I do emergency braking practice whenever I get time on weekend. At speed 40kms/h, I gently apply the rear brake and front brake simultaneously. The harder the front brake the lighter the rear brake. Today I notice one thing, I can stop my bike by 15.5 feet to 16 feet. But whenever I use only the front brake then I can stop the bike less than 15 feet. What is the cause of this? Can anyone narrate please.