The ST520 features stone ejectors which protects the casing from damage in the groove base. Its application specific tread compound resists cutting and chipping. It features a deeper tread depth for more traction and in-service time. Its four steel belt casing construction resists punctures, increases vehicle stability and contributes to more retread cycles. Its premium series features S-Tech Design. The ST520 has 40% more usable tread depth than many of its competitors.