English: The speed of the center of a wheel is 0.9 c . The speed of the top of a wheel is 0.994 c while the speed of the bottom is always zero. This is why the top is contracted relative to the bottom (Fitzgerald contraction, a consequence of Einstein's special theory of relativity). This animation is made with the assumption that the spokes of a wheel are much more elastic than its circumference. Otherwise there could be a rupture of the spokes or of the circumference. This is not an optical image (no eye or camera). The true position of a wheel is represented, in the referential of the ground (where the speed of the bottom of a wheel is zero). In the rest frame of the center of a wheel, wheels are circular and their spokes are straight and equidistant, but their circumference is contracted and exerts a pressure on the spokes, the contraction of the circumference is a purely relativistic effect (this shows that Fitzgerald contraction is a real effect, not a kind of illusion) but not the contraction of the spokes, because their speed is perpendicular to their length, their contraction is only an effect of pressure.