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Saturday, 13 August 2016

Understanding Your Bicycle Frame Material

Which Material Is Right for You? It depends. Many factors—your style of riding, your weight, your sense of adventure—all play a role in your choice of material. The following paragraphs explain the different types of material commonly used, pros and cons, and riding characteristic. I hope you can choose which materials suitable with yourself after read this article. A few bikes out there are made of exotic materials (like a bamboo), but that's another discussion entirely. 

Carbon (High-Tensile) Steel and Chromoly (Chrome Molybdenum)

Steel is real! Steel is the most commonly used material in bike frames, it  has been used by frame builders for over a century. Steel is durable, totally resistant to fatigue stress (when used for standard bike riding anyway) and easily repaired. Carbon or high-tensile steel is a good, strong, long-lasting steel, but it isn't as light as its more high-tech brother, the steel known as chromoly. All steels have the same inherent stiffness and weight, regardless of strength - Reynolds 853 is no stiffer than 1010 (mild steel). Adding a tiny bit of chromium and molybdenum makes it strong enough to “butt” or thin down in the middle, thus making it lighter. This alloy is usually referred to as chromoly.

Most quality steel frames use a variation of chromoly. This principle of engineering frames to use less of a stronger, stiffer material is true for all frame materials. The materials themselves are not lighter; the way they are used allows the builder to use less material to build a stronger frame. At one time nearly all high quality frames were steel chromoly. The recent development of very high strength “air-hardened” steels (like Reynolds 853 or True-Temper’s OX-Platinum that gain rather than lose strength as they cool from welding) has made for frames that have a strength-to-weight ratio equal to titanium frames. A popular quality steel for bicycle frames is American SAE 4130 steel, better known as "chrome molybdenum," and referred to as "chromoly" or "chrome-moly." And, there are plenty of other impressive alloys offered by tubing suppliers such as Columbus, Reynolds, Tange and True Temper.

The strength of any type of steel allows builders to engineer a certain amount of flex by using thinner tubes which translates into what riders call a “lively” feel or springiness, something builders using aluminum can’t do because when aluminum flexes it fatigues the metal, which ultimately can lead to failure. Steel frames are also relatively easy and cheap to repair, and the technology has been around for a long time.

Which steel is best? There are many different names and numbers you'll see thrown around - Columbus, Reynolds 531, 725, 853, Cromo 4130, and so on. The differences are quite technical, but they usually come down to relative strength, hardness, and the properties of the metal when it is heated (during the welding process). The thing is, metal usually gets weaker when it's heated up, which is not a good thing around the joints (where welding and brazing applies heat). But some steels are made to deal with this - for example, Reynolds 853 tubing is "air hardening", which means basically that 853 is very well suited to TIG welding, since it actually gets stronger at the weld points. One downside, however, of 853 is that it's very hard, which means it is also harder to work the metal. This is why most beginner framebuilders will use a softer steel, like 4130, which is commonly used in the aerospace industry.

Pros and Cons
+ Cheap raw materials and manufacturing cost. Ride quality and comfort of high quality steel is second to none. Durable and impact resistant. Will bend rather than snapping suddenly. Relatively easy and cheap to repair damage.

- Is probably the heaviest of the four main materials. If made too light or of disputable quality then the frame can be excessively flexible. Steel tubing will be round so no aero profiling. Can rust and may need occasional re-sprays.

Riding characteristics
Frames built of these materials are famous for their combination of responsiveness and comfort. Steel is the standard that other materials are compared to. It's got a lively, comfortable ride that most customers prefer.


Aluminum

Having come a long way from the oversized tubes of old, aluminum is now less expensive and very widely used on today's bikes. Aluminium is lighter than steel (when comparing an equally sized tube), but also weaker and is susceptible to fatigue stress and failure over time. With proper design it can give a solid ride for climbing, or lively handling in tight situations.  Aluminum introduced as a material for bicycle frames about 30 years ago, aluminum is now the most common material. It is less dense than steel, so it results in lighter frames. Because of its decreased density, it requires larger tube diameters to achieve enough strength for a bike frame.

Aluminum doesn’t oxidize like steel (read: rust). Their lateral stiffness gives aluminum frames a quick feeling because the transfer of pedaling force is so immediate, but some complain that the same stiffness translates into a lack of vertical compliance, making for an unforgiving, harsh ride. This effect is ameliorated to some degree by the now-common use of carbon fiber forks and suspension to soak up road shock.

An aluminum frame can be made stiffer and lighter than steel because it is not nearly as dense. This is done by increasing a tube’s diameter while maintaining the wall thickness, making a tube that is eight times as stiff, but only twice the weight. This “oversizing” of tubing runs the risk of a “beer can” effect if the tube walls are thinned too much. Aluminum’s affordable lightness and stiffness make it the first choice these days for bikes with any kind of suspension.

And, like steel, as you spend more, you get higher quality tubing and better construction. The buzz about aluminum is that is has a more jarring ride than the other materials. But, while this used to be the case in its early years, it's not a problem today thanks to new aluminum alloys, tubing enhancements and improved construction techniques. These allow the frames to absorb shock better than ever while still offering the wonderfully lively ride that makes aluminum all the rage today.

This magic ride is attributed to aluminum being the lightest frame material -- even lighter than carbon and titanium. It makes aluminum frames great choices for racing and time trialing. And, unlike steel, aluminum won't rust; another advantage. There are various types of aluminum tubing in use by manufacturers. Some common types are 6061 and 7005, numbers that refer to the alloys in the aluminum such as magnesium, silicon and zinc (pure aluminum isn't strong enough for bike use). And, there are some new superlight tubesets such as Easton Scandium.

Pros and Cons
+ Can be super light-weight. Fairly cheap manufacturing costs and easy to mass produce. Generally stiff offering excellent power transfer. Pretty tough. Modern tube shaping techniques such as hydroforming can fine-tune strength and ride feel.

- The stiffness and rigidity can result in an overly harsh ride. This is why you’ll often find a carbon fork and seat stays on a top end aluminium frame. Can corrode and can react adversely with carbon fibre components. It will weaken over time. Hard to repair.

Ride Characteristics
For the most part, oversized aluminum frames are very stiff and unforgiving. You'll get good transfer of power through the cranks to the wheel, but suffice to say that the 'thud' sound you hear if you flick the frame with your finger nail, is the same 'thud' sound you'll feel when riding on pavement or bumps. You'll feel the road transferred to your 'contact points' through a very unforgiving frame. Tight corners on bumpy roads will require more slowing down for control purposes as the bike can 'bounce' or 'rattle' out of the groove if your not careful. Not to characterize all modern aluminum bikes the same though, Scandium aluminum from Easton claims to ride more like a steel frame. 


Titanium

Lighter than steel but just as strong, this more-expensive metal is found on high-end road or cross-country mountain bikes. It flexes so well while maintaining its shape that some very high-end bikes use the metal itself as a shock absorber. Many cyclists and experts feel that it combines the best characteristics of all the other frame materials. It rivals aluminum in weight, is as comfortable as steel and it has a sprightly ride and electric handling that many riders swear by.  Titanium has an excellent balance of properties for frame building, combining durability with lower weight. Titanium alloys are half as stiff as steel, but also half as dense. The strongest titanium alloys are comparable to the strongest steels.

Stiff titanium frames need larger-diameter tubes than comparable steel frames, but not as big as aluminum. Titanium is very corrosion resistant, and very light frames can be made stiff enough and strong enough for bigger riders. Most Ti frames are the 3Al/2.5V alloy (3% aluminum/2.5% vanadium), with the more difficult to use, 6Al/4V (6% aluminum/4% vanadium) falling out of favor with most frame builders. 6Al/4V is more expensive, lighter, harder to machine and stronger.

As an element, titanium is one of the most plentiful elements in the world. But titanium frames are expensive not only because of the material costs, but because Titanium is hard on metalworking tools, requires expensive titanium welding rod and must be joined carefully in a controlled environment.

Pros and Cons
+ Very high strength to weight ratio. Rustproof and bombproof. Doesn’t even require painting or lacquering. Can rival steel in terms of ride quality. High resistance to metal fatigue.

- High price raw materials and extremely labour intensive and skilled frame building process makes for a hefty price tag. Bigger or more powerful riders might find the really lightweight frames a bit too flexible. Also, some people find titanium prone to “twitchiness” and “speed wobbles” when descending. Hard to repair.

Riding characteristics
If the frame is built heavy enough for the rider, then the riding characteristics are fantastic. Ti frames ride smooth and responsive and stable. The frames feel "alive," as if each pedal stroke gets a boost from an inherent springiness in the frame. 


Carbon Fiber

Carbon fiber is a relatively new material and unique because it's not a metal material. Is made up of non-metallic graphite fiber cloth that is layered together with high strength epoxy resin to form a matrix. Originally used in the aerospace industry, it can have a high strength to weight ratio, but it is quite expensive. Individual fibers of carbon are tremendously strong and stiff, but they are useless unless arranged in a strong pattern, and held together with a strong “glue” (usually epoxy).

Unlike metals, in which strength and stiffness properties are nearly the same in all directions, carbon fiber composites can be tuned to orient the strength where it’s needed (for instance, stiff laterally and compliant vertically). This makes carbon fiber the preferred material of choice for unconventional frames and shapes, as it can be molded and tuned more than any metal. So why aren't all bikes made out of carbon fiber? It tends to be brittle. The fact that metal can bend and regain its shape is what makes it last. Because of this, carbon fiber bikes are built even stronger than needed.

Like titanium, because construction is somewhat complicated and because carbon fabric and resins are costly, carbon frames are on the high end of the cost spectrum. To describe these frames manufacturers use terms such as "high modulus" and "void free," which tells you that it's high-quality carbon fiber material and stellar construction. Sometimes, these designations appear on frame "tubing" decals.

Carbon fiber will not corrode, but it does require greater care than bikes made from metal and may not be as durable long term. A deep scratch or hard knock can damage the integrity of the structure creating the danger of a major failure.

Pros and Cons
+ Very high strength to weight ratio, giving rise to the lightest bike frames available. Excellent resistance to fatigue and totally corrosion resistant. Strength, stiffness and ride characteristics are controllable during the manufacturing process to give exactly what is required for the requirements of the riding and rider. Can be moulded into any shape making highly aerodynamic designs possible.

- Expensive raw material. Resistance to accidental knocks and the effect of apparently minor scratches and dings on structural integrity can be a concern. Can break suddenly (if weakened) without warning. Particularly prone to those of us who can be over zealous with an allen key. Hard to repair. Quality of lay-up can vary massively.

Riding Characteristic
Maybe carbon frame can have all riding characteristic from all metal material above. It can be a very stiff but a forgiving too. Right words to describe it is a "Tailor made" frame for (almost) all you want from bicycle frame. 


Every material had a pro, cons and unique riding characteristic. Nowadays, frame builder not only use a one material to build a frame, sometimes they mixed up different material in one frame, like titanium lugs with carbon tubing or aluminium frame with carbon seat stay etc. Now you had a knowledge to determine which one frame suit for you. Get out there and buy the damn frame.


Source:
https://www.rei.com/learn/expert-advice/bike-frame-materials.html
http://bigshark.com/articles/which-frame-material-is-the-best-pg531.htm
http://www.rodbikes.com/articles/material-world.html
http://citybikes.com/articles/road-bike-materials-pg57.htm
http://www.bikeroar.com/tips/frame-materials-and-what-to-buy
https://www.crazyguyonabike.com/doc/page/?page_id=8364
https://www.britishcycling.org.uk/knowledge/article/izn20131118-All-Cycling-Frame-Materials-0


Ride On!





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