The Yakima King Cobra Upright Bike Rack firmly grips any wheel size from 20" to 29". Holds any bike, including road, mountain, women's, bmx and kids bikes. Also handles, no problem, all those bicycles with front suspension or any type of funky suspension, thru axles or disc brakes. Connects directly to either Yakima base rack round crossbars or Thule Racks square load bars. Carrier can also connect to virtually all factory installed car racks when used in combination with your choice of Yakima Universal or Horizontal Mighty Mounts (both sold separately; see accessories below). We recommended adding a Yakima lock core (not included; see accessories below) for use with the KingCobra to secure the bicycle inside the bike rack.
I needed a rack for the bikes when we use the camper. These fit all tires and keep the bikes tight. It can be a bit tough lifting the recumbents onto the roof but once they're up there, they'll be going nowhere. You load the bike onto the tray and roll it into the locking arms. My bike is a bit long to fit in the tray perfectly prior to moving it into locking position so I have to hold onto it. For a car top this should not be much of an issue. You can find them on Ebay for about $100.