side effect the filler is used to improve mechanical properties when the filler is used less than 10 parts by weight room temperature properties and damping properties may be deteriorated by contrast when it is used in an amount exceeding 50 parts by weight fatigue resistance may be deteriorated because of reduced dispersibility preferably the natural rubber may have a mooney viscosity in the range of from 40 to 80 more preferably from 50 to 70 an example of the repeating unit of the rubber includes but not limited to isoprene of the following chemical formula ch 2 u2550 c ch 3 u2014 ch u2550 ch 2 the heat resistant crosslinking agent may comprise pmp along with at least one of p900 and hts the chemical structures of pmp p900 and hts are shown below they differ in heat resistance and flexibility of chains depending on their structure in particularly pmp improves heat resistance whereas the use of p900 and hts prevents deterioration of flexibility and dynamic characteristics the vulcanization accelerator may comprise n cyclehexylbenzothiozole 2 sulfenamide hereinafter referred to as u201c cz u201d tetramethylthiuram disulfide hereinafter referred to as u201c tt u201d or a mixture thereof and is used to improve quality by reducing vulcanization time lowering vulcanization temperature and reducing the use of a vulcanization agent the activator may comprise stearic acid zinc oxide or a mixture thereof and is used to activate the vulcanization accelerator the aging inhibitor.