The humble bicycle, popular since… well that’s quite a disputed date, but from the early 1800s, the ancestors of the modern-day bicycle were certainly in use. One prominent version was the Draisienne, invented in France and patented in 1818. Charles, Baron von Drais, of Sauerbrun devised a front wheel capable of being steered, added a padded saddle, and an armrest in front of the body, which assisted in exerting force against the ground. This rst invention is more like a children’s balance bike and basically increases walking speed rather than requiring any pedalling. (see image below right). The French in influence on the these machines stuck, with bicycles known as ‘velocipedes’ until around 1869, at which point the word bicycle came into common usage.
Bicycle usage is still going strong today (and even growing). From the thrifty commuter to the Tour de France, this tried and tested mode of transport is used by millions every day around the world.
It is of no surprise that there is a huge choice of bicycle technologies and designs, with their relative positives and negatives analysed in great detail on cycling forums and in magazines. Here, we will focus on the bicycle frames and what material they are made of. This choice has a dramatic effect on the way a bicycle rides, its weight, durability, and, importantly, its cost.
To people working in the metal industry, a frame claiming to be made of ‘Alloy’ seems incredibly vague, but in the cycling world ‘Alloy’ frames always mean an alloy of aluminium. These bikes tend to be light, cheap and therefore quite popular.
A cyclist may say, however, that an aluminium alloy bike is harsher to ride and doesn’t
absorb road vibrations as well as other materials. Another downside is the material’s
tendency to fatigue and fail more quickly than, say, a steel or titanium frame. The average alloy bike has a life expectancy of 4-6 years, if well used.
Some aluminium alloys commonly used in bike frames are Aluminium 2024-T4 which contains small amounts of Cr, Cu, Fe, Mg, Mn, Si, Ti and Zn; and Aluminium 6061-T6 which contains the same alloys as the 2024, but with slightly different proportions. Aluminium alloy 6061 is a medium to high strength heat-treated alloy with a higher strength than other alloys. It has very good corrosion resistance and very good weldability, although reduced strength in the weld zone. It has medium fatigue strength. It has good cold formability in the temper T4, but limited formability in T6 temper. Not suitable for very complex cross sections. Another alloy choice would be Aluminium 7075-T6, a very high strength material used for highly stressed structural parts. Some applications beyond bike frames for this particular alloy are aircraft ttings, gears and shafts, fuse parts, meter shafts and gears, missile parts, regulating valve parts, worm gears, keys, aircraft, aerospace and defence applications; and all terrain vehicle sprockets.
Steel is a classic bicycle material choice, both sturdy and long lasting. If the bike is looked after appropriately, then a steel bike can last a lifetime. If oiled and cleaned, a steel bike won’t rust with the added bene t of not fatiguing like aluminium alloys and will wear well. The obvious issue when compared to aluminium is that steel is much heavier; however, if a high grade of steel is used, this difference is lessened signi cantly. These high quality steel bikes tend to be hand-made, and this is, of course, re ected in the price. It is possible to get a bargain steel bike, but be prepared when lifting it!
Steel bike a cionados say that a steel bike offers a more comfortable ride than aluminium, so if you are looking for a pleasant journey and durability, steel may be the right choice for you. Common steel alloys in bicycles are high strength steel alloys (generally chromium- molybdenum); one of the most successful older steels was Reynolds “531”, a manganese-molybdenum alloy steel.
A US manufacturer brie y offered a frame made of beryllium tubes (bonded to aluminium lugs), but given the health worries of this material and the price ($26,000 for frame and fork), perhaps unsurprisingly, they never really caught on. Reports stated that the ride was very harsh, but the frame was also very laterally exible.
Very much a choice for racing bicycles, magnesium is a very lightweight material, offering a 34% weight saving by volume compared to aluminium. Other positive attributes of magnesium include the highest dampening rate of all structural metals and a better fatigue life. One small issue is that these bikes cost upwards of £3000. AZ61 alloy, from which some of these racing bikes are made, contains 92% magnesium.
Titanium is often seen as the perfect frame material for bicycles, whether for racing or commuting, but what exactly is it that makes this metal such a sought-after material, and why is it that in reality, it is not actually that popular?
Titanium certainly has its positives after looking at the other choices; it doesn’t rust like steel, doesn’t fatigue or give way to rumbling road vibrations like aluminium alloys; it is also strong and won’t crack like some non-metallic options, for example carbon bre.
The main problem with titanium bikes is the price. The metal itself is not that expensive, but due to its properties, it is dif cult, and therefore expensive, to cut and weld. If corners are cut during the manufacture of titanium bikes, contamination can happen, causing potentially catastrophic failure when in use.
A titanium bike is a carefully considered purchase, made by someone who is looking for quality at a high price, you are certainly looking at over £2000 for one of these bikes.
Usually, Grade 9 titanium is used for bike frames. This alloy contains 94.5% Ti, 3% aluminium and 2.5% vanadium, and is used because it combines the variety of bene ts of other grades, but with an ease of machining not seen in other similar alloys This means that it is signi cantly stronger than the ‘pure’ grades of titanium, but is easier to weld and make into something useful; essential for keeping prices down to a vaguely sensible level.
In the interest of fairness, I should also mention that carbon bre bicycles are also available, as well as frames constructed from more exotic materials, such as bamboo!