Tires come in 20-28, 35 and 45mm +/- widths. I would stick with what you have (unspecified). For a bike tire any weight above #180 is heavy especially on a bent where you can't lift your weight off the seat in anticipation of a bump/hole. Also pump the rear tire up to the max or a bit above pressure at your weight. The front tire is less heavily loaded and might be thinned down a bit.
the smaller the tire the harsher the ride. though you may go faster or may not depending. going from the defaut tire to a 1.5" armaddillo gave about 2mph coasting down my test hill. thats at 120psi. going from about 65pis from to a 1 3/8" tire at 120 psi gave another 1mph. going from the 1.5 in back to a 1" not a real 1" but smaller gave me nothing. going from the 1 3/8" to a 1 1/8" gave me nothing. bot of these last just gave a harsher ride.