Wheela

Meet Wheela, a wheel who rolls smoothly without ever skidding.

A wheel rolling without slipping does two things at once: it spins, and its centre moves forward. Because the contact point does not slide, each turn carries the centre forward exactly one circumference, 2πr. That gives a simple link between speed and spin: v = ωr. Surprisingly, the point touching the ground is momentarily at rest, while the top of the wheel moves forward at twice the centre's speed.

A bicycle wheel of radius 0.35 m moving at 5 m/s spins at ω = v/r = 5 / 0.35 ≈ 14.3 rad/s, a little over two turns per second.

Speedometers and bike computers use this link, counting wheel turns and multiplying by circumference. Static friction at the contact point is what lets wheels roll, which is why braking without skidding stops a car more effectively than locking the wheels.

Real tyres flex, so the effective radius is a bit smaller than the outer radius. On ice or in hard braking the wheel can slip, and then v = ωr no longer holds.