I'm not going to show you yet.
I have walked a tight rope during my life in the bike world. On the one side, I was raised and educated as an engineer - so I value innovation, technology, and design. On the other hand, I am a farm boy - pragmatic, frugal, and I love when I can get the job done well without excess.
That rope is really, really thin in this industry. It needs to work for the purpose I need it to; it needs to be cost effective and simple. In order to have it work for the purpose I need it to, it typically isn't cost effective or simple. Those two concepts have been presented to consumers as mutually exclusive. I came up against a moment, a long time ago, where I wanted to go faster on rougher trails, but I wanted to maintain control of my bike too. This meant that I needed to get a full suspension bike. The moment I crawled out of the bmx scene as a youngin' and discovered for myself the wonder of mountain biking - then got to throw a leg over the space-age technology of full suspension bikes: I was hooked. Since then, I've owned probably two dozen different types of full suspension frames, and have ridden hundreds.
If the bicycle is the noblest invention, the full suspension mountain bicycle is the rowdiest invention. You say you want the bike to facilitate going faster despite the terrain being unpredictable and violent? Check. You want to be able to reduce the amount of harshness that your body has to absorb from the ride? Check. These bikes have largely been made out of aluminum or carbon, and I had to sit down myself and ask why. So I'm gonna tell you a bit about what I know.
Let's talk about suspension - it's purpose, basic terminology, and the myriad of convoluted system designs out there.
When you take an object and give it the ability to travel in one or more directions while maintaining it's physical connection to other objects, you have suspended it. When the suspended object moves in a controlled direction, it has travel. If you somehow restrict that object's movement in one or all of those directions in order to absorb the very energy that is making it move that direction, you have added damping to the suspended object. If you do the same but with a component that continuously resists the movement by presenting equal and opposite force until it can't anymore, you have created a spring.
It is very important to note that damping, spring, and travel can be related to either a component that controls all of these, such a shock, or it can relate to the material of the object that allows it to deform/conform. (or it can be both).
In a suspension fork, the object that is allowed to move is the "lowers", which is the part of the fork that the wheel attaches to. It's all much simpler, as the lowers can only travel in one direction.
With a suspension frame, it gets a bit more complicated. The rear wheel on a suspension frame is typically connected via one or more parts to the frame, and those parts in motion can compress a shock (like a fork but smaller).
Regardless of whether you are talking about a fork or a shock, the actual path that the axle makes is called the axle path, and is most commonly used to describe the amount of travel a suspension system has.
The process by which force is pushing the suspension inward is called compression. When suspension is fully compressed, it's called bottom out.
The process by which the suspension is pushing back is called rebound. When a suspension is fully rebounded, it's called top out, or just uncompressed.
The purpose of suspension is several fold.
Traction: By constantly compressing and rebounding over terrain, your suspension does it's best to keep your tires contacting the ground, which means you have consistent traction, and thus, control. (Passive attribute)
Absorption: This can be as simple as reducing the harshness of the terrain on a person's body. The energy that would normally travel up into the rider would essentially get turned into heat in the suspension. (Passive attribute)
Performance: When the suspension is designed and tunes particularly well, it can be used as an extension of the riders abilities, and thus manipulated in such a way that it can amplify what is possible for them on any given terrain. (Active attribute)
There's a LOT more to it than that, but the concepts above should get you going.
Pretty simply, when you ride any kind of terrain, there are forces that are being absorbed by the bicycle and your body, any forces that are greater than your bicycle can absorb get transferred to your body. The more unpredictable the terrain, the more energy will inevitably get transferred to your body. The faster you travel, the harsher and more unpredictable that energy will be. The more energy transferred to your body, the less control you will ultimately have over your bike. Suspension will reduce the amount of energy that your body needs to absorb, so that you will have better control over the bike during those moments.
So it should be a little clearer what a suspension bike needs to do, it allows the rider to ride faster and more controlled over varied terrain.
Now let's talk about materials.
Generally speaking there are only a handful of materials that companies use to make bike frames, and they all share a key similarity in that they are all simply appropriate enough for the intended use of bike riding, but beyond that they are all pretty different in their attributes and characteristics that they bring to a bike.
The main ones are: Carbon Fiber, Titanium, Aluminum, and Steel.
There are a lot of people in the bike industry who want you to believe things about each of these materials for one reason and one reason only - so they can sell more of the product that they make out of that material. Luckily for you, this is just a humble blog, and I'm probably not going to try to sell you anything. All I am going to do is tell you about an epiphany that I, and others in the industry have had about the crap that's been shoved down our throats about frame materials. I'll talk briefly about the material itself and then we'll start comparing them and why they are good for what.
Carbon Fiber: This material makes use of millions of small carbon threads that are made into a fabric, that fabric has epoxy applied to it's surfaces, it is combined with other fabrics, then compressed into a specific shape and heated until the epoxy cures. The process of layering sheets of carbon is called lay up. Think paper mache, but fancier. By itself, the carbon fiber fabric is not particularly amazing, it literally just feels like a heavy fabric, like a shiny black canvas. This fabric can be woven in a variety of ways to achieve different attributes. At the end of the day, it's the epoxy that makes the carbon fiber strong in the ways that the products intended purpose is meant to need. Most commonly, carbon is used where there are large, relatively simple surfaces that would benefit from having a high strength to weight ratio. Think airplane wings, car hoods, etc. Due to the variety of lay up styles, carbon can typically be used to produce a wide range of characteristics. Carbon is generally not recyclable.
Titanium: Also sometimes referred to by only it's periodic abbreviation of "Ti", this material is known for it's very high strength to weight ratio. It is a fairly expensive material to work with. It has a super high melting point, so it is excellent in applications where heat resistance and weight is key. Ti has a lot of very attractive properties for bike frames, corrosion resistance, compliance, strength, and it is lightweight to boot. Where Ti does not shine is it's durability, fatigue resistance, and it's price tag. Rarely if ever do companies use pure titanium, it's often an alloy of several metals. Because of this, it is possible to have a good range of characteristics based on the blend of the alloy. Most commonly used in aircraft engines, and the medical industry. Ti is recyclable.
Aluminum: Very often labeled just as "alloy", which is silly because that word simply means that it is a mixture of several metals - and just about every metal we use in todays world is an alloy. Hell, bronze is an alloy. Anyway. Aluminum has an incredibly high strength to weight ratio. It is incredibly stiff, and because of that stiffness, aluminum is exceptional at transferring energy. Most of the aluminum alloys are relatively soft metals, which means they are easy to deform and don't have a good "memory"; more on that later. It can corrode, but is fairly resistant to it. Aluminum is often used in construction, electronics, and automotive applications. Aluminum alloy is recyclable.
Steel: Like the other metals on this list, steel is an alloy of several elements. The difference is that steel describes only an alloy. Where technically you can have raw versions of any of the above. Iron and carbon are the two parts that make steel, and other elements can be added for different characteristics. Steel is incredibly durable, has a strong memory, and has excellent fatigue resistance. Steel is not particularly light weight, although in most of it's applications, weight doesn't much matter. Because of it's iron content, it is susceptible to corrosion, however with the correct treatment - corrosion can be mitigated. There are a lot of different types of steels, with many different applications. Steel is very hard, and resists deformation very well. It is most often used in construction, automotive industries. Steel is recyclable.
So why are we taking a material physics class right now? As mentioned above, it's important to understand the basics of each material before we can understand why they may or may not be good for bike frames.
Material Riding Characteristics
A bicycle has forces applied to it from a lot of directions, and as a result, most materials will absorb some amount of that energy, and whatever they don't absorb, they transfer. Absorb is being used liberally in this sense, because it's not like the material is a sponge. It's not the black panther's suit. Bike frames have a very hard job to do, they need to be stiff where we need them to be (but not everywhere), compliant where we need them to be (but not everywhere), we need them to be durable (everywhere), and we also want them to be light weight. Notice how I used the word, 'want' instead of need on the light weight part. More on that later.
Stiffness, Compliance, and Durability
Stiffness in this sense is how well a shape is held, despite outside forces. Think about a piece of plywood that doesn't bow if weight is applied to the side. Stiff material generally transfers energy really well and doesn't absorb much.
Compliance here is about how well a shape can flex, to a point, with outside forces. Think about the same piece of plywood but how it can bend when the forces are applied to the wide surface. Compliance is where the energy is absorbed.
Durability is how well the the material stands up to impacts, and fatigue, though more on fatigue later. Generally a soft material is not very durable. In the plywood analogy, it's how well the plywood holds up to being bent often, or how well it holds up to a hammer.
Carbon is interesting in this sense, because ultimately the layup can allow it to be very stiff with certain forces, and very compliant with others. Carbon is very good at absorbing/dissipating vibrations, but is not good at absorbing impacts (it has low hardness).
Titanium is very good at absorbing energy, it can be stiff, but is mostly known for being compliant. It will not absorb impacts well.
Aluminum is not good at absorbing energy, it is very good at transferring it, it is exceptionally stiff. It does not absorb impacts well, however, it has excellent memory. So a tube can have a dent in it, and in most cases the dent does not compromise the structural integrity of the frame, nor does it always effect the geometric integrity (alignment).
Steel is very good at absorbing energy, but it is also very stiff. It can be compliant as well. Steel is exceptional at resisting impacts, and similar to aluminum, even when dented it can hold it's integrity.
In point of fact, while it may seem from above that some materials are favorable above others, but that isn't the case. They all have pros and cons, and subsequently each genre of riding has material characteristics that are better suited than others. For example, BMX racing requires the rider to have exceptional control over the bike, so every input from them needs to be translated into the bike - a material like aluminum or carbon would be ideal for that because they can be so stiff, and a bike being light weight can also be helpful here. If you take a material that is best suited to one type of riding and you apply forces to it beyond that which would be expected by that genre, and it breaks - does that mean that the material is weak? No.
Modulus, Fatigue, and Failure
Lifetime warranty is a funny term. Very often you'll buy a bike and you'll see it comes with a "lifetime" warranty. I've worked in warranty management for several manufacturers; read the warranty and you'll find that what they mean is that the product is under warranty for the lifetime of the product, not your lifetime. Those companies are counting on your assumption that it means your lifetime. Most of the time, "general wear and tear" are also not subject to warranty.
Modulus is a term used to describe the range of force that can be applied to a material before it fails. There are several parts to this range, each with their own names and descriptions. To make this simple, we are going to omit the first two, which indicate the amount of force a material will take before it starts to flex. We are going to talk instead about the point where it starts to flex, and the point where anymore flexing would compromise the material and cause a fracture of some kind - leading to the failure of the product.
Why do I bring this up? Because one of the qualities that every material shares, is entropy. No material will cease to fail at some point for some reason. In the bike industry, we have long had "wear parts". These are parts that in terms of the life of the total product (the whole bike), will wear out sooner than later. These are chains, cassettes, chainrings, wiper seals, bearings, pulleys, grips, etc. And lately, bicycle frames have slowly but surely become a wear part.
So let's take a look at our materials, how they fatigue, what it takes for them to fail, and that failure looks like.
Carbon has good fatigue resistance, despite it's softness. No fatigue is occurring during that time between where it starts to flex and just before the point of facture. The epoxy that holds the carbon, has a very low modulus. It is very brittle. There is no formula for this, as each lay up is different. It should be noted however that usually it is the epoxy bond that fails before the carbon itself fails. Due to the nature of carbon manufacturing. It has a fantastic memory, which describes how well a shape returns to normal after stress. This is deceptive however. Carbon that has failed can also return to normal.
A failure in carbon can happen a few ways, but it ends the same regardless of how it started. The most common way is an impact, this is the bane of carbon fiber. The impact can be with a rock, a root, a tree, a car door - anything really. What the impact has done is pushed in on the fiber so much as to cause a failure in the epoxy bond. Once this bond has failed, the frame is no longer safe to ride - however it is unlikely to show it on the surface. The frame will likely ride the same after that, the failed bond will suddenly require more support from the surrounding frame structure, and as those parts support more than designed to, they begin to strain. Failure will be all of the sudden, and catastrophic. That is to say, one moment you will be riding a solid frame, the next you won't. Another way carbon can fail is through fatigue, although you could argue its the same, just slower to build up. If a frame is flexed past it's maximum enough times, epoxy bonds will start to fail, and the same thing will happen. Part of the difficulty in engineering a carbon frame is that its nearly impossible to know exactly what forces the frame needs to be able to hold in that flexible zone. Carbon failures can sometimes be repaired, but it's costly.
Titanium has okay fatigue resistance, it's soft, so it will lose integrity over time. It is very stiff, so getting it to the point of flex takes a while. But once it is there, the range it has before the maximum is low. A titanium failure starts in the form of a crack, this can come from a fatigue, or from impact that dents or gouges - specifically with a "crease" to the damage. When the crack is only on the surface of the material, nothing changes for the frame in terms of ride quality. Once the crack reaches through the thickness of the material and starts to travel along the length of the material, almost like a molecular zipper, the frame will begin to creak and pop as stress is applied to it. This is true of all metal frames. Cracked frames warn the rider of failure. Ti will not return to form after failure. Titanium can sometimes be repaired.
Aluminum has a similar fatigue resistance to titanium, but it has the benefit of being machined easily so that complex shapes are possible that effectively reduce fatigue. A failure in aluminum is the same as any metal frame, it starts as a surface crack and works its way through. Aluminum will not return to form after failure. Aluminum cannot be easily repaired.
Steel has excellent fatigue resistance and excellent memory. The range that steel can flex before it's point of failure is very broad. It's point of failure will cause the same reaction as other metals, surface crack, leading to material fracture. Because of steel's hardness, failures will usually not come from impacts and instead usually from fatigue at the welds, as they are usually the weakest link. Steel will return to memory after failure, but with an obvious lack of integrity. Steel is repairable.
Why does all of this matter?
Simple: mountain biking is ALL about energy. What your bike does with energy will dictate how the bike feels to the rider, it will dictate how long the bike will last, and it ultimately it will dictate how well you'll be able to ride. Different components need to do different things with energy, and such, it should be clear by now that different materials do different things with energy. So if you can pick the right materials for each component, it is possible to find a harmonic balance between all of those materials to create a well riding bike that lasts a long time, and that you can use for a lot of varying terrain.
Great but we meant why does this matter for a write up about your bike?
Well I know I said I probably wasn't going to try to sell you anything, and that is true, but by now you should have sold yourself on two things:
1st: Steel is by far the best material to use for a mountain bike frame.
2nd: Carbon is by far the least sensible material for a mountain bike frame.
I say sell, because at least right now I'm certainly not trying to sell anything, but you should absolutely pry yourself away from the marketing of larger companies who insist carbon is the only material that makes a great bike, they are in the business of selling bikes and selling them often - it makes no sense to sell you a frame that will last a long time. Frames have become a wear part. They may spout off a bunch of nonsense acronyms and make it seem like their lay up process makes them vastly different and special. They are counting on you crashing your frame, and either needing to buy a crash replacement frame (which gives them the same margin as if they sold it to the dealer, so no problem for them), or that you'll buy a new one all together. They also would have you believe that you need an ultra light high performance frame, but they have to add so much material that it ends up not really being all that light weight. I've got news for you...
They are full of shit.
This is my new full suspension bike, made out of 4130 steel. I designed it from the ground up to meet my needs and wants as a rider. If weight is important to you, it weighs 33lbs with a heavy build. It has 148mm of travel on the back, and 150mm on the front. This has been the single most fun mountain bike I've owned. At this point as I've mentioned, I've had dozens of carbon and aluminum mountain bikes, from premium to mid level. It climbs beautifully, descends confidently, corners like it's on rails, jumps like it's all it wants to do.
I have the brand and name blurred out because they are my brand that I am contemplating building.
I am still testing this frame, and I have a new prototype on the way, so a full review will be coming soon.
This write up is designed to give you a base level of knowledge about suspension and materials, which in reality is the level of knowledge that you should have when you are shopping for a full suspension bike. Once you understand these concepts, you'll be able to make a more informed decision about your purchases, and make those manufacturers work a little harder to win your sale.
They LOVE when it's easy.
コメント