It's not that i makes the bike slower, it just makes the rider slower...
The airway passages of the cardiorespiratory system, which governs your breathing mechanisms, tend to narrow, making the inhalation of air more difficult. This is particularly problematic to those who are susceptible to asthma or exercise-induced bronchitis as they'll have an even greater difficulty breathing in cold air. Additionally, the bodily stores of glucose, stored as glycogen in the liver and muscles and converted to the energy component adenosine triphosphate (ATP), are depleted approximately five times more quickly in cold weather, which forces the body to switch to the conversion of body fat to ATP for its energy requirements...