Hi, I got a Topeak Explorer Rack with Disc Brake Mounts for my Cannondale Road Tandem 2. To get the rack to fit I had to pull the rack legs (?) apart to position them so they could be screwed into my frame above the rear axle. I assume this is because the rack is meant for a single bike. Is the pressure exerted by the rack on the frame going to cause a problem? It seems the rear wheel spins freely.