The latest from Garmin

The memory card class 10 is required for Garmin Driving Recorder. 

Size: between 4 GB to 32 GB max.

ClassMinimum performanceApplication
SDHC Speed Class 2.svg Class 2 MB/s SD video recording
SDHC Speed Class 4.svg Class 4 4 MB/s High-definition video (HD) recording including Full HD (from 720p to 1080p/1080i)
SDHC Speed Class 6.svg Class 6 6 MB/s
SDHC Speed Class 10.svg Class 10 10 MB/s Full HD (1080p) video recording and consecutive recording of HD stills (high-speed data bus)
UHS Class 1.png UHS Speed Class 1 (U1) 10 MB/s Real-time broadcasts and large HD video files (UHS bus)
UHS Class 3.png UHS Speed Class 3 (U3) 30 MB/s 4K video files (UHS bus)

Taken from Wikipedia: http://en.wikipedia.org/wiki/Secure_Digital