The trays without the metal insert are more than strong enough for carrying bikes up to 60 lb. They have passed all of our testing protocols and have been in production for years. Given the construction of the trays, if they are impacted, they can be compromised and the user may not notice and continue to use the rack. Usually someone bumps into them or they back into something and do not notice. The metal inserts are an extra fail safe in the event a tray is impacted. ALL universal EX wheel trays come with them now. As always it is good practice to take note of your rack and tray's condition before carrying bikes on your rack.