Like a lot of kids growing up in the 1980s and 90s, I was a huge fan of community radio shows like Reading Rainbow, which got into how things were made from time to time and let the camera be mine on the cool Eye factory tours. . LaVar Burton is the smartest big brother I’ve ever had. Today, sites like How Stuff Works are great at handling surprises like this, and we do our part when it comes to mountain biking. For example, we recently published detailed articles on tire grip, extensive articles on off-road construction, carbon fiber rim construction, and MTB frame construction, just to name a few.
Our editor-in-chief Jeff Barber sent me down the rabbit hole the other day to find out how brands choose all the fasteners that hold our bikes and components together. Why is the head of one seatpost clamp 4mm and the other 6mm? How much do the weights affect the decision and how accurate are the torque recommendations? We emailed several industry professionals to find out.
Judging by the answers we received, the choice of bolt head is based primarily on convenience. Brands want to use the bits available in most multi-tools, with the exception of some Torx bits, which are chosen for their higher torque. Also, the Torx head needs to be in line with the bolt head, the hex head can be angled with a tool, making the hex head the best head in tight spaces.
Sai of Cotic Cycles says, “Usually we try to use a good 4, 5, 6, 8 and T25 hex wrench only in certain places where we need access and high torque. There is no major engineering reason for this, anymore. the best for the client.”
The product engineer at Ibis Cycles supported Sai’s opinion. “Whenever possible, we only use bits that are suitable for most multitools. Torx is great for high torque applications, but the only size most people have is T25. everywhere.”
Mark Kickert from PRO analyzes some other parameters to consider when choosing fasteners. “The choice of bolt tool interface is only part of the equation. As for the bolt head, there is also a choice of shapes such as round, countersunk, flat, or hex. There are many other types, but this is probably the most commonly used in the bicycle industry. Factors, that play a role in choosing the bolt shape and tool interface are the following: desired bolt strength, bolt size, bolt availability, and product design.
”Example: Countersunk bolts are flush with the surface, but generally have little tool contact. If high torque preload is required, you will need to oversize everything to ensure proper tool engagement. For low preload For applications torque loaded screws or bolts can usually be used with a flat head or Phillips head. Hex is better for higher torque levels and Torx is better because there is less chance of slippage and wear on the tool interface.”
Most bolts on a bike fit all holes of the same diameter because they have the same thread pitch. For example, rotor bolts fit bottle cage mounts, most brake and derailleur clamps, and a few other holes. If you lose a bottle cage bolt on your track, you can borrow one of the twelve disc rotor bolts to keep it from falling out. The rotor must remain on the five clasps until you return home. Back in the days of legitimate lightweight, many XC riders simply used three Torx bolts to mount their rims, saving a modest gram in the process. In any case, how do brands decide what the thread pitch should be for a given component?
While just about everyone says they use standard pitches whenever possible, Kikkert points to the contamination factor of bike bolts.
”For most fasteners, we use a standard thread pitch. Only in special cases, the pitch can be changed. If fine tuning is required or if space is limited (for example, dropper pin rings), thinner threads can be selected. Thinner threads have the disadvantage that that in ‘dirty’ conditions there is a greater risk of thread sticking, so we recommend an anti-seize compound for these parts. Most visible bolts on bicycle parts have a fairly normal pitch.”
A component engineer at Rotor Bike Components added to the brand’s view of the finer pitch by saying it works with shorter bolts. “If you have two screws of the same size, a fine pitch screw has a higher tensile strength because it has more contact surfaces, and a fine pitch screw will loosen less than a standard pitch screw. and vibrations, a small step is your friend.
How often the bolt is used also affects pitch selection, as Ibis Bikes notes: “If the rider will be putting the bolt in and out frequently, use a coarser thread as it is more durable.” two shock absorber mounting bolts. For example, coarse threads provide longer bolt life for frequently dismantled components.
You’ve probably heard stories of professional racers using aluminum or even plastic bolts whenever possible to save weight. How to choose the mounting material for our production bikes? Like thread pitch, it appears to depend on where the fastener is used and the forces acting on it. Most companies opt for lighter equipment whenever possible.
Janek Ulatowski of NS Bikes shares their philosophy. “We use aluminum bolts or rods when we know we won’t compromise the security or strength of the connection. The only reason is weight savings. Recently, we’ve started using extremely strong titanium bolts, which are used in critical places such as impacts. Their added benefit is is a smooth surface that gives an extra “shine” to the entire bike.
Cy mentioned similar concerns about the location of fasteners and the loads that would be placed on them. “Depends on how much space you have. For example, the seat stay hinges on our Droplink bikes are 8mm thick stainless steel because they can’t be larger in diameter within the tubes we use at this location and they need to be hollow. Thus, the M5 screw can be screwed into the other end. Aluminum is not strong enough due to space and wall thickness limitations. At the other end of that link, the pivot goes through the seat tube and there’s plenty of room, so a nice big 15mm aluminum hollow axle is lighter and stiffer than the smaller steel axles.”
The standard strength measurement that sometimes appears on the bolt head is the starting point for the Rotor. “There are international standards that define the quality of a screw, its resistance to traction and shear forces, and the material. The numbers 8.8 and 12.8, which usually appear on the screw head, tell us about their quality and strength. The amount of force applied by the screw Must withstand will tell you which screw to choose.
Now we understand how to choose a fastener material, but how does the fastener material affect the selection process? For example, I was recently working on a full-suspension aluminum frame, and when reconnecting the front and rear triangles, I was able to skip the steel washers related to the lower pivot. That missing washer was causing alloy to alloy rubbing, and it sounded like the bike was eating itself.
According to Öhlins’ Thomas Westfeldt, it all depends on the material to which the clasp is attached. “Typically, the limit is determined by the material the bolt is attached to. In our case, this is usually aluminum, and then the strength of the alloy will limit the force.”
Raaw MTB’s Ruben Torenbeck says he’s completely focused on durability. “We can add weight quickly with a small amount of equipment. Because we focus on durability and functionality, we have over 700 grams of equipment in a single frame.” That’s a decent portion of the overall frame weight, dedicated to fasteners and bearings. The lightweight carbon fiber XC frame weighs only slightly more than the Raaw-framed hardware, thankfully Torenbeek bikes are built for a whole different kind of fun.
Some materials may cause problems if clamped too tightly. “Stainless steel and titanium bolts rarely cause any problems,” Kickert said. “Alloy on alloy is a potential galling risk, so we try to avoid that combination.” Common sources of creaking. Steel washers and fasteners between aluminum components can solve these problems.
It goes without saying that product designers sometimes break what they are doing. Someone needs to see how much force things can withstand and what happens when they reach the overload mark. Almost everyone we talked to about this topic mentioned the inherent inaccuracy of most torque wrenches. It is these miscalibrated instruments that they must take into account in product specification and design.
In Rotor, there are still a few steps before the Let’s Eat party. “Knowing how much force the material can withstand, and how much force you are going to apply when using a bike (80kg rod is not the same as a 2kg water bottle screw), we have a theoretical value to choose a screw for Then you need to do a real test and check many more. Make sure they are correct.”
With steel frames, things are a little different, although they still break something on the Cotic. “There is a fairly easy to understand torque setting calculation that I use based on the percentage of nominal preload, elongation, “elasticity” of the elements involved in the connection, but especially when using standard steel fasteners. For threads of my own design (for example, on a hinge), I calculated the theoretical torque, and then we broke off the part to make sure that the torque was higher.
The PRO guys also count first and then break things, designing things so that the bolts break first as much as possible. “Of course we take things apart to figure out the limits, but initially we designed them to be held together within expected load limits. Bolts are relatively standardized, and certain sizes, materials, and grades also have a “fixed” maximum load capacity. We tried to match the bolts to the intended use. Recommended torque values are usually such that (much less) torque can increase the risk of slippage, and (high) high torque can increase the risk of failure of the part. For example, the steering wheel is limited in its capabilities. How difficult it is to tighten the handlebar clamps before they fail, so we choose bolts that are more likely to fail before the handlebar fails, minimizing the risk of damage to the bike’s most expensive component. Bolts are easier to replace.”
Torenbeck adds a bit of humor to the question of how tight a bolt can be. “Very far. Usually the first thing to go wrong is the interface of the tool, which turns very red.”
Speaking of overtightening, Sai added that home mechanics should use common sense and understand what it’s like to not have to tighten any more fasteners. “I hate it a little when people blindly stick to torque settings when using cheap wrenches. Especially in safety-critical areas such as stems. Dealing with such small torques on M5 and M6 bolts and cheap torque wrenches (by cheap I mean under £200) are often so badly calibrated that 5Nm on that bolt is more like 4Nm. Now, on the big ones bolts, 1Nm difference neither there nor there When I worked on the railroad, we used 250Nm wrenches to screw things to trains. will move and the driver will be injured. We have had several cases where customers insisted that they used a torque wrench, but it would not tighten. We take it back, put a calibrated gear on it, and find it down there. your safety, but use your feeling and feeling. If the bolt feels under the “correct torque” on the wrench. If it’s not tight enough, it probably isn’t.”
Thus, some bolts are finer pitched to prevent loosening, while others (such as shafts) are thicker for easier removal and more frequent reinstallation. At what point did brands decide to add threadlocker to their fasteners to keep them in place? For example, many of the disc rotor bolts come pre-coated “242 blue”, some were lost along the way and if not I’d be sure to add some.
For Chris Deverson of Deviate Cycles, the answer is often. “For your peace of mind, we use medium size Loctite for most of our fasteners. Thanks to our sealing system and bearing arrangement, you rarely need to remove them. We have only sold one set of bearings so far.”
Rotor handles finer details than the folks at Deviate, and their engineers also prefer a laid back approach. “There are different types of Loctite and it can be used for almost all screws on our bikes. I recommend using it for those that tend to come loose, such as chainrings, seat or stem screws.”
The PRO also has thread locking across the board, but not a near-permanent variety. Kickert says: “On a bike, there is a risk of loose bolts due to vibration. Therefore, we use and recommend using a threadlocker on weaker bolts so that you can always loosen them again when you need it.”
A little twist on this, Ibis also wants to make sure the bolts don’t come loose. Their turn on the threaded lock looks like this: “The only place where we do not use Loctite is in the adjusting bolts. Mountain bikes are subject to constant vibration and complex loads, which is why almost everything eventually starts to rattle.”
It seems that more and more high quality components are equipped with Torx sockets these days. Do they exist, and if so, why?
Most of the people we spoke to said that Torx heads are hard to get on a bike because they require a direct connection to the bolt head, which is not required for hex sockets. “We try to avoid Torx as much as possible, mainly because, unlike a hex wrench, there is no such thing as a ball head Torx. So you have to go straight into the head, which is usually a bit tricky on mountain bikes. . “says Sai.
Rotor engineers believe the star bolt trend will prevail. “Torx screws reduce weight and bulk and make your wrench easier to handle. Finally, they will declare themselves on the market.”
At Öhlins, they prefer Torx for several reasons, but prefer to use bolt heads in the driver’s pocket or backpack. “Compared to hex and Phillips screwdrivers, Torx can provide high torque for small screws. It is also less prone to rounding. We strive to make our products stable and driver-friendly using the tools you use on the road.” Although many functional tools have at least one T25 Torx screwdriver for tightening 6-bolt rotors, not all of them include a small sprocket.
The age-old question “in an ideal world” should be part of every discussion with product designers and engineers. If the user didn’t have to worry about error, cost wouldn’t matter, and companies could choose fasteners to achieve the perfect strength-to-weight ratio, what would they do differently?
For Öhlins, in an ideal world, there are no torque specifications. “In an ideal world, a rider wouldn’t need to tighten any bolts to a certain amount of torque; a very simple interface with a click when pinned properly would be great. The challenge when designing improvements like ours is to keep friction as low as possible. Floating axle design is a common way to do things that get in the way of progress. For example, tightening the front axle, like the system used by most of our competitors. If you over tighten, you risk damaging the bottom end .If you tighten the clamp before you skip the alignment process and you won’t benefit from plugging the plug. The video shows a visual representation of the axle installation procedure that Westfeldt describes.
Rotor engineers wanted to simplify things even further. “In an ideal world, the bolts would be the same, but people would worry about checking the bolt tightness every few thousand kilometers, and if the bike was heavily used, they would change them every year.”
In Cotic Cycles, this shift will be about being lighter and stronger at the same time. “If cost didn’t matter, I would always use Ti fasteners instead of steel because it saves weight, but it’s hard to argue for value for money!”
All those tests and torque specs don’t always work when we jump. We are quite active mountain biking and sometimes things break or come off. We made sure to ask everyone about the problems caused by their fasteners.
Ibis Ibis staff shared a story about excessive use of thread locks on some frames. “We had a problem where I built all the prototypes with one drop of Loctite per bolt and they all came apart perfectly. Then we had a production man who thought he did a really good job of carefully coating the bolt and nut threads with Loctite Well. . suddenly people can’t take the frame apart without damaging it. Now our frame assembly SOP [standard operating procedure] is much more specific.”
The problem of tightening various components sometimes arises as the industry changes and not everyone has immediate access to the required torque information. On NS bikes, the problem was with the dropper post on some of their models. “With the rapid development of products and technology, we ran into some challenges. It was really hard to avoid. One of them was the introduction of seatposts into the industry. Given our bulletproof trail bike, we tend to over-tighten the seatpost clamp, which can lead to reduced performance. Once we identified the problem, we entered the [torque] procedure.”
Last but not least, the Raaw bike had to increase the torque a bit to cope with the forces exerted on its lusciously gravity frame. “We had to increase the torque at the main pivot because we underestimated the required downforce,” Torenbeck said.
These are the basics of it. See you on singletracks on the next edition of Riding Rainbow!
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Fix it, ha! I love that companies are thinking about the tools we already have, even though the number of shapes and sizes seem to have increased over the years.
I’d rather have plums everywhere. Considering the cost of mountain bike components, I think one could spend the money on a set of Torx wrenches as well. Better than dealing with a stripped hex head (well, it can happen with Torx too, the last time I used my bolt extractor was for disc brake screws). The excuse that the bike’s screws are not available… that’s just an excuse in my opinion. Just my 2c
Post time: May-10-2023