bolt is stationary. A bolt that is not in motion requires much more effort to get it turning, and may click even if we haven’t achieved torque. Just as easily, the bolt could be overly tight too.
Can I Use a Torque Wrench to Loosen Bolts?
No. Regardless of your instinct here, cause torque wrenches can physically be used to loosen bolts, they shouldn’t be. The amount of force needed to break loose a tightened fastener is much greater than what it was actually torqued too. This excess force can potentially be greater than what the wrench is rated for causing it to lose calibration or even break. Switch to a standard ratchet or closed end wrench for loosening nuts and bolts.
What if the Bolts are Tightened Unevenly?
This can be cause for a bad situation. If a particular component uses multiple bolts to be attached, they should always be tightened down both progressively and evenly. Uneven torque creates an uneven clamping surface, which places too much stress on one side and not enough force on the opposite. Eventually causing breakage, warped rotors or loose parts. Always use a criss-cross or star pattern when tightening two or more fasteners, unless the component manufacturer states otherwise.
How to Store A Torque Wrench
When not in use, a torque wrench should always be reset to its lowest torque setting if possible, and stored either in it’s carrying case (assuming it came with one) or in an area where it won’t get knocked around or have other tools thrown on it in gorilla-like fashion. Torque wrenches are intended to be a precision tool and can be thrown out of calibration by improper handling, or not being returned to their lowest setting before being stored.
Related Questions
Are Torque Wrenches Expensive? A good torque wrench for mountain biking can run somewhere around $45 to $100 on Amazon. There are many different styles, preset, adjustable, some even come as a set with individual sockets and bits.
Do I need to get the best one? No. Though you do want to make sure you get one from a reputable manufacturer that offers some kind of warranty, most for 1 year. There are plenty of good quality torque wrenches out there that can be had for not too terribly much.
Conclusion
If the thought of fubar’ing the carbon seat tube on your shiny new SB130 isn’t enough to convince to use a torque wrench, then maybe this one will. There’s zen to be attained within doing a job well and doing a job right. I walk away from the bike stand every time, knowing that my ride has been reassembled to the VERY BEST of my capabilities. And that in itself brings me peace, both when I’m on the trail, and off.