Most drivers watch the tread depth indicator on a tyre and assume it tells the whole story. It does not. Tyre rubber degrades from the inside out over time, hardening and losing flexibility regardless of how much tread is left on the surface.
Six-year-old tyres on a car driven in Singapore, where the heat and humidity accelerate rubber ageing, are genuinely past their best. The wet-weather grip drops, the sidewalls lose flexibility, and the risk of a sudden failure, while not high, is no longer negligible. Most tyre makers and Audi themselves recommend replacing tyres older than six to ten years regardless of tread depth. These were at the six-year mark.
The service items are a simpler story: oil breaks down, brake fluid absorbs moisture over time, and the throttle body picks up carbon deposits. A major service at regular intervals keeps the engine clean and responsive.