You donât have to make the trip to Tuscon to do a perimeter ride. We have one right here in the Evergreen State: PROS! Labor Day â September 1, 2014. The Perimeter Ride of Seattleâor PROSâis a Labor Day (September 1) ride organized by the Cyclists of Greater Seattle (COGS) that literally follows the perimeter of Seattle. PROS circumscribes the city, following a counter-clockwise route from its start at Discovery Park.