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Introduction: Bicycle Design
Why Upright Bikes?
Why Recumbents Cost More
Types of Recumbents
Seat Height
Handlebars
How Much To Spend?
The Importance of Wheels
Types of Wheels
The Importance of Weight
Frame Materials
Frame Alignment
Parts, Derailleurs etc
Brakes
Suspension
Are Recumbents Invisible?
Acclimatizing to a Recumbent
Hills on a Recumbent
Clip-On Pedals
Racks & Mudguards
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How to Ride a Tandem
Credit Card Touring
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Bicycle Frame Materials

Carbon Fiber
Steel
Titanium
Is Titanium Worth the Price?
Aluminum

Four popular bicycle frame materials are steel, aluminum, titanium and carbon fiber. Beryllium, Metal Matrix Composites and other materials have so far demonstrated limited practicality in bicycle frames. Mysterious and seemingly miraculous beryllium is one-third the weight of aluminum and six times as stiff as steel. Beryllium, however, is very toxic during the manufacturing process and there are probably no safe levels of exposure to the particulate form of this metal.

It is sometimes a matter of opinion as to the particular suitability of different types of materials to different types of bicycle frames.

Unlike automobiles or motorcycles, the frame materials in bicycles are pushed to their absolute limits in order to reduce minute amounts of weight. Any bicycle frame can be made stronger by adding weight. The trick is to come up with a reasonable compromise between weight, performance, durability and resistance to damage. The compromise will be different for a professional bicycle racer and a person who uses their bicycle for club racing, commuting, grocery shopping and touring.

The professional cyclist only has to finish the race she is in on that day because the bicycle manufacturer is providing her with an unlimited supply of replacement frames. The professional racer also has a professional mechanic who follows her in a car and closely examines her frame every night. A normal cyclist needs a more durable frame that will stand up to the rigors of normal use and abuse without having to be coddled by a professional mechanic.

Many people have mistakenly purchased ultra-light frames expecting them to last longer than a few seasons of category 1 or 2 racing without breaking. At one point, some mountain bike manufacturers were supplying frames so light the frames would not even last a season of amateur racing before failing.

Carbon Fiber

“Carbon fiber” is a catch-all term used to describe various different composites that include different polymers, carbon and graphite that are held in an epoxy-resin matrix sometimes containing metals or ceramics. Advanced composites offer great possibilities for light weight and high-performance because layers of composite can be placed only where they are needed. Fibers or whiskers of material can be oriented within the composite to stabilize dynamic forces to different degrees and directions on different parts of the bicycle frame.

The semi-metallic element boron is currently all the rage in carbon fiber frames.

One holy grail of the composite frame designer is to achieve lateral stiffness and vertical compliance. On the other hand, critics claim that the forces on bicycle tubes occur in so many different directions that the anisotropic (directional) qualities of fiber strength and stiffness can only be advantageously utilized to a limited extent in a bicycle frame.

Most bicycles manufactured with carbon fiber composites require a degree of care and attention to stand vigilant against damage that could lead to a sudden and catastrophic frame failure (an especially important concern on a tandem where a lot of speed and weight are involved). Carbon fiber frames and forks are not idiot-proof. If the exterior of the frame is not protected by a layer of protective material, such as Kevlar fiber, surface damage to the outside layer of the composite can propagate beyond the area of initial damage. Similarly, damage to the interior structure of the composite can also lead to failure. Hidden damage is most insidious precisely because it cannot be seen.

Failure would not be an issue if bicycles were not subject to abuse and cyclists closely examined their bicycles for any signs of damage. However, surface damage can result from the normal everyday use of a bicycle, when it is leaned against another bicycle, loaded on top of a car or into a train or when it is dropped. Hidden damage can result when frame members are inadvertently overstressed through normal abuse. Ramming a curb, riding through potholes, airline baggage handling and falling over a loaded touring bike while stopped could all lead to hidden damage that could later cause a sudden failure.

At certain points, the carbon fiber parts of a frame must be joined to metal parts. Joining dissimilar materials can lead to problems that carbon fiber bicycle builders are working to overcome. Three issues arise when joining carbon fiber to other materials: thermal expansion differences, galvanic corrosion and discontinuity.

Different materials may expand at different rates and shear or fracture joints when the temperature of the materials changes. Titanium has similar thermal expansion rates to some carbon fiber composites, while steel and aluminum have different coefficients of thermal expansion than carbon fiber.

Galvanic corrosion arises when dissimilar materials are placed in close enough proximity to each other to undergo an oxidation-reduction reaction that can weaken or destroy the joint. Aluminum and carbon fiber have different galvanic corrosion potentials that will result in such an electrolytic reaction if the two materials are not insulated from each other. This is another reason to look for metal frame parts (such as dropouts) that are made of titanium rather than aluminum if you are shopping for a carbon fiber bike.

Discontinuity of materials can create stress-risers where the carbon fiber meets the other material. The stress-risers can lead to failure. The termination of the carbon fiber frame part can contain points where matrices of woven, stranded and free anisotropic fibers are broken and may develop weaknesses that propagate from the sharp termination.

Keep in mind that these opinions cannot be universally applied to all composite bicycle frames. There are many different types of composite materials and many different methods of composite frame construction. Some composite frames have more idiot-proofness built in. The outside layer can be made more impervious to notch failure and material can be added to resist stress failures within the frame material.

Many cyclists have developed a particular taste for the ride qualities of some composite frames. Some composite frames are especially adept at absorbing high-frequency road vibration that tends to affect very light cyclists.

"Fast Freddy" Markham once had this to say about carbon fiber:

Carbon fiber is best. You simply cannot engineer an alloy tube to do what you can with CF. Not only is CF much lighter, but is also stiffer stronger and absorbs vibration better than any metal. It also has a longer fatigue life than other materials. Carbon fiber also makes an effective spring, allowing the frame to act as a shock absorber.

Fast Freddy knows how to ride a recumbent. He set a world speed record on a metal recumbent similar in configuration to the new carbon fiber Calfee Stiletto

Steel

Steel is the material of choice for many bicycle frames. Bicycle builders have had many years of experience refining the designs of steel bicycles and tubing suppliers have developed high-performance alloying and shaping techniques for bicycle tubing. Incredibly light and durable bicycle frames can be made from steel tubing. Steel offers a comfortable ride and a steel bicycle frame can act as a spring to store energy when the rider causes the frame to flex at different parts of the pedal stroke. That stored energy can then be released and converted to forward motion on another part of the pedal stroke.

Steel bicycles impart a certain level of confidence in the ability of the bicycle and for that reason steel is the material of choice for many professional bicycle racers. For many applications, steel frames provide the ideal combination of performance, durability and purchase cost. Steel frames can be inexpensively repaired and steel has the ability to reveal frame stress injuries before they become failures. When a steel bicycle frame breaks, it tends to break slowly rather than suddenly, catastrophically and without warning (unlike aluminum frames).

High-quality bicycle frames are made of steel tubing that has been alloyed with chromium and molybdenum (hence the term “chromoly”) or sometimes manganese and molybdenum. The tubes can be joined using lugs and some tubes may be welded or fillet-brazed. Fillet-brazing is not a common joining technique these days, although many quality tandem frames have been fillet-brazed in the past.

An upright bicycle frame that has been brass or silver-brazed together with finely-crafted cast lugs is an object of technological and esthetic beauty. Despite the current popularity of welding lugless upright bicycle frames, a well-constructed lugged upright single bicycle frame constructed by a skilled framebuilder is an object much sought after by knowledgeable cyclists who are seeking excellent performance in a bicycle frame. For upright single touring and racing bicycles, quality lugged frames have not been overtaken in performance by the welded, lugless frame.

The steel tubing that is used to build quality recumbent bicycle frames is usually 4130 chromoly which contains about .75% chromium, .25% molybdenum and .3% carbon. 4130 chromoly is a proven staple in aircraft manufacturing and is available in the length, diameter and wall thickness required by recumbent bicycles. 4130 is a magnificent metal that makes it possible to build strong and light recumbent frames that have outstanding performance characteristics.

Recumbents and most upright tandems are welded because the tubing used on these types of bicycles allows welding with no loss of performance over a lugged and brazed frame. Mountain bikes can be built without lugs for much the same reason. Some of the frame joints on recumbents would not be suitable for lugs under any circumstance.

Some older upright tandems were manufactured with lugs but tandem builders began using larger diameter tubes and different tubing configurations for different sizes of frames. Lugs were not available for the newer configurations and bigger or ovalized tubes so the frames were fillet-brazed or TIG welded. TIG welding was found to provide a strong joint and very low weight. TIG welding is now the preferred method of tube joining for most tandem builders.

Tungsten Inert Gas welding (TIG welding) is a wonderful technology that allows for a multitude of tubing configurations in recumbent bicycle frames. TIG welding is a type of arc welding where a filler metal is hand-fed into a very small arc that is advanced around the circumference of the joint by the other hand of the weldor.

The filler metal is fed into the liquid weld pool in wire form. The welding torch is about the size of a pen and is usually controlled by a foot pedal. The arc takes place in an inert gas shield (usually argon) that is supplied through a gas line built into the torch itself. TIG welding machines used for bicycle frame welding are the most sensitive and sophisticated arc welding machines available.

Titanium

Titanium is the ideal metal for recumbent bicycle frame construction. A recumbent frame made of titanium can be slightly lighter than steel yet provide even more strength, resiliency and fatigue life than steel. Strength is especially important on a tandem bicycle frame because of the large amount of weight the tandem frame must carry and also because of the very large dynamic forces produced by a pair of cyclists on a single bike. Strength is even more important on a recumbent tandem because recumbent cyclists are not in a position to unload their own weight from the bicycle while riding over bumps.

Titanium is impervious to the elements. The surface of titanium requires no finish. A titanium frame will last virtually forever with little or no care. A titanium frame will withstand many more fatigue cycles before breaking. Titanium is tougher for baggage handlers to damage than steel.

A titanium frame can undergo an expensive polishing process to produce a lustrous and shiny surface but the polishing adds nothing to the performance of the frame. The most practical finish for a titanium frame is the beautiful satiny finish produced simply by a 3M Scotch-Brite pad.

Like steel, titanium has the ability to store energy and release energy at different degrees of the pedal stroke. Titanium frames also have very pleasant riding characteristics because of the unique acoustic properties of titanium. A titanium frame will absorb a lot of high-frequency road vibration that might otherwise reach the cyclist. The absorption of road vibration is not going to affect the speed of the cyclist but it is an endearing feature of titanium that can make a titanium frame more appealing to ride.

Titanium bicycle tubing is expensive and titanium frame construction methods are also expensive. Titanium bicycle frames must be welded in an environment cleaner than a surgical operating room, free of all oxygen, hydrogen, nitrogen and carbon. Titanium welding equipment is expensive and titanium tubing preparation techniques are expensive. Immediately prior to welding, the surface of the titanium tubing must be treated in expensive ultrasonic baths.

Even the machine tools used to cut and shape the titanium frame parts are expensive. Titanium has the ability to rapidly consume cutting tools and titanium requires tools to be held in extremely stable and accurate machines that are very heavy and expensive.

Given the inherent prerequisite expenses involved in the correct construction of a quality titanium bicycle frame, potential purchasers should be wary of titanium frames that are offered for sale at unusually low prices.

A titanium bicycle frame weldor requires a great amount of skill, training and nerves of steel. One small error can send an expensive partially-completed titanium frame straight to the recycle bin. The motor skills necessary for welding a bicycle could be compared to flying a helicopter forward one millimeter off the ground at night while threading a needle with the other hand. The weldor must have a steady hand and accurate depth perception. Several tasks must be undertaken with simultaneous coordinated and absolute precision to guide a tiny white-hot pool of molten metal around various three-dimensional curves, many of which are in confined areas.

Some bicycle frame weldors have brought the cosmetic appearance of the titanium weld-bead to a high art form. Their welding is a testament to the technological beauty that can arise when man and thin metal tubing meet in the superplastic flow of hot titanium. To the extent that the undulations in filler metal do not cause stress-risers, the welds do not need to be so beautiful but it is a nice touch on a bicycle, which is itself an object of stunning technological beauty. It is only important that the integrity of the weld is sound, despite what the surface shape may look like. Weld integrity is what sets one titanium bicycle framebuilder apart from another.

A careful titanium weldor will pay meticulous attention to the preparation and application of the titanium weld to make sure that no contaminants are allowed to compromise the integrity of the weld. A careful weldor will also make sure that the frame parts are perfectly dimensioned before welding. Perfect finishing of the tube miter and careful planning of the weld sequence will ensure frame strength and alignment without cold-setting. Titanium should not be aligned to correct welding errors so the frame must be built straight in the first place (see Frame Alignment ).

The quality and strength of a titanium bicycle frame will be invisible. The purchaser must rely on the integrity of the manufacturer to supply a well-made titanium frame. Often, the quality is left up to individual employees so it is possible to find very small framebuilders who adhere to very high quality standards. Some of the finest frames are supplied by the smallest framebuilding shops.

Is Titanium Worth the Price?

A titanium bicycle is cheaper than a car.

On an upright bicycle, titanium is usually more of a luxury than a necessity. Other frame materials perform nearly as well as titanium, at a lower cost. If you ride your bike a lot or you want the strength and durability of titanium for commuting, travelling and touring, the cost can be easily justified.

If you are an occasional cyclist who is considering buying a lighter titanium frame only because you think the lighter weight will make you go faster, you should save your money and spend it on things that really will make you go faster, like training. A lighter frame will not make you noticeably faster. On the other hand a titanium frame may make you want to ride further, because of its pleasant ride characteristics.

Titanium is not a necessity on a recumbent bicycle but, unlike an upright bicycle, the additional cost of titanium is more easily justified. Upright bicycle frames can substitute steel for titanium with little change in performance. Titanium tubing is so ideally suited to recumbent bicycle frames that the choice of titanium over steel is practically irresistible.

Quality upright steel bicycles frames use a lot of “butted” tubing that has thicker walls at the ends where it joins the other tubes. Recumbent bicycle frames use a lot of tubing that has a “straight gauge” constant wall thickness throughout the length of the tube. Because of the requirement for a greater amount of straight gauge tubing in a recumbent bicycle frame, as opposed to an upright bicycle frame, the recumbent frame can take greater advantage of the weight savings offered by straight gauge titanium tubing. A tandem bicycle uses a lot of tubing so the weight savings may actually be significant.

Although performance and speed may not be significantly enhanced, the lighter tandem may be easier to handle when it is being lifted up stairs or loaded onto a bicycle rack. More importantly, a stronger titanium tandem frame can be made without adding weight.

Quality titanium bicycle frames are made with “3-2.5” alloyed titanium tubing (3% aluminum, 2.5% vanadium, 94.5% titanium) from reputable tubing suppliers.

Aluminum

Aluminum has the worst fatigue endurance of the different metals commonly used in bicycle tubing. Therefore, aluminum bicycle frames are sometimes designed to be jarringly stiff in order to avoid fatigue failures and to give the aluminum frame an acceptable service life. So much material must be used that aluminum frames may not weigh less than steel ones. Aluminum is also subject to catastrophic failure, so extra material must be added to provide an adequate safety factor. Aluminum performs well on dual-suspension downhill mountain bikes where stiffness is desirable and additional weight is not a consideration.