The typical F-150 is about 2000 lbs lighter. After a quick glance, it looks like the standard tires for the Rivian aren't as heavy duty as most truck tires. (I suspect Rivian wants a more comfortable ride vis-a-vis a standard work truck)
Modern Dodge Ram with the Cummins is 7000 lbs. But a one ton truck is also going to have a much higher payload rating. Therefore, it's going to have tires with a higher load rating, not to mention more sidewall that will cushion road imperfections.