Different models of GoPro cameras have different SD card class rating requirements. This article should help you figure out exactly at what class your particular microSD card is rated.
You will notice various markings on your microSD card. Specifically what you will want to look for is a number shown inside of a circle or a number shown inside of a "U". Here are two examples:
On the Lexar card you can see that there is the number 10 inside of the circle. This identifies that the card is rated at Class 10. On this same card you can also see that it has the number 1 inside of the U shape. This identifies that the card is also rated at UHS Class 1.
On the SanDisk card you can see that the card has the 1 inside of the U, indicated that the card is rated at UHS Class 1.
So what does this mean? Class 10 cards have a minimum transfer rate of 10 MB/s. UHS Class 1 cards also have a minimum transfer rate of 10 MB/s. In terms of usage, the Class 10 card is used for full HD (1080p) video recording and consecutive recording of HD stills. UHS Class 1 cards are used for real-time broadcasts and recording large HD video files. Both of these cards could work fine with any of our cameras. If a card is rated at UHS Class 1 (U1) and doesn't display the Class 10 logo, as in the SanDisk card above, it is still safe to assume that this card is supported in all of our cameras as it is at least equivalent to Class 10 cards.
For more information about microSD card class speeds, take a look here.