The CT90 in its classic form was an 89 cc 4-stroke air-cooled single with a four-speed transmission and a semi-automatic clutch, coupled with a 1.867:1 ratio reduction box that was manually switched into operation using a small lever under the transmission case. The cylinder was nearly horizontal in the step-through tube/stamping frame. The fork was originally a leading link suspension, replaced in 1969 with conventional telescoping-tube suspension.