There are things every cyclist seems to believe, pieces of cycling lore passed down from rider to rider through the ages like holy writ. Problem is, an awful lot of them are either completely wrong, or based on a grain of truth that’s been mangled beyond recognition. Let’s pick a few of them apart.

Aluminium frames only last five years

Yes, aluminium frames can fail; this crack was almost certainly caused by hanging a rack and bags from teh seatpost (CC BY 2.0 garycycles7|Flickr)

Or two years, or whatever. There’s a grain of fact in this one and it’s all about metal fatigue. If a piece of metal is repeatedly flexed it will eventually break, as anyone who has idly bent and unbent a paperclip knows. This happens even if you don’t flex the metal enough to permanently bend it.

This is metal fatigue, and it’s an odd phenomenon because not all metals behave the same way. If you repeatedly flex a piece of steel by a large amount, it will eventually break. But if you only flex it slightly, it won’t. The load below which a piece of steel doesn’t break from metal fatigue is called the fatigue limit.

This kind of cyclical loading and unloading is exactly what happens to bike frames, so you can design a steel frame that will essentially last forever, as long as it’s not crashed and it’s protected from corrosion. (Bike designer Brant Richards has pointed out it's not quite that simple. "To actually hit true fatigue limit stress levels frame would be very heavy indeed," he says. Nevertheless, the relationship between stress and lifespan for steel is such that you can build frames that last literally decades.)

Aluminium is different. If you repeatedly load and unload a piece of aluminium it will eventually break, however small the load. However, the smaller the load, the longer this takes.

Having more material spreads the load around, increasing lifespan, and the shape of the piece makes a difference too. That’s why aluminium frames have fat tubes, because a larger and therefore stiffer tube has a longer fatigue life.

Using these design techniques it’s possible to make an aluminium frame that will last many years, which is why there are still plenty around from the 1990s.

Steel frames go ‘dead’

You don’t hear this one as much as you did when steel was the dominant frame material. It was rubbish then and it’s rubbish now. As discussed above, a properly-designed steel frame can last forever, and that’s been obvious for decades.

How did this one get started then? A cynic might say that it’s good for bike shops to have people believe that you need to replace something you don’t, but I think there’s more to it than that.

On a new bike, everything works perfectly, and there’s a certain excitement about getting used to the differences in feel between your new and old rides. Your old bike, whatever it’s made from, feels familiar. Familiarity can easily become boredom. It’s not that an old bike feels ‘dead’ (whatever that even means) but that the unfamiliarity of a new one is exciting.

There’s one saddle height rule that works for everyone

Read half a dozen general books on cycling and you will find as many recommendations for ways to set the distance between your saddle and pedals. Saddle height nostrums will be based on your inside leg multiplied by a certain number (1.09 from pedal to saddle is common; 0.883 from bottom bracket to saddle is a suspiciously precise other); the angle of your knee; or placing your heel on the pedal with your leg straight, among others.

These methods produce a wide variety of saddle heights for any particular rider, which should ring alarm bells. Not only that, but they variously fail to take into account flexibility, shoe size and the sole-axle distance of your shoes and pedals.

At the very best these methods give you a starting point for where your saddle should be, though they can be off by quite a bit, especially the “inside leg times 1.09” rule, which tends to produce high saddle positions.

A bike fit expert will be able to help you fine tune things, though you can do this by feel as well, making small adjustments to saddle height. It’s hard to know what’s perfect, but aches and pains in hips. knees and ankles will soon tell you if something’s wrong. Carry an Allen key and make adjustments on the road, especially if you’re doing a long ride. 100Km of hills on a wrongly-adjusted bike can do damage that takes weeks to heal.

Tyres must have a tread pattern

This one’s simple. Car and motorcycle tyres have grooves in the tread to disperse water, otherwise they can aquaplane. Bicycle tyres, being much narrower, can’t aquaplane at typical bike speeds. In fact, you’d have to be doing over 200mph aquaplane a bike tyre, in which case Dave Brailsford probably wants to hear from you.

But tyre company marketing departments remain wedded to grooves, even though they can actually degrade tyre performance. That’s because the sections of rubber between the grooves can flex and squirm into them, and that increases the tyre’s rolling resistance.

It’s telling that when a tyre manufacturer wants to make a tyre for those situations where every second counts, such as a time trial, they make slicks. Look at the Continental Grand Prix Supersonic, for example, or, for a slightly less extreme example, Michelin’s new Power Competition tyres.

Carbon frames go ‘soft’

Sound familiar? It’s the modern version of ‘steel frames go dead’ and ‘aluminium frames only last five years’. And it’s almost as daft.

As long as it’s not crashed, a carbon fibre frame won’t become weaker in use. In fact, many carbon fibre frames hugely exceed standard tests for fatigue life, to the point where manufacturers get bored and turn off the testing machines.

It doesn’t seem like they get more flexible either, at least not in ways riders can tell. The first widely-available carbon frames appeared in the early 1990s, and some have been in continual use ever since. They’d be seriously floppy by now if this was a real issue.

However, while the fibres themselves are almost infinitely durable, you can imagine that the resin might degrade over time with repeated flexing. It turns out this is what happens.

Tour magazine flex-tested carbon fibre forks and found that after 100,000 cycles they became less stiff. Chuck Texiera, a senior engineer at Specialized told CyclingTips.com what happens: “The epoxy matrix will at some point start to form little cracks, and then over time it will just have the connectivity of the fibre.”

As with so many of these beliefs, there’s a disconnect between what the engineering says is happening and what a rider can actually feel. A frame might be less stiff, but Texiera doesn’t think a rider could tell.

He said: “Over really extended periods of time, you can expect the stiffness of the frame to change ever so slightly but it’s such a small number. We can measure it but I really wouldn’t think it would be perceivable.”

Rotating weight is crucial

“An ounce off the wheels is worth a pound off the frame,” goes the old saying, implying that rotating weight, especially on the wheels, is supremely important. The claim is sometimes laid out in less hyperbolic terms that weight on the wheels counts twice because when you accelerate you have to get it both spinning and moving forward.

Problem is, it’s not true. In 2001 bike engineer Kraig Willett analysed the forces on wheels and concluded:

“When evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant.”

The idea that rotating mass is important comes from the belief that wheel inertia matters, because it’s inertia that has to be overcome to accelerate a wheel. But Willett clearly demonstrates that wheel inertia doesn’t matter, so rotating weight is also relatively unimportant.

Why not? Well, you don't do much accelerating when you ride a bike, and even when you do the acceleration is relatively low, so the power expended accelerating a bike with ‘heavy’ wheels is only fractionally higher than that needed for light wheels. Overall weight matters when you’re climbing, but even that’s not as big a factor as people imagine and it’s a lot cheaper to save weight off your middle than the bike.

In fact you spend most of your time, and therefore effort, shoving the air out of the way, and that’s a far better basis for choosing wheels. The roughly tenfold difference in the effect of aerodynamics versus total mass means you’re far better off with a pair of good aero wheels than a pair of light ones.

Narrow tyres are faster

You can see where this one comes from. In cycling, smaller things are lighter and lighter things make you go faster, right? Well, no, not for tyres. Countless measurements have demonstrated beyond doubt that rolling resistance of tyres is lower if the tyres are wider, as long as the construction — carcass thickness and materials, tread rubber and depth etc — is identical.

But is that the whole story? What about weight and aerodynamics?

As discussed above, weight, even rotating weight, has a much lower effect on performance than people think, so the few grams difference between 23mm and 25mm tyres is immaterial.

We’re not aware of any detailed modelling of the aerodynamic effects of fatter tyres, but let’s have a bit of a stab at it. Aerodynamic drag arises from an object’s frontal area and its drag coefficient.

Drag coefficient depends on an object’s shape and how air flows over its surface. A very aerodynamic shape such as a smooth wing might have a drag coefficient of 0.005, while a brick’s is more like 2.0.

Multiplying the drag coefficient by the frontal area gives you the aerodynamic drag, so drag force increases as, say, a tyre gets wider.

According to CyclingPowerLab, the frontal area of a cyclist in the drops is about 0.36m². The change from 23mm to 25mm tyres adds 0.001436m², an increase of 0.4%. That’s the increase in power you’ll need to maintain any given speed. It takes 102 watts to maintain 18 miles per hour in this scenario, which increases to 102.5 watts with the fatter tyres.

According to BicycleRollingResistance.com, there’s a 0.3 watt difference in rolling resistance per tyre at this speed between 23mm and 25mm versions of Continental GP4000s II tyres at 120psi. The half-watt increase in aerodynamic drag is therefore almost exactly countered by the decrease in rolling resistance.

The problem here is that you’re not going to get the other benefit of fat tyres – a softer ride – if you keep the pressure the same. If you do reduce the pressure, then the rolling resistance goes up too, and you end up with slightly more total resistance.

With 28mm tyres it turns out you have a bit more leeway and can drop the pressure a little. At 100psi our 28mm GP4000s IIs have 0.5 watts per tyre less resistance than 23mm tyres at 120psi, and one watt more aerodynamic drag.

Narrow tyres, then, faster or slower? The answer, it turns out, is “it depends.” The total aerodynamic and rolling resistance depends on tyre size and pressure, and which is faster changes with how you fine-tune those variables.

An extra complication we haven’t mentioned yet is speed. As you go faster aerodynamic drag increases more than rolling resistance. At finishing sprint and time trial speeds, you’re almost certainly better off with narrow tyres.

If you don’t race, though, you might have noticed that we’re talking about small differences in resistance. A 28mm GP4000s II at 80psi has the same rolling resistance as a 23mm at 120psi. Does the extra watt of air resistance matter? It’s definitely not a difference you can feel (the threshold for that is 5-10 watts depending on the individual) and it’s going to make a tiny difference to your ride time even on a long ride. You might well decide the comfort is more than worth it.

Kirkpatrick Macmillan or Leonardo Davinci invented the bike

The bicycle sketch allegedly drawn by a student of Leonardo Da Vinci (Portolanero / Wikimedia Commons (link is external) (link is external) (link is external))

It’d be nice to believe the bike was invented by a Scottish blacksmith, but the evidence is very thin indeed.

The claim that Kirkpatrick Macmillan built a treadle-powered two-wheeler in 1839 didn’t emerge until after his death in 1878. A relative of Macmillan, James Johnston, made the claim in the 1890s, but was unable to produce any documentary evidence that what Macmillan had built was a two-wheeler.

The story goes that Macmillan built the first bike, but over the following years others copied the design. Cooper Gavin Dalzell was supposed to have built one in 1845, but again there is no contemporary evidence.

Treadle-drive tricycles and quadricycles were not unusual in the middle of the 19th century and it seems likely that the late-19th century recollections of velocipedes that formed the basis for Johnston’s claims were actually of three-or four-wheeled vehicles. Cycling historian David Herlihy covers the Macmillan claims extensively in his book Bicycle: The History and points out that none of the claimed accounts of Macmillan’s bike or others derived from it actually say it was a two-wheeler.

This, Herlihy points out, is remarkable, given what a novelty a two-wheeler would have been. When the French front-drive bicycles emerged in the late 1860s they were a sensation, because riders were able to travel on them without touching the ground. That Scottish newspapers of the time made no mention of this is remarkable.

“After all,” Herlihy writes, “a single French-style bicycle in the United States in 1866 led to both a clear-cut description of the article in a local newspaper and a patent application. It seems highly improbable that an arbitrary number of equally eye-catching machines could have operated in and around Scotland's largest cities—or anywhere else for that matter—for nearly thirty years without leaving the slightest paper trail.”

Herlihy doesn’t even bother to mention Leonardo da Vinci’s alleged invention of the bike. A sketch of a bicycle-like device emerged in 1974, claimed to be part of Leonardo da Vinci’s Codex Atlanticus. The sketch was attributed to Gian Giacomo Caprotti, a pupil of da Vinci, and was claimed to be a reproduction of a lost drawing of a bicycle by da Vinci himself. It was later established to be a forgery, though da Vinci’s reputation and that of literary historian Augusto Marinoni were powerful enough that it took until 1997 for the forgery to be unveiled.

According to a 1997 paper by Prof. Dr. Hans-Erhard Lessing, the Codex Atlanticus was examined by another da Vinci scholar in 1961 and the bicycle sketch was not present, though there were some geometrical doodles that the forger incorporated into the bicycle.

Lessing writes: “the bicycle sketch is definitely a recent forgery that can be dated between 1967 and 1974”.

But why would anyone forge a drawing of a bike? The short answer seems to be ‘national pride’. The bicycle was a seminal device that laid the basis for many vital technologies of the 20th century. Karl Benz’ Patent Motorwagen — the first internal combustion engined vehicle — was essentially a tricycle with an engine, with roller chains for power transmission, tension-spoked wire wheels and a tubular steel frame. The Wright brothers, who flew the first heavier-than-air plane in 1903, were bike mechanics and like Benz used bike technologies to save weight on their Flyer.

There’s a certain kudos, then, to being the country that invented the bicycle, which is why the strongest proponents of the Da Vinci drawing were Italian, Macmillan advocates were Scottish and so on. Marinoni never conceded the Da Vinci sketch was a forgery and as recently as 2009 his followers were still defending it, albeit rather incoherently.