The stock rear tire size for the Chieftan is the same as the GoldWing (180/60R16). I traded my GoldWing for the Chieftan and have a brand new Avon Cobra but it is a 180/70R16. I ran this size as it corrected the speedo which was about 3-5% off. Registered faster than actual speed. Has anyone tried a 70 series rear tire? If so did it fit OK?