Letter: max. 10 MB / sec Read: max. 18 MB / sec I tested with a Kingston card reader (USB3), the, the bottleneck is any more than the computer to which the card reader was connected. The card reader has supplied with other cards already on 50/70 MB / sec write and read rates. The performance is a far cry from the advertised maximum read rate of 48 MB / sec. => The cards - I have two appointed each with 32 GB - go back!