An X-ray system comprising - an X-ray source configured to generate X-ray radiation and/or an X-ray detector configured to detect X-ray radiation, - at least two guide rails (20, 21), - at least one carriage on which the X-ray source and/or the X-ray detector is mounted, the carriage comprising first guide wheels (12, 13) and second guide wheels (14, 15), and - a drive unit attached to the carriage, the drive unit comprising one or more drive wheels (32, 33) and a motor drive, the motor drive being configured to drive the one or more drive wheels (32, 33), wherein the first guide wheels (12, 13) are adjustably mounted on the carriage and configured to be moved between at least two different positions relative to the carriage such that - in a first position of the first guide wheels (12, 13) the first guide wheels (12, 13) rest on the guide rails (20, 21), while the drive wheels (32, 33) of the drive unit are in a lifted position relative to the guide rails (32, 33) in which the drive wheels (32, 33) do not engage with the guide rails (20, 21), whereby the carriage is moveably mounted on the guide rails (20, 21) via the first and second guide wheels, and - in a second position of the first guide wheels (12, 13) the first guide wheels (12, 13) disengage from the guide rails (20, 21), while the drive wheels (32, 33) of the drive unit engage with the guide rails (20, 21) to form a frictional connection with the guide rails (20. 21), whereby the carriage is moveably mounted on the guide rails (20, 21) via the second guide wheels (14, 15) and the drive wheels (32, 33) which are driven by the motor drive. - an X-ray source configured to generate X-ray radiation and/or an X-ray detector configured to detect X-ray radiation, - at least two guide rails (20, 21), - at least one carriage on which the X-ray source and/or the X-ray detector is mounted, the carriage comprising first guide wheels (12, 13) and second guide wheels (14, 15), and - a drive unit attached to the carriage, the drive unit comprising one or more drive wheels (32, 33) and a motor drive, the motor drive being configured to drive the one or more drive wheels (32, 33), wherein the first guide wheels (12, 13) are adjustably mounted on the carriage and configured to be moved between at least two different positions relative to the carriage such that - in a first position of the first guide wheels (12, 13) the first guide wheels (12, 13) rest on the guide rails (20, 21), while the drive wheels (32, 33) of the drive unit are in a lifted position relative to the guide rails (32, 33) in which the drive wheels (32, 33) do not engage with the guide rails (20, 21), whereby the carriage is moveably mounted on the guide rails (20, 21) via the first and second guide wheels, and - in a second position of the first guide wheels (12, 13) the first guide wheels (12, 13) disengage from the guide rails (20, 21), while the drive wheels (32, 33) of the drive unit engage with the guide rails (20, 21) to form a frictional connection with the guide rails (20. 21), whereby the carriage is moveably mounted on the guide rails (20, 21) via the second guide wheels (14, 15) and the drive wheels (32, 33) which are driven by the motor drive.