A trailer includes: a chassis; a floating coupling apparatus coupled to the chassis, a portion of the floating coupling apparatus configured to move in a vertical direction relative to the chassis; a kingpin attached to the floating coupling apparatus; a displacement-sensing device positioned between an attachment portion on the chassis and an attachment portion on the floating coupling apparatus, the displacement-sensing device configured to sense a load acting on the displacement-sensing device; and a fluid system in fluid communication with the displacement-sensing device.