Steel

Twenty years ago, virtually every bike was made out of steel in one form or another. Ten years ago, there were still more steel bikes being sold than aluminium, carbon fibre or titanium put together. In the twenty-first century, things are a bit different. Why?

The good things about steel are that its easy for a frame builder to work with, it has great strength and good absorption qualities. The problems start when you want to build a lightweight steel frame. As less metal is used, the frame loses its strength and rigidity. As a result, a lightweight steel frame can have a shorter life, but more significantly will flex a great deal under pressure, losing valuable power from the rider. In addition, this effect increases as the frame ages: weve all heard a story of how Mr Smith has a fantastic old frame built out of 531 by Joe Fishface in 1960 thats still going strong... it may indeed still be going, but it will categorically not feel the same as it did the day Joe Fishface finished his welding. The flex increases with age. And, of course, we all know that steel can rust.

Where weight is not an issue, steel remains a great choice, ie, for fully laden touring bikes. It will last well, it will be comfortable, it can be renovated or fixed relatively easily.

There are many different forms of steel, each with its own properties, but if we were to make a generalisation we could sum up steel frames like this:

1.   Weight: relatively heavy if we want to preserve strength.

2.   Longevity: good, although stiffness tends to recede over the passage of time.

3.   Rigidity: heavier frames will be stiffer than lighter frames.

4.   Comfort: renowned for its absorption qualities.

Aluminium

Most new bikes sold today are made of aluminium. Its come on in leaps and bounds since its first forays into the main market place in the 1990s. Originally castigated for being brittle and uncomfortable, aluminium frames have developed at a pace into the new millennium.

The prime features of a good aluminium bicycle frame are low weight and high rigidity. The resulting machine is a highly responsive, fast accelerating weapon. However, problems remain. Aluminium has never been the most absorbent of bicycle materials. The introduction of carbon forks has gone a long way toward cementing aluminiums popularity: most road shock travels up from the road at about 45 degrees, depending on the riders speed. A carbon fibre fork can significantly reduce the amount of road shock transmitted to the rider, and is a vast improvement on an uncomfortable aluminium fork or a heavy steel fork. On longer rides, aluminium owners will still often complain of neck, wrist or shoulder pain, a sore lower back, or ask for three pairs of padded shorts.

Longevity is compromised, paradoxically, by the strength of aluminium. Its not very pliable, so stresses, knocks and accidents are more likely to cause a break than with other frame materials. A five-year frame guarantee is the norm, and many lightweight aluminium framesets carry a rider weight limit or an extremely curtailed warranty period, signifying a greater likelihood of frame failure.

Where comfort and/or longevity are not issues, the aluminium frame is a winner, eg., short time trials, track racing.

Again, there are numerous different aluminium tubesets available, all with slightly different capabilities, but we can draw some general conclusions:

1.   Weight: aluminium frames can be built to a very low weight, but not without compromising longevity

2.   Longevity: people who want to be riding the same bike in ten years time do not buy aluminium.

3.   Rigidity: excellent power transfer capabilities.

4.   Comfort: longer rides will be enjoyed more on other materials.

Carbon Fibre

The new kid on the block, carbon is surrounded by myth and misunderstandings. This is perfectly understandable: the youth of carbon fibre dictates that people are still finding out about it. Some of those people are frame builders... carbon frames are still changing drastically from year to year as its properties are explored, better understood and exploited. Design maturity is yet to be reached. The carbon frame you buy in ten years time will be significantly changed from those available today.

Carbon doesnt behave like a metal. Its strength and rigidity are directional. This means that a single strand of carbon fibre is as strong as can be in one direction, but no rigidity at all in another. To build anything, bike frames included, it needs to be layered up in sheets, with the fibres pointing in different directions, then bonded together.

This is why carbon fibre is the ideal material for road bike forks. A bicycle fork is a fairly straightforward piece of kit: we want it to be torsionally stiff, so we can lean the bike over in a corner without it flexing too much, but we want it to absorb shock coming up vertically from the road.

When it comes to frames, the equation is vastly more complicated. As a rider yanks on the bars, powers on the pedals and launches himself forward, numerous different directional forces ebb and flow through the frame, changing from one pedal stroke to another.

Heres a fact often overlooked by people talking about carbon frames. You will often hear carbon described as comfortable. In fact, inherently, carbon fibre has no shock absorption qualities. This comes not from the fibres themselves, but from the layers of resin - or glue, if you like  - used to form the carbon fibre tubes. The more layers of resin, the more cushioning will take place when bumps are encountered. Unfortunately, theres a downside. The resin, in comparison to the fibres, is heavy. But were about to get to the bottom of the Great Carbon Mystery... how come some people say its comfortable and some say its a hard ride? How come some carbon frames are light and some are heavy?

Answer: more resin = more comfort = more weight.

So can we say that heavier carbon frames are more comfortable than light ones? Generally speaking, yes we can.

The longevity of carbon frames has sometimes been called into question over the years. If there has been a problem, it has invariably occurred in the bonding process. Unsuitable resin or bad fits at the joining of tubes has led to 99% of failures in carbon frames. They are far better than they used to be as knowledge and experience has improved.

1.   Weight: can be made very light indeed, but often at the cost of comfort and strength.

2.   Longevity: variable.  Difficult to repair.

3.   Rigidity: Varies hugely from one design to another.

4.   Comfort: Changeable, but heavier frames tend to be more comfortable.

Titanium

We were always told that we could have comfort, but not rigidity. We could have strength, but not low weight. It was always a trade off. Weve all heard the shocking generalisations: steel is comfortable, but flexy. Aluminium has great power transfer, but will shake your teeth out. Steel will last forever, aluminium will snap when you least expect it. Aluminium is light, steel is heavy. You cant have your cake and eat it.

But you can.

The best titanium frames really can give you everything. Outrageous power transfer. Magic carpet smoothness. Unbearable lightness of being. Forever. How?

Titanium is incredibly strong, and it doesnt corrode. As long as the frame builder gets it right in the first place, and you dont go round riding into too many trees, your titanium frame ought to feel exactly the same in ten years time. Or thirty years time. Or sixty, come to that. Even if you do prang an Olde English Oak, it can be fixed without too much fuss.

But its the comfort thing that gets people scratching their heads. Titaniums flexy, isnt it? Durrrrr. No.

Its inherently absorbent, thats what catches people out. Shock prefers to travel around the outside of titanium molecules, not through the centre like it would in, say, aluminium. The path of the shock is disrupted and altered, dissipating its effects before it reaches the riders backside. So heres what you can do. You can build a titanium bike that accelerates like a dragster, but still smoothes out the road.

And because its such strong stuff, you dont need much of it. So you can make your bike unbelievably light, without compromising on the other features. Fiendish.

1.   Weight: unsurpassed

2.   Longevity: will never break

3.   Rigidity: great acceleration

4.   Comfort: if you look up plush in the dictionary, it says titanium bike.

Different types of titanium

Proprietary Titanium

There was a time when most major bike manufacturers carried a titanium frameset in their range, and many still do. Almost all of these frames are made of rolled and seamed titanium. The kind of tube that this process produces is relatively easy to work with, so it can handily be welded by the same production line as produces other frames in the manufacturers range. Unfortunately, this type of tubeset has to be made with fairly thick walls to keep its strength and rigidity high. This in turn makes the frame heavier and loses much of that unquantifiable zinginess that makes ti frames so special. What you end up with is a frame that feels very similar to a very nice steel frame. So... err... why not buy a very nice steel frame?

3/2.5Al Titanium

The tube of choice for speciality titanium frame producers is cold drawn 3/2.5 Al, or 3/2 as we say. The key part here is that its cold drawn: that means its forced into a tube shape under unbelievable pressure from a single billet of titanium. This can make it intrinsically up to 45% stronger than the usual rolled and seamed stuff. In turn, that means that we can use less of it, making the tube walls thinner, the frame lighter, and the titanium feel unmistakable.

6/4Al Titanium

The most advanced tube currently available is 6/4Al titanium. This can make a tube that is 30% stronger again, even compared to the best 3/2. However 6/4 is notoriously hard to work with, and cant be cold drawn. Its made into sheets, then formed into tubes. As these dont even have to start their life as cylindrical, 6/4 is ideal for frame designs which demand a high degree of unusual shaping.

Other Titanium

There are a few other types of tube that fall into the gaps between the aforementioned types. 3/2 and 6/4 as described above were developed for use in the US aerospace industry and is produced to an unbelievably high level of purity and quality. Eastern Europe and China produce large amounts of titanium for non-specific industrial usage, which could be described as 3/2 or 6/4, but which, as yet, dont measure up to the same standards. A good analogy would be tyre rubber. The rubber on a kids push chair wheels is similar to the rubber used to shoe a 747s landing wheels... but it aint the same.