Did I get this right?
if not what is the way please write it as if using a calculator. I don't understand math.

52 sprockets / 12 sprockets on the rear= 4.333 ratio? X 60rpm crank speed x (20†x pi=62.8inch circumference) = 16327.987 inch min. / 12 inch = 1360.6655ft/min. and then 5280/1360.6655 = only 3.88 mph???

 

Your error is in the last conversion.

Allways write out the units and make sure they cancel .

What you did:
5280 ft/mile/1360 ft/min Your units end up minutes/mile.

1360 ft/min *1mile/5280ft* 60min/hr= 15.45 mi/hr

 

so it should read like this?

52 sprockets / 12 sprockets on the rear= 4.333 ratio? X 60rpm crank speed x (20” x pi=62.8inch circumference) = 16327.987 inch min. / 12 inch = 1360.6655ft/min. and then 5280/1360.6655 x 60 =

 

NO.
It should read EXACTLY like my last line.

 

52 sprockets / 12 sprockets on the rear= 4.333 ratio? X 60rpm crank speed x (20†x pi=62.8inch circumference) = 16327.987 inch min. / 12 inch = 1360.6655ft/min. x 5280ft x 60min/hr= 15.45 mi/hr