The main wheels have a large faired hub cap. The side of the tyre is pretty flat. I do not think the drag is significant otherwise everybody would buy Airbuses for their greater fuel efficiency- maybe they are slightly better, but there is not a lot in it. It is not a solution for a long range aircraft with a higher proportion of 460mph cruise, but for an aircraft flying 1 hour legs with a high proportion of lower speed flight, the increased drag is not largely significant compared to the engineering savings in simplicity.