How a decline can rise

| 6-01-2022, 16:43 | English

It was probably special reporter Jan de Vries van de Volkskrant who introduced the concept of ‘faux plat’ to newspaper-readers in the Netherlands. De Vries defeated the Tour de France in the Pyrenees in 1954 and noted in a lively description of the events (bony loins, well-circumcised faces, winged climbers, spine-chilling descents – Wim van Est and Wout Wagtmans also participated) that above the Soulor ‘ faux flat’ sat. A regional rider was left breathless there. A year later he started talking about it again, then it was ‘faux flat’ past the Soulor. The following week it was between the Tourmalet and the Aubisque. Readers were never told what ‘faux plat’ actually was.

 



That only came when Jan Liber van The Free People treacherous ‘faux plat’ discovered in September 1961 in the Bremgarten circuit near Bern. Faux flat, Liber knew, was ‘a very gradually ascending road that one hardly notices ascending, but which eventually gets into your legs’. The Leeuwarder Courant called the treacherous pieces at Bern flat waltz. That term now sounds as if we invented it here in Holland.

Nowadays it is understood to mean a more or less long road section with a gradient of 1 to 2 percent, maybe even 2.5 percent. Such sections of course rise 1 to 2 (or 2.5) meters per 100 meters traveled, which in practice can barely escape attention. No complaints are ever made about ‘faux plat descendant’, the annoyance always affects the ‘faux plat montant’, the gentle slope upwards, although many cyclists are also lighthearted about this. A 2.4 percent slope, says one website, which feel you don’t even if you have tailwind. Only from 10 to 12 percent do slopes become ‘challenging’ and ‘significant’. Rideable slopes go above 20 percent.

Extra counteracting force

The amazing thing is that a slope of 1 percent increases the required effort considerably. An ordinary cyclist on an ordinary bicycle experiences an additional counteracting force of 1 percent of his total weight (90 kg) from such an incline, corresponding to 8.8 newtons. (For very small angles, sine and tangent are equal.) On the horizontal Road bike and cyclist together, when riding at a leisurely pace of 15 km/h, experienced a combination of rolling and air resistance of about 12 newtons. So that’s just 75 percent.

You can just as easily calculate with classical formulas that a slope of 1 percent produces as much resistance as a headwind of 2 meters per second (assumed drag coefficient 1.15 and frontal area 0.55 m).2). For a 2 percent gradient this is almost 4 m/s. It means that the effect of a false flat can indeed be canceled out by tailwind, but also that it should not be underestimated. It is small and big at the same time.

How steep can a road be without its slope being noticed? That depends entirely on its environment. Some research is done from time to time to explain a phenomenon called “slope illusion.” There are places on earth where roads that slope indisputably downwards are mistaken for roads that lead convincingly upwards. Motorists experience a lot of fun when they see their car spontaneously driving up the slope ‘in free’. In front of astonished tourists, guides let oranges roll up the mountain and water flow upwards. In 1995 this column discussed such a place near Rome (between Ariccia and Rocca di Papa) and according to Wikipedia there are now more than 170 known, you can visit it with Google Street View to get an impression. Among the most famous are Scotland’s Electric Brae, Florida’s Spook Hill and Canada’s Magnetic Hill.

Optical illusion

Locals and guides believe that the anomaly is explained by a strange action of gravity or by anomalies in the Earth’s magnetic or even electric field and they like to call the slopes Gravity Hill, Antigravity Hill, Magnetic Hill, Electric Hill and so on.

Paola Bressan and fellow psychologists from the University of Padua demonstrated in 2003 that in all cases it is an optical illusion, an optical illusion. They recreated famous situations in a gigantic diorama, within which the slope of the roads, including the decisive before and after section, could be varied at will. Sixty students were allowed to look into the box with one eye and say what they saw. If the pre- and post trajectories rose sufficiently sharply (3 percent), the middle section was easily seen as declining by 1.5 percent, while in reality it still rose by 1.5 percent. Marcel Minnaert had already described this in 1937, as he already knew that the (incorrectly) assumed position of the horizon makes a lot of difference to the judgment about the slope of a road. Japanese psychologist Akiyoshi Kitaoka found other influences in Serbia in 2015. False flat is actually everywhere, that’s the take home message.

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