Harmonics are the noise and vibration created by a tyre as it rotates against a road surface.
You will often see that a tyre’s tread pattern is made up of a number of different “sections”. These sections each have a harmonic of their own and tyre manufacturers will spend a great deal of time and research in reducing them. A reduction in harmonics is usually achieved (as much as possible) by accurately aligning the design of each tread pattern section to create as quiet a tyre as possible.
A tyre with a very aggressive pattern, or perhaps a winter tyre, will by design produce more noise than a tyre designed for comfort. Again it comes back to the requirements of a particular tyre – whilst a certain degree of comfort is required for a high performance sports car, it is not of the utmost importance. Conversely, a luxury car has a very high requirement for comfort and a very aggressive – and therefore “noisy” – tread pattern will not achieve this.