Mountain Buggy’s Duet Aerotech wheels are made from a unique blend of EVA and rubber that offer the best of both worlds in functionality, ride, maneuverability and durability. Aerotech tires have a unique hollow inner, adding ‘air’ cushioning over city terrain. Only compatible with the Mountain Buggy Duet stroller. Pack of 4 aerotech tires (2 front, 2 rear) to provide a maintenance free smooth ride for your urban adventures! When using the Aerotech wheels on the Duet, you need to remove the existing axle from the frame. The axle will slide out backwards when the gray knob is rotated forward. Aerotech rear wheels will come with the axles attached and will clip in directly from each side.