Bicycle

At the Tour de France, a cycling race, the yellow jersey worn by the overall leader wasn't a style choice — it was an ad. In 1919, the organizer made leaders instantly recognizable by picking the same yellow as the newsprint of L'Auto, the paper that sponsored the race.

For over a century, textbooks claimed bicycles stay upright thanks to the front wheel's gyroscopic effect. In 2011, Cornell researchers built a bike with counter-rotating wheels that canceled that effect out entirely — and it still balanced itself just fine.

In 1800, Paris enacted an ordinance banning women from wearing trousers. The law was technically enforced until 2013, with amendments in 1892 and 1909 allowing trousers only while holding bicycle handlebars or horse reins.