Some of the tyre characteristics that intrude into the passenger cabin of the modern car are tyre harshness, whine, slap, and sizzle.
Harshness can be felt as a vibration or buzzing transmitted through the steel box that is the car, that makes the radio grille buzz, the cigarette lighter tray get excited, and generally is intrusive.
Whine is not “Are we there yet?, but a noise which goes up the scale as the speed rises and falls. Lug tyres on four wheel drives are prone to it. With some, you don’t need a speedo to tell you how fast you’re going.
Slap is the noise generated when the tyre is running over the joins in a concrete road.
The last one, sizzle, is the most interesting. It can be heard on a smooth wet road, or on a hot dry smooth road. It is generated by a tread pattern that has been cut up into “a lot” of small discrete tread blocks, or ribs which have lots of slots cut into them. These slots are called “sipes”, and in many cases, are placed profusely in the centre of a rib around the tyre. This is called a “highly siped pattern”. In most cases, the sipe depth is not as deep as the tread groove which separates the tread into blocks or ribs. When the tyre is half worn or thereabouts, in many cases, they disappear, so their effect on wet road holding can be described as transitory.
Sizzle can be quite annoying. Fortunately, most roads in Australia are laid with sharp screenings pressed into the asphalt, which generates another tyre noise called “coarse chip roar”, which everyone has experienced at some time. That can really make things buzz inside the car.
One particular tyre maker once released a very highly siped pattern with 3200 sipes, which sizzled. It became the subject of some criticism, which was quelled by an advertising campaign that promoted it as “ the sound of safety”. All those little knife edges wiping the road dry when it was raining were working for your safety. On a hot smooth road, bad luck!