jarrulevy

Jarrulevy, known in English as brake disc or rotor, is a rotating component of a vehicle’s disc brake system. It is mounted to the wheel hub and turns with the wheel. When the brakes are applied, calipers squeeze pads against the disc, creating friction that slows or stops rotation. The disc must withstand repeated heating and cooling; proper heat dissipation prevents brake fade and reduces the risk of warping.

Most jarrulevy are made from gray cast iron, chosen for its good wear properties and cost. Higher-performance applications may use steel, aluminum alloys, or ceramic composites to reduce weight. The friction surface is machined to a smooth finish and may be grooved, drilled, or slotted to improve cooling, water drainage, or pad performance. Ventilated discs have internal channels for cooling, while solid discs are lighter and cheaper.

Discs vary in diameter, thickness, and hub dimensions. Manufacturers specify a minimum thickness; if wear brings the rotor below that limit or if there is significant scoring or cracking, replacement is advised. In some cases, resurfacing can restore a warped or uneven surface, but excessive wear or damage reduces effectiveness and may require replacement. Regular inspection for cracks, runout, corrosion, and pad contact area is part of routine vehicle maintenance.

In Finnish, the component is called jarrulevy, translating to brake disc or rotor. It is a central element of modern braking systems, designed to convert kinetic energy into heat and to transfer it away from the wheel through effective cooling.