A series of dirt races. As you progress and level up in the "Dirt Racing Series" more tracks will be unlocked. The final track "The Gauntlet" will be unlocked when you reach 8th tier.
Vehicles that can be unlocked after reaching the following tiers:
Tier 1 - Ambleside ScrambleTier 1 - Tarn Hows ScrambleTier 2 - Derwentwater TrailTier 3 - Cotswolds Road Rally TrailTier 3 - Lakehurst Forest TrailTier 3 - White Horse Hill TrailTier 4 - Astmoor Rally TrailTier 4 - Bamburgh Pinewood TrailTier 4 - Highland Farm ScrambleTier 5 - Glen Rannoch TrailTier 5 - Greendale Foothills ScrambleTier 5 - Mortimer Gardens ScrambleTier 6 - Holyrood Park TrailTier 6 - Moorhead Rally TrailTier 6 - Mudkickers' 4x4 ScrambleTier 7 - Ashbrook Loop ScrambleTier 7 - Broadway Village ScrambleTier 7 - Derwent Reservoir TrailTier 7 - Lakehurst Woodland ScrambleTier 8 - The Gauntlet