Nice ride


Went out on the Klein for a ride down the river Clyde then looping up to the canals and back east to home

Ride details here

Klein (with knobblies wheelset on) is set up as 32:16 so I run out of speed/cadence at about 23km/h – should have put on the slick wheels as that is 32:14 gearing and I can pedal all day at 27km/h – the route itself is ideal for a cyclocross bike or geared mountain bike (although really a spinning training route as opposed to a proper mtb route) and good for kids.

the ride on endomondo

Carron Valley destroyed my bike again


Well slight exaggeration – but my liking of this course has not improved.

this video is before they carried out work on the trails – http://www.youtube.com/watch?v=bgbGiuYFN-0

Went down the run and smacked (or more appropriately twatted)  a massive rock and heard it hit the downtube and crunch underneath. Then further down the run the rear started feeling squishy – stopped at the bottom to see sealant pissing out of a small hole …. to make matters worse it was the Racing Ralph UST tyre which just went on and which costs a fortune.

I opened the bag and got out the spare inner tube which I have been carrying for years unused to discover it was a 1.75-1.95 inner tube – oops not great for a 2.3 tyre … still in it went – pumped up the tyre and although a bit loose went for the second lap.

Changes to Carron Valley:

Top section very smooth now – taken away the singletrack wild edge it used to have – the one drop (kelpies staircase) they did have is now very tame. Pipeline however is great – new little prejump sections which get you up higher so yo can land on the downslope …. I lacked the balls, youth, suspension and deathwish to do some of them – but the second run was nicer so i am sure 4 in a row would be great.

A day and a walk up little Ben A’an


A snatch of the 5 year old away from school for the day, an old neighbour who is a sprightly 79 yo – a 54 yo mother-in-law and a 3 year old daughter all walked up the hill.

Riding Glen Tanar and Garmin Edge Review


Started the morning towing my 5 year old around Glen Tanar estate on her tag-a-long doing a quick 10km ride. She loves it and said she was desperate to be on her littlebike riding the trails by herself which is always a good sign.

Went for a 25km ride in the afternoon from a friend’s place in deeside over the hills and dropped into Glen Tanar estate for a quick loop. One of those rides that is mainly all up then al down and the down was mainly very smooth forestry road – not terrible exciting as no singletrack.

Next day did the same route but headed up toward mount Kean (one ofthe few Munroe that is easy to cycle) but had time pressure as I had to be back for a 4th birthday party. Will do the complete ride one day – looks promising and a good 1500m+ of climbing.

Used the new (to me) garmin edge 305 and it is brilliant – everything you would really want from a HRM / cycle computer.

Still playing around with the setup – managed to dislodge it once as i grabbed bike stem while opening farmers gate – it flew off but undamaged.

As for screen options – still playing around with setup – at the moment I have

SCREEN 1 (display 5)
Speed
Max Speed / Distance
Time (cycling) / Heart Rate

SCREEN 2 (display 5 again)
Heart Rate
Total Ascent / Cadence
Calories / Time of Day

SCREEN 3

map

SCREEN 4

altimeter graph

Casio G-Shock Frogman


SO Expensive on the internet - even in their sale

Throwaway from bored pal – frogman from Iraq duty free – seems well made just not so sure on the size.

What

the back shot through the strap

20

G-SHOCK 25周年記念マーク

[translated from Japanese]

Since its debut in 1983, 25th anniversary G-SHOCK evolving from the 5th Anniversary Limited Edition 25 “Guroriasugorudo” appeared.
An assessment of the 25th anniversary finally has featured throughout the series with a limited commemorative gold. Beauty lock buttons, screws, metal parts, such as gold back cover all uses IP. Use the dial is black, printing and liquid crystal glass, gold printed dial combination, and interface design firm. Bezel, band, means a new start for the 25th anniversary of evolution following his departure from the neutral image of a skeleton adopt zero-cleared. Irukakujiramoderu first adopted in 1996, is also a movement that caused the great colors, G-SHOCK are also part of the history of representation. The base model has evolved origin GW-M5600, G-SHOCK clear skeleton first adopted DW-6900, solar frogman model boasted a huge hit on 3-GW-200 model lineup. The back cover is stamped into the silver anniversary is a special model of the fifth.

Casio GW-225E-7D
27,000 yen (without tax) about $290…..
Resin Band
Shock structure (resist shock)
Screw back
ISO compliant submersible waterproof 200m
Tough Solar (mass solar charge system)
Diving capability (dive time: 23 hours 59 minutes 59 seconds measurement range, a second display unit, interval time: 23 hours 59 minutes measuring range (59 seconds) 1 minute per view)
Log data (start time diving, dive time), a single memory
Site Features: Time display in 10 cities around the world diving preset, change-registration area with daylight saving time setting function
ID Function: C CARD, PASSPORT, BLOOD TYPE (Rh type / ABO type) one by one for each memory
Stopwatch (1 / 100 second, 24 in total, with a split.)
Timer (in the set: a second set maximum: 24 hours, 1 / 10, measured in seconds, auto repeat)
Alarm newsletter three times
Battery indicator display
Power saving (energy saving in the dark and turn off the display after a certain time)
Full automatic
Switchable 12/24 hour display
Low tolerance specifications (-20 ℃)
EL Backlight (full auto EL light with afterglow function)
Monthly deviation: ± 15 seconds
Without any drive time from when fully charged solar
features when used: about five months
when power saving states: 10 months* are preset diving
Cayman (the Caribbean),
Galapagos (eastern Pacific)
Great Barrier Reef (coral reef northeast Australia)
Guam (Western Pacific),
Hawaii (Central Pacific),
Japan (western Pacific),
Mauritius (Western Indian Ocean)
Maldives (North Indian Ocean),
Red Sea,
Tahiti (South Pacific)

FBI 5km Race Day


19m47s

Race Day:

Wasn’t feeling too hot this morning as I woke up wolfed down a Clif Bar then went to staging area.

Race was quite busy and about 400 runners maybe. Started near fron then legged it the first km (for me) to get a bit clearer. Think there were about 15 people ahead of me but gradually started to edge back overtaking 4 or 5 then having 1 overtake me.

Ran past my lodging and on another day I would have been tempted to call it quits there – but today was good – didn’t drink last night and I think I was even in bed by 11pm.

Finished got my T-shirt, and then cheered the other 3 from work as they came in.

Pretty happy as it is my best 5km result (err out of two run – so it was always going to be my best or worst)

British Top Cycling Cities


When  Cycling Plus ran an article ranking Britain’s 20 biggest cities for cycle-friendliness some thought it would get people talking, but we weren’t expecting it to make headlines across the UK.

The story was picked up by the BBC, The GuardianDaily MirrorBelfast Telegraph,Yorkshire Evening Post and Bradford Telegraph Argus, as well as countless online bloggers and forum posters.

To compile the league table, the UK’s 20 biggest cities were judged against several criteria, including:

  • Number of cycling club members (British Cycling or CTC affiliated)
  • Percentage of cycle commuters
  • Number of Cyclescheme (biggest providers of tax-free bikes through the Government’s Cycle to Work scheme) members
  • Levels of asthma-causing PM10 diesel fumes
  • Likelihood of rain/snow/sleet (ahem Glasgow)
  • Extent of traffic-free greenways and National Cycle Network routes
  • Number of independent bike shops
  • Annual cycling casualties
  • Bicycle theft levels
  • Road quality

Bristol, the country’s first official Cycling City, came out on top, largely because its residents are more likely to be found riding bikes than in any other major urban area in the UK. It has a dedicated population of sportive riders, club members (one in every 267 residents has joined CTC – a total of 1,426) and cycle commuters (4.94 percent of Bristolians get to work by bike, and one in 86 has got a subsidised bike through Cyclescheme). Good weather was also in the city’s favour.

However, the news wasn’t all good, with concerns over traffic and unspent central government funding, and high levels of bike theft a particular problem. Andrew Piper of Bristol cycle shop Psyclewerx said: “People get followed back from cycle tracks and even the main roads. I tell customers to drive in a loop a few times before heading home if they’ve got their bikes in the back of their cars, and to stop and look around them at a quiet junction as they’re approaching their street to see if they’re being followed.”

The final ranking was:

  1. Bristol
  2. Nottingham
  3. Leicester
  4. Manchester
  5. Edinburgh
  6. Newcastle
  7. Stoke-On-Trent
  8. Cardiff
  9. Swansea
  10. Plymouth
  11. Coventry
  12. Belfast
  13. Liverpool
  14. Hull
  15. Leeds
  16. Sheffield
  17. London
  18. Glasgow
  19. Birmingham
  20. Bradford

Comments on internet forums ranged from “Bristol? They must not have stayed overnight or they wouldn’t have had a bike come morning” – to “Deciding which UK city is best for cycling is a bit like deciding which one of Jedward (or Kriss Kross for US readers) is the more talented”

Today’s run: training for the 5km still


Yesterday was all about putting in the miles …. slower run for twice the time that the 5km race will take.

Today is tempo running:

It’s all about versatile race-pace efficiency. It is a bit like long interval runs although the tempos are run at close to race pace as opposed to muck quicker and unsustainable pace. (unsustainable for longer than a minute)

So later on it’s going to be this:

  • 2x 10 minute, with 2 min recovery jog
  • 2 x 15 minute, with 3 min recovery jog

ANOTHER OPTION (on track)

20 x 400m runs (5k effort) with 100m jog in between.

After today I have mini fartleks on wednesday then taper off for Saturday race day.

Here is the data – struggled in the heat so did 10min quicker 1.5m slow 10min quick 3m slow 15km quicker …. then I popped into gym and did 15min on the bike (in glorious air-com)

What your bike is made of: Part 6 something else


Scandium:

Scandium is number 21 on the periodic table of elements. It was discovered over 120 years ago but gained importance during the Cold War, when Soviet scientists and engineers began experimenting with it as an aluminum alloying element. They discovered that it allowed them to weld high-strength aluminum alloys they previously could not.

In the bicycle world, Scandium refers to frame tubing made from an aluminum alloy that includes the element Scandium. In most cases, the tubing base is a high-strength, 7000-series aluminum alloy. The addition of Scandium allows the stronger, non-weldable base aluminum alloy to be welded. Previously, these and similar base alloys could only be made into a frame by bonding them together using high-strength adhesives and cast or machined lugs–almost like high-tech tinker toys.

Compared to standard 7000 series aluminum, the addition of scandium gives this new alloy the following added benefits:
• Improved strength
• Better fatigue and failure properties
• Enhanced weld strength

Scandium opens up new opportunities for frame engineers. In the past, aluminum tubing required larger diameter tubes to achieve the strength necessary to support riding. The larger diameter tubes resulted in stiff ride characteristics, which are fine for time trials but less than ideal for century rides. With Scandium tubing, frame engineers are able to use smaller diameter tubes, thinner cross sections, and shaped tubes to tune the ride characteristics of each frame while using less material. This results in comfortable, efficient, and light frames.

Scandium frame tubing also has increased fatigue life and improved failure modes when compared to traditional aluminum frame tubing. These added benefits come as a result of the same complex metallurgical reasons Scandium allows non-weldable alloys to be welded.

calfee bamboo bike

Bamboo

It is appropriate for everyday use and for racing. The vibration damping is a performance advantage on longer rides. Each frame is built to order and every frame is a unique. Tubes are selected for the weight of the rider. The geometry of the frame can be any of our usual geometries: Pro, Tri or Cross. Custom frames can also be made. Mountain Bike frames are now available.

  • Details. The bike is made from Bamboo that has been smoked and heat treated to prevent splitting. Lugs are made of hemp fiber, for the all-natural look. The chainstays are available in carbon fiber for extra stiffness in the drivetrain.
  • Finish. We coat the bamboo with a satin polyurethane to seal it up.
  • Awards. Calfee Bamboo bikes have won awards for Best Road Bike, Best Off-Road Bike and Peoples’ Choice Award at the North American Handmade Bicycle Show.
  • A Calfee Bamboo bike won 1st place in the open class at the Great Western Bicycle Rally’s Concourse d’Elegance show.
  • If there were an award for “Bicycle with lowest carbon footprint” (least amount of carbon dioxide emissions in the production of the frame), this frame would win, hands down.

Bamboo Bike Features:

  • Amazing Vibration Damping – Even better than Carbon fiber!
  • High performance frame. Weighs from 4 to 6 pounds but has good stiffness. (this doesnt seem very light to me)

Bicycle frame made of bamboo (1896)

Magnesium (from Wiki)

A handful of bicycle frames are made from magnesium which has around 64% the density of aluminum. In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that was die cast in one piece and composed of I beams rather than tubes. A company, Kirk Precision Ltd, was established in Britain to manufacture both road bike and mountain bike frames with this technology. However, despite some early commercial success, there were problems with reliability and manufacture stopped in 1992.The small number of modern magnesium frames in production are constructed conventionally using tubes.

Reportedly, a major problem with these frames is corrosion caused by the chemical reactivity of magnesium. Unless care is taken during assembly of the bicycle, there is likely to be galvanic corrosion at points where steel or aluminum components attach to the frame

Interval Running in the heat of the desert


I am entering a 5km race which is starting Saturday 10th at 7am ….. not sure that is early enough as already the temperature will be 27 degrees C …. still will be fun to do a short race. Popped in a  shop yesterday morning and there was a a running magazine with an article on running your fastest 5k (with a training plan)

But a 4 week training plan so nothing to get excited about as there are only 7 days until the race but a great article. Feeling inspired yesterday a 4pm I went for a run – wow SCORCHIO still over 30 degrees I reckon and I was on an interval session. At the end my hrm had been peaking and my face resembled a slapped baby’s arse (although an ugly one with pulsing veins perhaps)

A 15min cold shower made me feel slightly human again.

Uploaded info from the Garmin 405 and even though the sprints weren’t that quick my HR was high. Need to find a graph showing HRM rates and how affected by temp.

Exported the .gpx file to SportyPal as well to see that website. Different and quite good although the NEW Garmin Training Website has just been improved as well. Here are the two examples … obviously Sportypal doesn’t do heart rate.

GARMIN (I had to split screen)

Sportypal for same run

What your bike is made of: part 5 Carbon Fibre


Carbon Fiber feel the weave

If you’ve followed parts one through four of this series on bicycle metallurgy, you’ve learned a lot about the physical characteristics that are important to consider when designing aluminum, titanium or steel bicycle frames. This installment takes a step outside the realm of metallurgy, and looks at the use of carbon-fiber composites in bicycle frame applications.

The Wonderful World of Composites
It’s common to use the terms carbon fiber and composite interchangeably, even though all composites are not carbon fiber. For example, both plywood and concrete are composite materials. The term composite refers to combinations of materials that result in enhanced properties not provided by the materials alone (concrete is a composite of cement, sand, gravel and water; most ‘energy’ drinks are preservative sugar water and caffeine).

In scientific terms, composites are generally acknowledged as those materials in which either particles, short fibers or long fibers are dispersed in a matrix. In the case of the Duralcan metal matrix composite that is found in the Specialized M2, aluminum oxide whiskers are dispersed in a 6061 aluminum matrix; while advanced composites – the types used to build bicycles – have continuous fibers embedded into a matrix (typically epoxy).To qualify as an advanced composite, it is generally thought that the fibers are continuous, greater than 50-percent fibers by volume, and the fiber has mechanical properties superior to fiberglass. Fibers can be carbon, Kevlar (a.k.a. aramid), boron, ceramic, silicon carbide, quartz, polyethylene … and probably others that I’m not aware of.

A Simple Lexicon
Here’s a simplified explanation of how terms will be used. A fiber is a single strand of reinforcing material. A bundle of parallel continuous fibers are bound together with a glue, or matrix. A single layer of this matrix is called a ply, and multiple plies are laid up to form a laminate. The plies can be laid up in various angles to produce different characteristics of the laminate. If you’ve forgotten about the other terms used in this series – like tensile strength and elongation – re-read the first installment of this series to reacquaint yourself with those terms, because they’ll be essential to our discussion.

The Numbers Look Good
If you look at the numbers that carbon fiber can boast, your initial thought might be that it’s crazy to build a bike out of anything else. But you astute students of the School of Bicycle Geekdom already know that numbers are not the only thing to look at – you need to check out the fine print. And get this: With carbon fiber, you need to throw most of what you’ve learned out the window.

Yes, it’s true that the potential for composite frame materials is tremendous. Unfortunately, the results of some early composite bicycle-frame projects have been less than satisfactory. There are reasons for the high failure rate that composite frames have endured, but the fault is not that of the material. I know you may find this hard to believe, but sometimes even rocket scientists make mistakes. The situation is similar to what happened with titanium in the 1970s. Teledyne made some frames that failed, not because the material was bad, but because the design was bad, or the execution of the design was bad. Similar things have happened with composites, and the image of the material was once not as good as it should have been.

The common folly is for the designer to underestimate the complexity of the bicycle frame. Since carbon-fiber structures are not very fault tolerant (unlike metal structures), the design and execution plays an even more important role. And sometimes the fault is not in the design or execution of the structure – the fault may be a big rock coming in contact with the downtube. While the tube might not fail from such a large impact, the repercussions are usually hidden on the inside of the laminate, or within the laminate. Microcracks can then spread through the matrix, decreasing the ability of the fiber to transfer load. Metal tends to do a bit better in these situations – but you can make metal frames that break without warning, too.

It’s All in the Lay-Up
What I’m getting at is the fact that composite materials are very complex … more complex than metals. In addition to the material itself having greater complexity, the structures are not as straightforward as metal structures. As you have learned in this series, the designer of a metal structure has two variables: material choice and geometric configuration (like tube sizes, shapes and thicknesses). Those wacky composite guys not only get those same two variables, they also get to determine how the composite matrix is laid up. Bear in mind that two structures of identical geometric configuration, weight and composite material, but with different lay-up, could yield a completely different result. Not only is it possible for the obvious – like stiffness – to vary, but fracture stresses and failure modes could also vary tremendously. And the failure modes of composite structures are plentiful: exploding laminate, fibers pulling free from a matrix, first-ply-failure, matrix cracking, and delamination. And I thought designing a metal bike was tough….


Tensile and Compressive Strength
Let’s take a look at the physical properties that have been examined with aluminum, titanium and steel frames, and see where carbon fits in (or doesn’t fit in). The way strength is measured in the laboratory is by a tensile test. In a tensile test, we use tension to pull a sample apart until it breaks. Imagine we’re pulling on a bundle of carbon fibers, doing a tensile test. It performs very well in a tensile test – actually, it performs extremely well.

But what about the compressive behavior of carbon? Not too good by itself, kind of like a bowl of spaghetti. You need some kind of adhesive to bond the fibers together, and give the material compressive as well as tensile strength. The matrix connects this whole disorganized mess of fibers by transferring the load between the fibers and between the plies. Since the matrix and the fiber combine to make up the composite, we’ll look at them together to give comparative results.

Density and Modulus
At the risk of being accused of comparing apples and oranges, I’m going to give you some guidelines for a generic carbon fiber lay-up. Bear in mind that there are many different ways to look at this, and I’m only making a comparison for the sake of continuity in the series. The density of your laminate is in the neighborhood of 0.056 pounds per square foot, which is about 60 percent of the weight of aluminum, our previous lightweight winner. The modulus of a generic not-very-high-zoot carbon fiber is about 30 to 33 MSI, or about 10 percent higher than that of steel, previously the stiffest of the three materials we’ve looked at. So you can see we’ve got some stiff, light stuff here.

When we throw the epoxy into the mix, things start to get interesting. A well-made laminate will have 62- to 65-percent fibers by volume. The Rule of Mixtures says that the modulus is proportional to the percentage of fiber in the matrix, since virtually all of the resulting mechanical properties come from the fiber. In other words, the matrix transfers the load to the fibers. So if we start with 30 MSI modulus, with only 65 percent of the matrix contributing, we end up at about two thirds of that, or 18 to 21 MSI for our modulus. Still not too shabby: density one third of titanium, and modulus about 25 percent higher.

This modulus measurement is only in the zero-degree direction though (that’s the direction parallel to the fiber in the ply), and as we know, bicycles get varying stresses applied from varying directions. That matrix does a good job of holding together those fibers, so they don’t buckle under the combined loading. Let’s rotate the ply so that the modulus is measured perpendicular to the lay-up of the fibers. Now our modulus reads a pathetic 1.5 MSI or so, essentially giving us the modulus reading of the epoxy. Yuk! What’s worse, the modulus drops off precipitously between zero and 30 degrees, giving low results almost all the way to 90 degrees. This matters because bicycle tubes (or structures) are subjected to torsional loads as well as longitudinal ones. What’s the answer? Add layers of plies that are at different angles (often 45 degrees) to the initial zero-degree layer. The result is an overall modulus of approximately 10 to 14 MSI, still not too shabby. Again, these are generic numbers for the sake of a simplistic comparison.

What is extremely cool about the ability to lay-up a laminate, is that you can dictate the exact characteristics you want your tube or structure to have. Stiff in torsion, soft in bending. Soft in both, stiff in both. You determine the characteristics – the material doesn’t dictate them. This phenomenon is called anisotropy, and you just can’t do it with metal.

The Weak Link – Elongation
Now for the bad news: carbon’s weak link is elongation. Elongation is your safety net, but with carbon it’s low, low, low. Depending on lay-up, it’s possible to get some elongation out of carbon. For example, there is a scissoring of layers in the 45-degree plies, but in general we’re dealing with a material that doesn’t have an overabundance of ductility. Composite designs are not meant to permanently bend. And when they fail, they fail all at once, so designers build in a big safety net. This is similar to what the aluminum designers do, in order to overcome the low elongation of that material.Most manufacturers are very secretive about their lay-ups, so getting good info isn’t always easy. Reading through the Trek technical manual yields numbers for the specific modulus of that company’s lay-up, which measures the modulus divided by the density. Backing these numbers out yields an 8 MSI modulus for the Trek OCLV lay-up.

(Will careful design this is no longer an issue – the scalpel has seat stays which bend – there is no linkage there – just an ability which has been designed in)

A Brilliant Future
What’s the future of advanced composites? Their reputation is definitely on the rise. These days, most of the hideously ugly carbon projects have gone away. All the top racers win on carbon rigs – Carbon is in wheels and components. Full suspension XC rigs are running in the low 20’s and the Cannondale Flash is a very sweet 16.5lbs rig.

What your bike is made of Part 4 – Titanium


‘If your bike is a Ti bride you have a mate for life…. unless you get a younger Ti bride’

The Titanium Advantage

The Titanium Development Association calls titanium “the material of choice,” and there are a lot of people in the bike industry who would agree. This, the fourth part of our metallurgy series, is about that mysterious and expensive metal, titanium. Its reputation within the industry is excellent: light weight, super strength and fatigue life, a magical ride … and a heavy price tag, to boot. So let’s find out what the physical characteristics are that give titanium such an enviable reputation.Titanium is not as rare as you might guess – it’s actually the fourth most abundant metallic element in the earth, after aluminum, magnesium and iron. In fact, there’s a lot more titanium in the earth’s crust than there is chromium or molybdenum, two of the essential ingredients that accompany the iron used for steel bike tubing.

Density and Other Properties

As we learned last time, density is the giant feather in the property cap for aluminum. This is an area where titanium also shines, and although its density is almost double that of aluminum, it’s only 56 percent as dense as steel.

Our second property is stiffness, or Young’s modulus (E). The titanium that you find used in a majority of bicycle frames has an E of around 15 million pounds per square inch – approximately half that of steel. This means that steel and titanium are roughly comparable when it comes to the stiffness-to-weight ratio. Previously, we learned that the stiffness of a frame depends on design and the properties of the material used. The same goes for titanium – you can provide a flexible or a stiff ride, depending on execution. Because of the relationship between titanium’s high strength, low density and moderate modulus, most fabricators choose tube diameters that provide a supple, shock-absorbing ride. To push titanium down into the realm of the super light, the modulus becomes a problem, because then the frame gets too flexible. In this case, I’m talking about frames that weigh in the neighborhood of two pounds. Building ultra-light frames is not an easy task in any material … including titanium.

Ti’s Real Plus: Elongation and Tensile Strength

So titanium gets two second-place marks as compared to steel and aluminum in the first two properties we examined. But when we look at property No. 3, elongation, titanium is miles ahead of either material. This is the property that tells you how far something will bend before it breaks, a kind of safety factor for framebuilders.

Elongation numbers for titanium are often 20 to 30 percent. For comparison, typical steels can be 10 to 15 percent – the higher strength steels go down as low as 6 percent. Aluminum typically runs in the 6 to 12 percent range. Higher strength aluminums again creep into the low range of single digits, with warning bells ringing loudly. Things without much elongation are said to be brittle. Brittle frame failure is not a good thing.

The tensile strength of titanium is also excellent. The cold-worked-stress-relieved yield strength of the 3/2.5 alloy (that’s the alloy usually found in bicycle frames) is typically 100-130 KSI or more. This compares favorably with many steels we find in bicycles. Remember, too, this is achieved with fantastic elongation numbers, and at almost half the weight. And we haven’t even talked about fracture toughness and endurance limit yet.

Fatigue Strength

The fatigue strength is another property where titanium performs beautifully (By now, you may be asking: “Is he ever going to say anything bad about titanium?” ). As explained in the previous instalments, there is not a definitive measurement of fatigue strength that will tell us how the material will last in a bicycle frame. Bicycles are subjected to forces of varying amounts in a random, cyclic fashion. As long as these loads are kept below a certain level, titanium and steel both have thresholds below which they will never fail. Almost none of the aluminium (including the metal matrix composites), magnesium and beryllium used in bicycle fabrication has a defined endurance limit, so you need to design around it, as was explained last time.

Now for the Bad News….

The negative sides of titanium are several, and they will keep titanium from becoming ubiquitous in the market. First, it’s expensive. Not only is the cost of energy used to extract the metal costly, but the processing requirements are cost intensive as well.

The other problems have to do with fabrication. You’ve certainly heard that titanium is hard to weld and machine. A more accurate statement is that it is different to weld or machine. What you can’t do is cut corners with titanium. Meticulous procedure is essential. Without it, you risk contaminated welds, which can result in catastrophic failure of the weld.

If steel is “density challenged” and aluminum is “strength challenged,” then what challenges face titanium? Modulus is the biggie. Even if we start building our bikes out of higher strength titanium like 6/4, the modulus will stay the same. As the walls get thinner and the diameters larger, stiffness goes up and weight goes down – but to enter the next generation of reduced-weight framesets using conventional tubes and methods, the walls will be so thin that buckling will be a problem. There are ways around the buckling, however. Several manufacturers already have titanium bikes that have internally butted, externally butted, formed or swaged tubes, or some combination thereof. Watch for more development in this area as a way to continue exploring the limits of lightweight, strong frame design with adequate stiffness.

Will titanium be considered the metal material of choice in the future? Its position and reputation as a magical metal probably won’t be seriously challenged for a while.  Although the extremely low-price barrier probably won’t be broken, continuous improvements in tube forming and fabrication techniques as well as that legendary ride quality will keep titanium’s demand and reputation strong.

What your bike frame is made from Part 3: Aluminium (aerospace grade and the rest)


Aluminium’s  is Bright and ever so Shiny

Aluminum as a frame material has increased dramatically in popularity over the last three decades. In the early 1980s, aluminum bikes were a novelty, only available from a small, select group of high-end manufacturers. Then, in 1982, Cannondale jumped on the scene and began to push the material downmarket. Today, almost every medium-to-large manufacturer has produces the majority of their bikes in this material.

Furthermore, there’s plenty of material for them to use – aluminum is the most plentiful metal in the earth’s crust. And except for magnesium and beryllium, it’s also the lightest structural metal. A primary source of aluminum is the ore bauxite, named for the town where it was first discovered – Les-Baux-de-Provence, in France. The ore contains hydrated alumina (Al2O3*2 H2O) with impurities of iron and titanium oxides. Sounds like one-stop shopping for the bike industry’s metal requirements, eh? It’s not really, as we have better sources of titanium and iron ore.
Making Aluminum into Tubing

The actual process that changes the aluminum we find in the earth’s crust into a tube suitable for building a bike or lawn chair is complex, ugly and energy-intensive. It’s appropriate that the most important process for getting from bauxite to aluminum is called the Bayer method.  It takes more energy to produce a pound of aluminum than what’s required for steel. And although the production of recycled aluminum takes less than 5 percent of that amount of energy, virgin aluminum is needed to make wrought products – those that are rolled, extruded, or drawn.

A number of different alloys are produced using raw aluminum. For bicycle fabrication, the resultant wrought aluminum products commonly use a four-number designation system. An example of this would be the venerable 6061 alloy. Cast aluminum alloys use a three-number tag, a period, then a fourth number. Both wrought and cast alloys use another number that comes at the end: the temper designation. No doubt you’ve seen the T4 or T6 condition listed after some of the alloys: 7075 T6 or 2024 T4, for example. It describes what cold work, heat treatment and aging processes (if any) the material has been subjected to.

The tempering has a huge effect on the mechanical properties of many alloys of aluminum (some alloys are, and some aren’t, heat treatable). When you weld a 6061 downtube to a 6061 head tube on a bicycle frame, the as-welded condition will have lower strength than before it was welded. You then need to solution heat treat, and artificially age the frame, to return it to high strength. And although 7005 alloys, like the Easton Varilite, don’t need to be heat treated after welding, they do need to be artificially aged. When you age and heat treat, you’re mucking around with solid solutions; crystalline structures; the saturation of alloying constituents; their subsequent submicroscopic precipitation; and a bunch of other very small, but very significant changes that I’m not going to discuss.

Alloys that aren’t heat-treatable are often strengthened by cold work – also known as strain hardening, or work hardening. Rather than change the structure by recrystalizing it, cold working changes the structure through brute force, such as rolling, drawing, straightening or flattening the material. Examples of this type of alloy are the 5086 and 5083 alloys that currently are seeing some use in bicycle frames.

Note that when you heat treat – which really should be called thermal treatment – there are two different steps. The first is the solution heat treatment, which is usually done between 800 and 1000 degrees Fahrenheit for a number of hours. The aluminum is then quenched – in air or water, depending on the alloy – to room temperature. After that, the aluminum must be precipitation hardened (also known as aging).

The alloying elements that went into solution during the heat treatment will precipitate out over time, increasing the strength of the aluminum. Since the alloying elements are more soluble at elevated temperatures, aging is usually done in an oven (bake at 250 to 350 degrees Fahrenheit, for eight to 36 hours), so that the process happens more quickly. This is the process you hear about called artificial aging.

Aluminum’s Properties
The first property of aluminum that we’ll examine is the easiest to understand, and happens to be the one that makes aluminum so desirable as a frame material. It’s called density. Aluminum, as you know already, has approximately one-third the density of steel and nearly half that of titanium. Since our industry is so weight-saving conscious, aluminum has become a very important factor.

Consider that some of the new aluminum composites have strengths close to or matching that of CrMo, with one-third the density. But, as you good students know, we need to look at many things in combination with strength and density, so let’s do it. Even though the modulus numbers for aluminum are low compared to other common framebuilding materials, you are able to build a plenty stiff bike with it, because the low density allows you to build a bike with large-diameter tubes, without a weight penalty.

As you’ll remember from the last installment of this series, build a bike with large-diameter tubes, and the stiffness increases dramatically. And since the density is low, the walls can be thick enough to provide good buckle-resistance along with the stiffness. How stiff a frame rides is a function of its design. Kleins and Cannondales are both made of aluminum, but nobody calledthem  flexible.

The first big property challenge for aluminum is elongation. How far will aluminum bend before it breaks? Not nearly as far as titanium, and usually not approaching the limits of steel, either. If you’ve learned anything from this series, though, it’s that you have to look at a combination of factors before making a judgment.

It’s true that low elongation increases the risk of a brittle frame failure, and elongations below about 9 percent should get close scrutiny. But we need to look at strength, toughness, and the endurance limit, too.

What we find is that aluminum (except for a couple of exceptions like the 5086 alloy) doesn’t have an endurance limit. That means that even a minuscule load, if applied enough times, will eventually result in a fatigue failure. Kinda scary, don’t you think? Steel and titanium are fine in this department, aluminum is not. Clearly, there are a lot of aluminum bikes out there. Are they all going to break? No, they’re not.

How do you design around this? I posed the question to “Sir” Charles Teixeira, the Easton engineer who is responsible for the Varilite tubeset. Chuck Teixeira is a smart guy, and he knows materials. When he designs things, he pays attention to a few simple rules: One of them is to put the material where you need it. This is a very simple concept, but one that people seem to easily loose track of. The steel guys figured it out a century ago: butt the tubes.

Well-designed butts can make your frame stronger and lighter. In fact, looking at what tube sizes have worked in steel is an excellent way to determine what properties are required for other materials. This is what Teixeira did in designing the excellent Varilite tubes, which came out in 1990 and were first used for Doug Bradbury’s Manitou bikes. These were some of the first butted aluminum tubes to see wide use in the market.

Trek had been doing a bonded aluminum bike with butted tubing for a few years previous to that, but widespread use didn’t happen until the 1990’s.

The Varilite tubes have extremely thick walls in the areas of high stress, and they taper down in the areas that handle less stress. In this way, stresses are dispersed in the tube, and the life of the structure is increased. It’s not rocket science, just good design.

Optimizing Aluminum’s Advantages
To optimize the advantages of aluminum, you have to deal with its inherent disadvantages. One of the ways to accomplish this is by designing in a large margin for error. Although there are many different situations, Teixeira said that one rule of thumb he uses is to increase the tube’s static strength by about three times that of the steel bike.

A lot of factors come into play here, so this isn’t an iron- (or aluminum-) clad rule. A basic premise is that the lower the displacement (flexing), the lower the stress, resulting in less chance for fatigue. It’s also good to spread the stresses out to places of lower loading. This is the idea behind butts, lugs and gussets. Spreading the stresses down the tube also allows you to build a bike that has more resilience and a lively feel, rather than an ultimately rigid structure.

Then there’s stress corrosion, another eyebrow raiser. If you mess up that artificial aging, then stress corrosion may come back to haunt you. As you can see, we have a very complicated puzzle in front of us.

Gary Klein really pulled Aluminium up into elite racer territory – using thin wall tubes that were large for strength and shaped tubes to reduce flex.

He also ran cables through the tubes and these butts were actually found to increase stiffness and strengthen the frame. My old attitude frame weighed in 2.8lbs which was nearly half a pound lighter than anything else around at the time. I hear he got bored of bikes after Trek bought his company (and that other great indie Gary Fisher) and Klein started making telescopes. The aluminium was designated as ZR9000 which some say is just marketing speak for 7000 series which has been hydroformed.

MAKE UP:

6000 series: Al-Si-Mg. Precipitation hardenable, medium strength, readily weldable, suffers from grain boundary weakness.
7000 series: Al-Zn-Mg-Cu-Ti. Precipitation hardenable, very high strength, weldable or so, suffers from grain boundary weakness unless doped with silver.
8000 series: Al-Li, principally, but were developed from 7000 series, so may have any additions from them. Precipitation hardenable, high strength, 1%Li lowers alloy density by 3%, so lighter than most Al alloys but Li boils in the weldpool making them a b*st*rd to weld until the Russians developed new techniques. Now only a partial b*st*rd to weld.

What does the future hold?  It’s still hard to beat good old 6061, when you look at the whole package. It’s the most versatile of all alloys, has excellent toughness for an aluminum, and good elongation, too. Like the point I made last time with high-zoot CrMo versus generic CrMo, we know that you can make a good bike out of either – it’s just that it takes smart design from the tube on up to build a good bike.We’ll learn more about some of the new higher-strength aluminum alloys and associated materials in the exotics part of our series, which will come at the end, after titanium and carbon fiber.

As you may have guessed, the next installment in will cover titanium.

What your frame is made of Part 2 – STEEL (is real baby)


custom frame by Robin Mather

Steel is Real

Bicycle framebuilders have known about the secret of steel for a long time. In fact, steel has been used to build more bicycle frames than any other material. It has also been used about 50 years longer than any other material currently in use.

Steel or Fe, from the Latin ferrum – and that’s where the term ferrous comes from when we refer to ferrous and non-ferrous materials. As you may have guessed, steel is a ferrous material, and aluminum and titanium are non-ferrous.

Iron is the fourth most abundant element in the earth’s crust, so in the near future we probably won’t be running out of the material that’s used to build steel bikes (chromium and molybdenum are different stories, however). Iron rarely occurs as a chemically pure metal, except in meteorites.

How do we get from iron to steel? We add and subtract a couple of ingredients while its molten, and voilà, steel – OK the truth is more complicated but yes it does happen.

4130 steel – an alloy steel – which is commonly known in the bike industry as chrome-moly, contains the following alloying agents: 0.28- to 0.33-percent carbon, 0.4- to 0.6-percent manganese, 0.8- to 1.1-percent cromium, 0.15- to 0.25-percent molybdenum, 0.04-percent phosphorous, 0.04-percent sulfur, and 0.2- to 0.35-percent silicon. The other 95-plus percent is made up of good old-fashioned iron. Now, there are hundreds of kinds of steel, but 4130 finds its way into bike frames because, among other attributes, of its weldability, formability, strength, ductility and toughness. (Some cheap bikes are made with 1020 steel, which is called plain carbon steel, and has significantly lower strength than the chromium-molybdenum steels.)

The numbers that I’m throwing out are designated by the Society of Automotive Engineers and American Iron and Steel Institute: 41XX designates a chromium-molybdenum steel (CrMo), while 10XX designates a plain carbon steel – which, if compared to 41XX steels, has fewer alloying agents, lower strength and lower cost. The first number specifies the type of steel: 1 = plain carbon, 2 = nickel, 3 = nickel chromium, 4 = nickel, chromium and molybdenum, 5 = chromium, etcetera, ad nauseam…. The second number relates to different things with different alloys. In the case of 4130, it defines the percentage of chromium and molybdenum in the alloy. The last two numbers tell you the amount of carbon, expressed as hundredths of a percent. 4130 therefore has 0.3 percent carbon.

From now on, in the bicycle lexicon of this series, I’ll be using 4130 and CrMo interchangeably, even though not all CrMo’s are 4130. CrMo is by far the most common of all the steels used to build high- quality bicycle frames. And I’m making an assumption that the readers who ride steel frames aren’t riding crap.

look at my lovely lug

Choosing Steel as a Frame Material
The bicycle-frame designer must take many different factors into account when deciding what material to use for fabrication. Even after looking at all the characteristics, there is no clear choice.

But even so, there are many good reasons to use steel as your material of choice in a bicycle frame. Let’s go over the physical characteristics that were defined last time, and see where steel fits into the scheme of things, as compared to titanium and aluminum.

(Disclaimer: For the sake of simplicity, I will refrain from making comparisons to carbon fiber, metal matrix composites and other materials now. When those materials are covered, comparisons will be drawn to Ti, Al and steel.

Density
We started with density in the opening article because it is perhaps the easiest property to understand. Unfortunately for steel, it is “density challenged,” to use 1990s vernacular. Weighing in at 0.283 pounds per cubic inch, it’s almost twice as dense as titanium (at 0.160) and pretty near three times the density of aluminum (at 0.098). Clearly, density is a very important property, because light weight is where it’s at with bicycle frames these days, and high density makes it tough to push that weight envelope.Fortunately for steel, there are other important properties to examine.

Stiffness
This is where steel shines, as compared to Ti and Al. Young’s Modulus for steel is approximately 30 million pounds per square inch. The titanium alloy Ti3Al-2V is 15.5 million psi, and 6061 aluminum is approximately 10 million psi. Those ratios (three to two to one) are almost identical to the density ratios between these three materials. That means that the stiffness-to-weight ratios for the three materials are about the same (provided you’re looking at stiffness in tension or compression).

If you really want to know, Young’s Modulus is the ratio of stress-to-strain in the region below the proportional limit on the stress-strain curve. This was briefly described last issue. All you need to know is: the bigger the number, the stiffer the material. Wait a minute, though. How come, if steel is so stiff and Al is not so stiff, that those big-tubed aluminum bikes are so incredibly stiff? Young’s modulus measures the stiffness for all of these materials with the same-size specimen, or section. We can call the measurement section modulus. One of the pieces of the puzzle the bike designer gets to throw in is the size and wall thickness of the tubing used. Then we get to figure the polar-section modulus of the material by the formula: 0.196 (D4-d4)/D). All this formula says is that as a tube’s diameter increases (D), the stiffness increases to the third power of that number (d is the inside diameter). Comparing a one-inch tube and a two-inch tube of equal wall thickness., the fatty is going to be eight times as stiff as the little weenie tube. And the weight will only double. Now does the ride of those Kleins and Cannondales start to make sense? (and also the reason after riding my Klein I sometimes feel like I have been punched in the kidneys.       FAST = Unforgiving)

Another simple illustration of how this works is to compare two tubes of the same weight, and look at the increase in stiffness as you increase the diameter. Take a one-inch steel tube with a wall thickness of 0.049 inches. Compare that to a 1.5-inch tube with a wall thickness of 0.032 inches. They weigh the same, but the 1.5-inch tube is 1.6 times as stiff.

Your next question should be: “Why not increase the diameter of steel tubes like you do with aluminum, so that we get an even lighter bike?” This is where the “beer-can effect” comes into play. As a tube’s diameter-to -wall thickness ratio gets above 60- or 70-to-one, the tube is more likely to suffer failure due to buckling, or “beer canning.” Al and Ti, being lower density materials, allow you to have thicker, buckling-resistant walls.

Elongation
Once again, this property is an indicator of ductility. Simply, it measures how far a material will stretch before it breaks.While the previous properties – density and stiffness – don’t change significantly with alloy and heat treatment in any given material, elongation is another story. Like strength, elongation is all over the map depending on heat treatment and the nature of the alloy. Elongation is expressed as a percentage.

When tensile testing a material, it’s pulled apart and stretched until it breaks. Marks are made on the specimen, and the distance between them is measured before and after the specimen breaks. The difference is expressed as the percentage elongation. Steels used in bike tubing typically measure elongations of 9 to 15 percent. If the elongation number dips below 10 percent, I consider it a flag to take a closer look at the overall properties of the material.

Risk of brittle frame failure increases as this number decreases. In particular, you need to look into the strengths of the material – toughness and the endurance limit.

Tensile Strength: Ultimate and Yield
There is a huge variation in the measured tensile strength of different steel alloys and different brands. Generic CrMo might have a yield strength of 90 KSI, whereas True Temper OX3 measures out at almost twice as much: 169 KSI. It’s possible for a bike that’s made out of either of these materials to break. We know for a fact that straight gauge American airframe tubing is a very reliable material to build a bike with. But it has a strength of only 90 KSI. Again, maybe we’ll find that the toughness and elongation of this material is fantastic, so we can get by with a lower strength.

If the True Temper OX3 tubing is twice as strong, does that mean you can build a frame with half the wall thickness? Yes. Will it be as strong? No. Will it be as stiff? Heck no. Will is last as long? Doubt it.

The Big Picture
The point here is that there is a lot to consider. If you merely look at a couple of the numbers, you’re not necessarily getting the whole picture. It’s easy for a metallurgist to convince an ad guy about the superiority of one material over another. Look at the two materials mentioned above. Very different strength numbers, identical density, yet you can build a good bike out of either material.

Steel is a wonderfully reliable material for building bikes. It’s safe to say that there’s no more successful material ever used. It’s easy to work with, can be easily welded or brazed, requires simple tools for fabrication, fails in a predictable manner (as opposed to sudden or catastrophic), and is cheap!There have been few challengers to steel’s throne of best material in the last 100 years. For a 4 decades, we have seen aluminum increasingly being used in bikes, and titanium has been used successfully for about 30 years. But steel is being seriously challenged by an increasing array of relatively (in bike building) newer materials. To learn more about these, stay tuned….The next installment of this “Heady metal” series will cover aluminum.

What your frame is made of PART 1


This is all reaped from an old series on frame building from velonews.

The Basics

What is the best material to use in building a bicycle frame – steel, aluminum, titanium or carbon fiber? What about something even more exotic?

There are often misleading ads that our industry uses to prey on the underinformed. It really doesn’t matter that boralyn was used for tank armor, that IBM missiles were capped in titanium or that F1 designers designed your bike.

To begin, you have to understand that the traditional bicycle frame is a highly evolved mechanical structure – highly evolved as in 100 years of tinkering. Attempts are constantly made to improve on its design, but most do little improving. Just designing a better frame may look like a simple problem, but it’s not. Small improvements are made with materials, suspension and engineering advances, but improving by leaps and bounds doesn’t happen – unless you believe the ads.

Because the science of bike design is so complex, I won’t be able to cover everything that’s involved. Instead, I’ll stick to the most important ingredients in the mix, and you won’t be finding out about body-center cubic versus face-center cubic phases, or about grain boundaries or persistent slip planes. But you’ll still get plenty of pertinent information to think about.

Understanding materials’ properties is essential to understanding these materials. Unfortunately, terminology related to properties is tossed around at random – this bike is stiff; that bike has a better stiffness-to-size-of-decal-on-the-downtube ratio; this other bike is fortified with 11 essential vitamins and minerals – you’ve heard the jargon.

In this first installment, I’ll define the real terminology for you, both in the technical sense and according to what it means as related to a bicycle. For the subsequent five parts of this series, steel, titanium, aluminum, carbon fiber and “other” will be examined, in that order. You’ll draw on the wonderful knowledge learned in this introduction to enlighten you down the road apiece.

Let’s Get Right Into It
What material properties are important in choosing bicycle frame material? First, there are three types of material properties:

Physical – Density, color, electrical conductivity, magnetic permeability, and thermal expansion.

Mechanical – Elongation, fatigue limit, hardness, stiffness, shear strength, tensile strength, and toughness.

Chemical – Reactivity, corrosion resistance, electrochemical potential, irradiation resistance, resistance to acids, resistance to alkalis, and solubility.

Density and corrosion resistance are important, for obvious reasons. You won’t have much use for information on magnetic permeability and irradiation resistance. And all of the mechanical properties are very important. But what do all of these terms mean, and why are they important? I’m coming to that….

Density
We’ll start with an easy one. This is how much a material weighs for a given volume. For example, 6061 aluminum weighs 0.098 pounds per cubic inch. 4130 steel weighs 0.283 lb./in3, and 3/2.5 titanium is 0.160 lb./in3. This is an important and easy relationship to remember: Titanium is about half the density of steel, aluminum is about one-third the density of steel. Use that as a guideline, then start to look at other properties, like strength and stiffness. So you ask, why doesn’t an aluminum frame weigh one third that of a steel frame? Read this series and you’ll know the answer.

Stiffness
The measurement for stiffness is called modulus of elasticity, or Young’s modulus. This, like density, is reasonably easy to understand. If you’re “in the know,” you’ll refer to modulus rather than stiffness in your conversations with friends. Consider: “Like, dude, the pot metal on that Huffy is way stiff,” versus, “I postulate, but do not conclude unequivocally, that the modulus of the Sandspeed material is adequate for its intended application.” See how much smarter modulus makes you sound?

Young’s modulus doesn’t change with different alloys or heat treatments of the same metal. A heat-treated Prestige tube isn’t stiffer than a seamed 1020 steel tube of the same dimensions. 6061 aluminum tubes with the same diameter and wall thickness are all equally stiff. But when you start using lithium or aluminum oxide, the modulus changes – although the same material won’t change stiffness with a change in heat treatment. Can anyone name an exception to this rule?

Elongation
I know that this sounds like an exciting property, but it’s not. Elongation measures how far a material will stretch before it breaks. It’s a measure of the material’s ductility. What’s ductility? It’s the ability of a material to deform plastically without fracturing. What’s plastic deformation? It’s when a material deforms when a load is applied, and remains deformed after the load is released (i.e. “it bends”). Taffy has lots of ductility. Glass is not very ductile, and it has no elongation. Breaking like a piece of glass is not an acceptable failure mode for bikes. What you want is a material that will bend before it breaks. Yes, elongation is a very important property to evaluate when you’re looking at materials, and I’ll examine elongation with each material analyzed.

Tensile Strength
This is another extremely important property. “The more strength the better” is a good rule of thumb, but only if you keep close tabs on other properties at the same time. It’s called tensile strength because the test used to determine the bending and breaking point of the specimen is done by pulling the sample apart (applying tension).

Now, bikes don’t normally fail because tension loads are too high, so it can seem like a stupid test. But, fortunately, the test also happens to be a pretty good indicator of how the material is going to behave – tensile test results are used to indicate strength, ductility, stiffness, and proper parameters for heat treatment or processing. Besides, the compressive strength of metals tends to closely follow tensile strength.

To perform a tensile test, you grab each end of a specimen of a known cross-sectional area, and start yanking. As stress (force per unit area) increases, so does strain (a change in dimension due to stress). Plotting this stress and strain relationship will give you a curve called the load-extension curve. From this, you can determine some of the qualities mentioned above, as well as where the yield and ultimate strengths are. Yield is where you permanently stretch the material; and ultimate is the peak load it will take, usually very close to the point where it fractures.

Fatigue Strength
Guess what? This is another important property to consider but, once again, not by itself. Fatigue failure occurs by applying cyclic stress of a maximum value less than the static tensile strength of the material … until your specimen fails. This can be a cool test, because the alternating stress mimics vibrations and impacts that happen when you ride your bicycle down the long and winding road.

The fatigue strength itself is a measure of the stress at which a material fails after a specific number of cycles. What’s tough though, is designing the proper test. Again, a bicycle is a complex puzzle to consider. There is no standard test for fatigue. Another kink is that fatigue tests are done by cyclic loading of similar stress, whereas the loads you apply to your bicycle parts are uniform.

Ferrous alloys (a.k.a. steel) and titanium have a threshold below which a repeating load may be applied an infinite number of times without causing failure. This is called the fatigue limit, or endurance limit. Aluminum and magnesium don’t exhibit an endurance limit, meaning that even with a miniscule load, they will eventually fail after enough load cycles.

Toughness
This is the ability of a metal to absorb energy and deform plastically before fracturing. A tough metal is more ductile and deforms rather than fracturing in a brittle manner – particularly in the presence of stress raisers such as cracks and notches. Since a very important requirement of bicycle tubes is their ability to deform and give warning of impending failure, toughness is an important property to measure. All things considered, toughness is a dense and complex property to analyze. There are many different ways to measure, some apply to bicycle applications, some don’t. Unless toughness is an issue with a certain property, I’ll leave it alone. If it is an issue, as in the case of carbon fiber, you’ll hear about it.

The Search for Perfection
To answer the question asked at the outset of this article, none of the materials described happen to be the perfect material to use – all have their advantages and disadvantages. Comparing and designing frames out of different materials is difficult because failure modes are so different. And welding, bonding, brazing, machining and finishing these materials are all accomplished differently. But the hardest part is wading through the bollocks from the marketing guys. Keep reading this series, though, and you’ll know just enough to get yourself into trouble.