Aye Ian,
Those tyre pressures on the bike seem very high to my uneducated/no chair experience mind.
The Bros and Revere run 33psi front and rear solo and only increase the rear to 42psi when carrying a passenger.
The SRX monoshock with radials runs 30psi front and 34psi rear and can get twitchy (tank slappers when crossing longitudinal ridges, formed by "super single" lorry tyres, in soft tarmac. so, I am now running cross-ply pressures and it sticks like ..... to the proverbial horse blanket. Whilst with cross-plys runs 28psi front and 32psi rear, only increasing the rear to 34psi when two up.
I post a link from the "Bribike Forum" to a thread where the B44 owner asks about tyre pressures and whilst correspondents acknowledge that modern tyres are more flexible than the old varieties, 28-30psi and 32-34psi rear seems to be a concensus.
Link:
BritBike_Forum_B44_tyre_pressures_query?Also, on the Farcebook, Watsonian Squire Sidecar Owners Group, a query regarding tyre pressures for a Harley FLXH with a chair similar to yours attached, runs these pressures, in what appear to be modern round profile, white wall tyres.
"Try 35~38 on the rear as a starter.
30~33 front and 25~28 psi chair."
Bearing in mind the weight of a Harley FXLH, compared with the B'Zuki, I'd drop your front pressure by 4 psi and rear pressure by 2 psi to start off with. And see how it feels!
Also, a phone call or email to Watsonian Sidecars, might not go amiss and see what they recommend for something like an Enfield 500 outfit. Here's a link to their website, including contact details:
Watsonian-Squire_sidecars_websiteI hope this helps. Good health, Bill