Soma Shikoro Tires - 700c Various sizes
These are the tires to get if you stay on the road 85% to 100% of the time and the offroad riding you do is mellow and fairly hard-packed. These are the perfect balance of zippy and durable; similar to Jack Browns, but in plumper, funner sizes.
Once they're mounted they generally are two millimeters or so skinnier than what the labels say. 42s are more like 40s, 38s are more like 36s, etc. That's also dependent on rim width.
For Rivs, we recommend:
Homers and Sams - 42mm
Roadinis - 38mm
Cheviots - 42mm, although the 48mm will work too
Clems, Appas, and Atlanti - 48mm
Susie and Gus - 48mm, although it's a little narrow for these frames. The bottom bracket will be pretty low to the ground, so don't pedal around corners but of course, you never should anyway.