A file with .u8 extension is an archive file used by Mario Kart Wii game. It contains hierarchical file system for the Mario themed kart racing game. Files inside the U8 archive file are compressed using the YAZ0 format and stored to disc as SZS files. These files are optimized as read-only support file with attributes limited to file name, file size, and a directory structure. U8 files can be opened with Wiimms SZS Tools.
U8 File Format - More Information
U8 files are archive files that are compressed using the YAZ0 file to make the file size smaller. U8 file system consists of a list of nodes with each node comprising of 12 bytes as shown below.
0x00=data file, 0x01=directory entry (other values never seen)
Three bytes: Offset into the string pool for the file name
File: Offset of begin of data. Directory: Index of the parent directory.
File: Size of data. Directory: Index of the first node that is not part of this directory (skip to node).
U8 file header is 32 bytes long, with all values stored as big endian values.