Why is my Ebike slower than 20mph?

• Power on the display by holding M button for 2 sec
• Hold SET button for 2 sec to enter setting interface
• Password :0118
• Press + or - button to choose between different settings, and SET button to enter. 
• Now choose Speed Limit and press + or - button to change it to 32 (20 mph) or 45 (28 mph)
• Change Wheel Size to 28 to get accurate current speed.
• Change Unit in the same menu. You can choose Miles or Kilometer
• Now choose Save & Exit
• You are ready to enjoy the full power of the Krafty Cafe Racer