I use 120 x 90 16"Michelin city grip motorcycle tyres Inflated to 40 psi Using 4mm thick heavy-duty 325/350 16 Motocross tubes On my fido M1 (original 20x4 crap tyres) Each 10 psi saves 70-90 watts @ 48v 🤠👍 So you're 20x3 I would go for 75 x 75 -90 16" motorcycle tyres