Don't go too light or you will not be able to keep the wheel on the ground. I've had several Airheads with Ural sidecars and I'm pleased with that combination. I had a sputkin cargo hack on my R80 and it was almost too light. If you thought right turn the chair would fly.
'78 BMW R100/Ural sidecar, '99 Ural Patrol
'03 BMW R1200CLC Solo & Ural sidecar Rig
'06 Honda Big Ruckus Solo & Sidecar Rig,
'08 Ural Retro, '10 Ural ST Solo