A visiting Sydney cyclist has described how nails thrown onto Perth roads on Sunday caused "carnage" and sabotaged cyclists' bids to qualify for the UCI Gran Fondo World Series.

More than 1000 riders filled Perth's CBD and major roads on Friday and Sunday for the second qualifier event promoted under the 'Experience Extraordinary Western Australia' tourism campaign banner.

Perth will also host the World Series in September.

Craig Hobart had already made the cut in the first qualifier, held in Victoria, but like many others flew in to familiarise himself with the route for September.