Like many kids who grew up in the 1980s and 1990s, I am a big fan of public radio programs like "Reading the Rainbow". These programs occasionally delve into the way things are made. During a cool factory tour, the camera becomes my eyes. LaVar Burton is the smarter brother I have never had before. Sites like How Stuff Works are doing a great job of providing similar miracles today, and we try our best to do our part in mountain biking. Some examples are our recent in-depth study of the way tires grip, a large number of articles on off-road construction, carbon fiber rim construction and mountain bike frame design, to name a few.

A few days ago, our editor-in-chief Jeff Barber sent me a research rabbit hole to understand how the brand chooses all the fasteners that hold our bikes and components together. Why is one seat tube clamp 4 mm and the other 6 mm? How many weighting factors are in the decision, and how accurate is the torque recommendation? We emailed several industry professionals to find out.

Based on the responses we received, the choice of bolt head seems to be based mainly on convenience. Brands want to use the cutter heads available on most multifunction tools, with the exception of certain Torx cutter heads because of their higher torque capabilities. In addition, the quincunx head needs to be in a straight line with the bolt head, where a tool can be used to turn the hexagon head at a certain angle to make the hexagon head a better head in a small space.

Cy of Cotic Cycles said: "We usually only try and insist on using well-used 4, 5, 6, 8 Allen wrenches and T25 Torx in specific locations that require access and high torque. There are no major engineering reasons for this, more It’s about what’s best for the customer."

The product engineers at Ibis Cycles agree with Cy. "Whenever possible, we only use cutter heads that can be used with most multifunctional tools. Torx is suitable for high torque applications, but the only size most people have is T25. For most frame pivot hardware, this It’s too small, so we use hexagons everywhere."

Mark Kikkert of PRO delved into some other variables that need to be considered when selecting fasteners. "The choice of bolt tool interface is only part of the equation. In terms of bolt heads, you can also choose shapes such as round, countersunk, flat or hexagonal heads. There are many other types, but these are probably the most commonly used types in the bicycle industry. The factors that play a role in the selection of bolt shape and tool interface are: required bolt strength, bolt size, bolt accessibility and product design.

"For example: Countersunk head bolts are flush with the surface, but usually have a smaller tool interface. If high torque preload is required, then you need to increase all dimensions to get the correct tool engagement. For low preload torque applications, usually Flat head screws or Philips screws or bolts can be used. Hex is a better choice for higher torque levels, and Torx is even better because the tool interface is less likely to slip and wear."

Most bolts on bicycles fit every hole of the same diameter because they have the same thread pitch. For example, the rotor bolts will be installed in the bottle cage mount, most brake and shifter clamps, and several other holes. If you lose a bottle cage bolt on the road, you can borrow one of the twelve disc rotor bolts to prevent it from falling. Before you go home, the rotor should be held tightly with five fasteners. Back in the age of legal weight loss, many XC racers only use three Torx bolts to fix their disks, saving a few grams in total. In any case, how does the brand decide what the pitch of a given component should be?

Although almost everyone says they use standard pitches as much as possible, Kikkert does mention the pollution factor of bicycle bolts.

"For most fasteners, we use standard pitches. Only in special circumstances will the pitch be changed. If fine adjustment is required or the available space is limited, such as a dropper ring, a finer thread may be selected. The finer One disadvantage of the thread is that in a "dirty" environment, the risk of thread jamming is greater, so for these parts, we recommend using anti-seizure compounds. Most visible bolts on bicycle components are almost always regular Pitch."

The component engineer of Rotor Bike Components added the brand's view on fine thread pitch, pointing out that it is suitable for shorter bolts. "If you have two screws of the same metric, the fine-pitch screw has higher tensile strength because it has more contact surfaces, and the fine-pitch screw looses less than the standard-pitch screw. For short screws to withstand For load and vibration applications, fine pitch is your friend."

The frequency of bolt use also affects the pitch of its choice. As the people at Ibis Bikes pointed out, “If the bolts are to be taken in and taken out frequently by the rider, use coarse threads because they are more durable.” Axles and shock absorbers Mounting bolts are two examples. Coarse threads can make the bolts of frequently disassembled parts have a longer service life.

You may have heard stories about professional racers using aluminum or even plastic bolts to reduce weight when possible. How to choose fastener materials for our stock bicycles? Similar to the pitch, it seems to depend on where the fastener is used and the force acting on it. When possible, most companies choose lighter hardware.

Janek Ulatowski from NS Bikes shared their ideas. "We use aluminum bolts or shafts where we are confident that it will not affect the safety or strength of the joint. The only reason is weight loss. Recently, we have started to use extremely durable titanium bolts, which are used in key locations such as shock mounts. The added value is the oil slick finish, which adds extra "golden sparkle" to the whole bike." 

Cy mentions a similar focus, namely the location of the fastener and the load that will be applied to it. "It depends on how much space you have. For example, the seatstay pivots on our Droplink bikes are 8 mm stainless steel because they cannot be larger in diameter within the range of the tubes we use at that location, and they need to be hollow , So that the M5 screw can be screwed into the other end. Due to space and wall thickness constraints, aluminum is not strong enough at all. At the other end of the link, the pivot passes through the seat tube, where there is enough space, so a beautiful 15 mm Aluminum hollow shafts are lighter and harder than steel small shafts."

The standardized strength measurement that sometimes appears on the bolt head is the starting point for Rotor. "There are international standards that define the quality of screws, their resistance to traction and shear, and their materials. The numbers 8.8 and 12.8 that usually appear on the head of screws tell us their quality and resistance. The force that screws must bear will tell you Which screw to choose."

Now we know how to choose fastener materials, but how does the materials being fastened together affect the selection process? For example, I recently studied an aluminum full suspension frame, and when reconnecting the front and rear triangles, I managed to miss the steel washers belonging to the lower pivot. That missing washer caused friction between the alloy and the alloy, and it sounded like the bicycle was eating its own thing.

According to Thomas Westfeldt of Öhlins, it all has to do with the material used to fasten the fasteners. "Usually, the limit is determined by the material of the bolt connection. In our case, it is usually aluminum, and then the strength of the alloy will limit the force."

Ruben Torenbeek from Raaw MTB said his focus is entirely on durability. "Using a small amount of hardware can quickly add weight. Because we focus on durability and functionality, we have more than 700 grams of hardware in one frame." This is a considerable part of the total weight of the frame dedicated to fasteners and bearings . The lightweight carbon fiber XC frame is lighter than the hardware in the Raaw frame, and thankfully, Torenbeek’s bikes are designed to bring very different pleasures.

Certain materials can cause problems when clamped too tightly. Kikkert said: "Stainless steel and titanium bolts rarely have problems. The alloy on the alloy may have a potential risk of wear, so we try to avoid this combination." Two pieces of aluminum rubbing together not only cause damage, but also the frame squeaks. Common cause. Steel washers and fasteners between aluminum parts can solve these problems.

It is only natural that product designers occasionally destroy what they make. Someone must understand how much force things can withstand and what happens when they reach the overload mark. Almost everyone we have spoken to on the subject mentioned the inherent inaccuracy of most torque wrenches. These miscalibrated tools are issues that they must consider in product specifications and design.

At Rotor, there are a few steps before the "Let's Eat" party. "Knowing the force supported by the material and the force that will be applied when using the bicycle (80 kg in the rod screw is different from 2 kg in the water bottle screw), we already have the theoretical value to choose the screw. Then you have to perform real tests and break many To make sure they are correct."

For the steel frame, things are a bit different, although they can still break things on Cotic. "There is a fairly easy to understand torque setting calculation. I use it based on the percentage of nominal preload, elongation, and "elasticity" of the items involved in the joint, but especially when using ready-made steel fasteners. Almost it is. For my own design thread (for example on a pivot), I will calculate the theoretical torque, and then we will break some to make sure the breaking torque is higher."

The people of PRO also calculate first, and then destroy things, and design things as much as possible to let the bolts break first. "Of course, we will break things to find the limits, but initially we designed them to stay together within the expected load limits. Bolts are relatively standardized, and certain sizes, materials, and grades also have a "fixed" maximum load capacity. We try Match the bolt to the intended use. The recommended torque specification is usually that (far) low torque may increase the risk of slippage, while (far) high torque increases the risk of part failure. For example, the handlebar limits you to failure in the rod clamp The strength with which it was tightened before, so we choose bolts that may fail before the handlebar fails to minimize the risk of damaging the most expensive parts of the bicycle. Bolts are easier to replace."

Torenbeek adds a bit of comedy to the extent to which the bolt can be over-twisted. "Very far. The tool interface usually fails first. It needs a very red face."

Regarding the topic of excessive twisting, Cy added that home mechanics need to use some common sense and understand the feeling of fastening fasteners that do not require further rotation. "I kind of hate people blindly sticking to the torque setting when using cheap wrenches. Especially in safety-critical areas such as stems. I have seen the rod move in the rod when someone uses a precise torque setting instead of simply "tightening" it. We are dealing with such small torques on M5 and M6 bolts, and cheap torque wrenches (I mean cheap, I mean less than £200) are usually calibrated so badly that the 5Nm on the rod bolts is more like It’s 4Nm. Now, on larger bolts, the 1Nm difference neither exists nor exists. When I work on the railway, we use a 250Nm wrench to fix things on the train. But on the stem bolts, if That cheap, uncalibrated torque wrench is 1Nm, the torque is less than 20%, so the rod will move, the rider will hurt himself. When customers insist that they use a torque wrench, we have encountered a few times, but it did not Tighten it. We took it back, put our calibrated equipment on top, and found it underneath. The torque is for your safety, but please also use your feel and feel. If the bolt is "correct" on the wrench "Torque" doesn’t feel tight enough, it may not be."

Therefore, some bolts use a finer pitch to prevent them from loosening, while other bolts (such as shafts) are thicker so that they can be removed and reinstalled more easily. When did the brand decide to add thread locking fluid to the fastener to hold it in place? For example, many disc rotor bolts are pre-painted with "Blue 242" and some are missing on the road, if not, I will definitely add some.

For Chris Deverson of Deviate Cycles, the answer is usually yes. "To give you peace of mind, most of our fasteners use medium-sized Loctite. With our sealing system and bearing layout, you should rarely need to disassemble them. So far, we have only sold one set of bearings."

Rotor handles smaller parts than Deviate's people, and their engineers also prefer peace of mind. "Loctite has many types, and they can be used for almost all screws on our bicycles. I recommend using it on screws that are easy to loosen, such as sprockets, saddles or stem screws."

PRO also has a comprehensive thread lock, although it is not a near-permanent variety. Kikkert said: "On bicycles, there is a risk of bolts loosening due to vibration. Therefore, we use and recommend using thread locker on less permanent bolts so that you can loosen them again when needed."

Rotating a bit on this subject, Ibis also wanted to stop the bolts from rattling. Their twist on the threadlock is like this: "The only thing we don't use Loctite is on the bolt that acts as an adjuster. Mountain bikes are subject to constant vibration and complex loads, so almost anything will end up rattling."  

Today, Torx heads seem to have more high-end components. They are, if so, why?

Most people we interviewed said that torx heads are more difficult to reach on bicycles because they need to be connected directly to the bolt heads, while hex heads do not. Cy said: "We try to avoid Torx, mainly because unlike the Allen key, there is no such thing as a ball end Torx. Therefore, you must go directly to the head, which is usually a bit tricky on mountain bikes."

Rotor's engineers believe that the star bolt trend will prevail. "Torx screws allow you to reduce weight and volume, and your wrenches are easier to manage. They will eventually impose themselves on the market."

At Öhlins, they like Torx for several reasons, but prefer to use the bolt heads in the rider's pocket or backpack. "Compared with hex screws and Philips screws, Torx can provide high torque for small screws. It is also not easy to round off. We strive to make our products consistent and rider-friendly by using the tools you carry with you on the road." Although Many multi-function tools have at least one T25 Torx screwdriver for tightening 6-bolt rotors, but they do not yet fully include small star drill bits.

ol' the question of "in a perfect world" should be part of every discussion with product designers and engineers. If there is no user error to worry about, cost is not a factor, and companies can choose fasteners to achieve the perfect strength-to-weight ratio, what would they do differently?

For Öhlins, there is no torque specification in the perfect world. "In a perfect world, the rider does not need to tighten any bolts to a specific torque; the super simple interface will be great to click when properly fixed. A challenge when developing improvements, such as our floating shaft design that ensures minimal friction, is Common ways of doing things that hinder progress. For example, tighten the front axle like the systems used by most of our competitors. If you overtighten it, you may damage the lower part. If you skip the alignment process before tightening the clamp, You won't be able to enjoy the benefits of the front fork." This video shows a visual representation of the axle installation procedure described by Westfeldt.

Rotor's engineers wanted to simplify things even further. "In a perfect world, the bolts will be the same, but people will worry about checking the tightness of the bolts every few thousand kilometers. If the bicycle is used frequently, they will be replaced once a year."

At Cotic Cycles, this transition will be lighter and stronger. "If cost is not a problem, I will always use titanium fasteners instead of steel, because it can reduce weight, but it is difficult to make a value-for-money argument!"

When we jump, all these tests and torque specifications cannot always stay the same. We work hard on mountain bikes and occasionally break or loosen. We make sure to ask everyone for stories about their fasteners causing problems.

Ibis Ibis employees shared stories of excessive use of thread locks on certain frames. "We ran into a problem. I used a drop of Loctite for each bolt to build all the prototypes, but they were well separated. Then we had a production person who thought he did a great job by coating bolt and nut threads thoroughly in Loctite. Well, suddenly people cannot separate their frames without damaging them. Now, our [standard operating procedures] for the frame assembly SOP is more specific."

The problem of tightening different components sometimes appears as the industry changes, and not everyone can get the necessary torque information immediately. On NS bikes, the problem is with the lift seatpost on some models. "With the rapid development of products and technology, we have encountered some problems. It is really hard to avoid. One of them is when the dropper column appears in the industry. Considering our bulletproof off-road vehicles, we tend to over-tighten the seat Pipe clamps, which may cause poor performance. After we discovered the problem, we introduced the [torque] program."

Finally, it is also interesting that the Raaw bike had to slightly increase the torque specifications to meet the force exerted on its sweet gravity frame. Torenbeek said: "We had to increase the torque of the main pivot because we underestimated the clamping force it needs."

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Exciting, ha! I like that the company does consider the tools we already have, although the number of shapes and sizes seems to have increased over the years.

I would rather have plum blossoms everywhere. Considering the cost of mtb components, I think it is also possible to put money into the torx wrench set. Better than having to deal with flaking Allen heads (well, it can also happen to plum blossoms, last time I used a bolt extractor for disc brake screws). In my opinion, the excuse that the screws on the bicycle are not easily accessible... is just an excuse. Just my 2c 🙂

Just thank the industry has not started to use torque to produce bolts! Those can be used safely once, but are garbage after the second use.

How can those guys not know that there is a club driver with a ball head? https://www.kctoolco.com/wera-073599-multicolor-ball-end-torx-security-torx-l-key-clip-set/

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