I am working on a new project. I have been using in hub motors. I want to use a chain driven motor instead. Here is the problem. The speed of the external motors are 4800 rpm The available motor drive gears are from 9 to 13 teeth The available shaft drive gears are from 32 to 89 teeth The size of the Wheel (OD) is about 20 inch. I am trying to keep the road speed down to no more than 37 mph. Is this possible in this range? Or am I going to blow well past that no matter what ratio I choose. My math isn't that good anymore.

Well. If a car has 4800 rpm and has 4:11 differential, what would be the road speed? 60??? Go from there.

Try this. a= motor RPM b= drive gear teeth c= driven gear teeth d= wheel diameter MPH= (a(b/c) * (3.14*(d/2)*(d/2)))/ 60/5280

I came up with a motor sprocket of 8 teeth with an axle socket of 54 on a 20 in wheel at 4800 rpm at 35 mph. Please check my figure.