The motor diameter is 70mm, so 85mm wheels will fit, but you won’t have much clearance between the ground and the motors. Then again, that’s always the case with small wheels, so decide for yourself. With my Caguama belt setup, I have around 12.5mm clearance between the ground and the belts, which seems to be fine. The motors and motor mounds will get scratched by pebbles either way.
In your case though, a 15mm difference in diameter will mean 7.5mm clearance between the motor and ground. I believe that’s small enough where your motor will be constantly pushing small pebbles and debris out of the way. Unless you live somewhere with superb quality roads, I would go for bigger wheels / a different drive train. (Still waiting for swissboards.ch to come online )
I get 24.2 mph (39kmh) in the calculator with your specs. Perhaps you forgot to change gear ratio to 1:1 ?