"It’s nothing to worry about. The increasing amounts of silica used in tyre rubber compounds has a tendency to build up quite a static charge as they spin along, so that line is an 'earthing strip' to discharge any current that builds up. It will be there for the life of the tyre, but it isn’t a wear indicator, those are at the bottom of selected tread grooves."
We have a bike in our road-test fleet with the same line around the rear tire. It's nothing to worry about. In fact, you should be glad it's there unless you enjoy electrical shocks. Motorcycle tires have a lot of different materials in the compound. One in particular, silica, helps the rubber heat up quickly and improves grip in cold and wet conditions. One drawback of silica is that it's a good electrical isolator. Tires with rubber compounds that use a lot of silica build up a static-electricity charge as you ride, sometimes enough to give you a light shock when you put your foot on the pavement, becoming the ground in the circuit.
According to our source from one of the major motorcycle tire manufacturers, that line around your tires is called "antenna tread." Unlike the rest of the compound that makes up the tire, this line doesn't have any silica in it, so it dissipates the static electricity as you ride rather than letting it accumulate. Antenna tread isn't new or peculiar to any one brand. All motorcycle tire manufacturers build it into—even car and truck tires have it—though it's much harder to see there because of the dense tread pattern. The visible line of antenna tread might fade or disappear over time, but meanwhile it's nothing to worry about.
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