http://www.DiscountRamps.com/piggyback-bicycle-rack.htm

Piggyback Bicycle Rack - Easily transport up to 2 or up to 4 bicycles with the Piggyback Bicycle Rack from Rage Powersports. Specially designed grabbers keep your bicycles in place for travel and the steel frame folds for storage or swings-down for versatility. The 2-bike add-on can be taken off to transport only 2 bicycles if needed.

http://www.DiscountRamps.com