Finding Your Mods Folder
MX Bikes stores your normal community mods inside your Windows Documents folder. This is different from the Steam installation directory.
Documents\PiBoSo\MX Bikes\mods
Open File Explorer
Open Windows File Explorer and select Documents.
Open PiBoSo
Open the PiBoSo folder, followed by MX Bikes.
Open Mods
Inside MX Bikes, open the mods folder.
Documents
└── PiBoSo
└── MX Bikes
└── mods
├── bikes
├── tracks
├── tyres
└── rider
Launch MX Bikes at least once. The game normally creates its Documents folders after it has been run.