Some personal estimates of speed influences:

riding surface 3% (pavement only)
bike type 2% (road bikes only)
tires 1% (road tires only)
wind 30%
human motor 50% (trained vs detrained)
ambient temperature 2%
bike weight 2%
bike age 0%
quality of components such as wheels & bearings 0%

Wind can kill or boost speed, but the strongest variable is the motor.