A: 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.