In a supermoto conversion, you’ll be switching your 18” or 19” rear wheel to 17”. You’ll need to lose a whole bunch of teeth in the rear sprocket.
MX bikes typically have 49-51 teeth, Enduro bikes 47-48. SM’s have 38-45. Street SMs like a long gear to minimize over revving in the city and allow for bursts down the highway. On a supermoto, 42-44 is best.
You may need to change the front sprocket as well from a 12T or 13T to a 14T or 15T to obtain the desired top speed or low revs at 90-100 kph.
Choose your gears wisely; it makes a difference!