If the USB flash drive capacity is larger than 32GB, Windows will reformat the flash drive using the exFAT or NTFS file system. Your car stereo or other device may not be compatible with this format and may only accept the older legacy FAT32 file system. You will need to use a third party tool in order to format large (64GB and above) flash drives to the FAT32 format as the integrated Windows formatting tool will not allow this.