Starcross HP4 tires are designed for hardpacked, extreme "blue-groove" conditions. Starcross HP4 tires feature innovative knob patterns designed to help maximize cornering traction on hardpack. The wide 90/100-21 front Starcross® HP4 tire (as opposed to the typical 80/100-21 size) provides a larger contact patch that enhances predictability in blue groove conditions. The taller, wider front casing also provides greater air volume for absorbing hard landings. TT.