The 606 comes in a 90/90-21 front and a 130/90-17 rear. They have really stiff sidewalls being a DOT tyre and can be a handfull to mount, long levers and a few cold ones help. I just did a 60km ride through deep sand mixed with limestone cap rock, 15 front and 18 rear kept the bike heading in the right direction with no rim damage or pinch flats ( increasing the pre-load also helped in the deep stuff )