What is the weight impact on speed in a bicycle trip?

Generally speaking, when we go out riding, we are afraid to take a pile of baggage, we always feel that the luggage is too heavy, it will greatly slow down the speed of riding. Is the truth so true? Look at the old riding Alee below. What do you say?.
According to my observation, cyclists often can be divided into two different camps: one is what is the party with all heavy, a light weight loss is the ultimate pursuit of the party, for example, is very popular this year Bikepacking bike off, they can be regarded as a kind of typical party equipment. As a 10w+ km, traveled to more than 30 countries of the old driver, I always think of you in the “(equipment) to decide whether a little weight too paranoid riding speed” on this matter, and therefore had an idea: by comparing the different weight, see will have much impact the riding speed.
This is the first part to discuss the weight effects in long distance riding. The experiment was done by myself, using the Bike Calculator APP to record the data:
1, fixed preconditions
Wagon
Output power (200W)
Weather condition
Traffic
wind speed
Tire pressure (set up, roll resistance is about the same)
weight
2, baggage weight (rider weight, 78kg, bicycle weight 15kg): 5kg, 6kg, 15kg, 25kg, 35kg
It is worth mentioning that the shape of the pack and the position of the suspension also add some wind resistance, so you will see that the Bikepacker all like to use a flat pack to reduce the air resistance. To ensure the objective of the experiment, I used the package hanging on both sides.
3, then, a rough result can come out
Although I think the following data is relatively simple and crude, but it also has a certain reference value:
(1) 100km Road
5kg:, 192.04mins, 31.24km/h
6kg:, 192.21mins, 31.22km/h, +10, secs (0.1%, slower)
15kg:, 193.73mins, 30.97km/h, +1, mins, 30, secs (0.9%, slower)
25kg:, 195.45mins, 30.70km/h, +3, mins (1.7%, slower)
35kg:, 197.20mins, 30.43km/h, +5, mins (2.6%, slower)
Summary: in the case of flat road, very little effect on the speed of weight, probably every 1kg increase speed is slow, a few seconds, a day off, with more than 35kg 5kg 5 minutes.