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The 1521 advantages are longevity, rotor friendliness, low dust and quieter than either Hawk compounds. The AX6 is better than both compounds but, you will have some noise and dust. The 1521 and AX6 will allow you to modulate the brakes giving you better control of the car with out locking the wheels. Hawk tends to act like a on/off switch that will upset the balance of the car.
The Carbotech™ 1521™ is our high performance street compound. The 1521™ compound is known for its release and modulation, along with unmatched rotor friendliness. 1521™ is also a very low dusting and low noise compound with an excellent initial bite. This compound's excellent linear torque production provides incredible braking force without ABS intervention. Carbotech™ 1521™ operating range starts out at ambient and goes up to 800°F (426°C+). 1521™ is suitable for ALL street cars, perfect for your tow vehicle or fleet vehicle. Carbotech™ 1521™ is NOT recommended for ANY track use.
The AX6™ is specifically engineered for Autocross applications. A high torque brake compound delivering reliable and consistent performance over a very wide operating temperature range of 50°F to 1100°F + (10°C to 593°C+). The advanced compound matrix provides an excellent initial bite, high coefficient of friction at lower temperatures along with very progressive brake modulation and release characteristics. AX6™ offers high fade resistance, rotor friendliness at all temperatures and excellent cold stopping power. As a result, AX6™ is an excellent choice for Autocross and has gained tremendous popularity with SCCA Prosolo/Solo2 competitors for its outstanding all around performance. Many drivers use the AX6™ for street driving as well, even though Carbotech™ doesn't recommend street driving with AX6™ due to possible elevated levels of dust and noise.