Gravel and dirt. Rough and smooth pavement. The most durble version of the "GravelKing" series. ZSG Natural Compound - This compound has the same low rolling resistance as the premium compound. Its enhanced wear resistance makes it perfect for a long lasting training tire with an excellent ride. AX technology uses extremely narrow cord which is weaved at a super high density into the casing for lightness and flexibility. This increased density improves resistance to cuts and abrasions. PR Belt is a puncture resistant belt placed under the tread. It is lightweight and uses a strong fiber composition to achieve its puncture resistance capabilities.