Sidecar Tire Pressure Advice Needed

Hello all,

I have a 2000 Moto Guzzi Jackal with a Ural style sidecar that was originally installed by DMC Sidecars ( As I learned on this site ) and I found that the label on the bike calls for 42psi in the bike tires, but I found that the sidecar tire has 32psi in it. It was a bit dark, so I wasn't able to read the tire itself to see what the max psi recommended by the tire manufacturer was, but I seem to recall reading that the tire pressure on a sidecar should be a certain ratio to the other tires. Am I imagining that or are there rules to this? Any advice is greatly appreciated.

Thanks!
Sam