a+b measurement from 4.4.2021 chart. Lines should not cross each other. I used 100 km/h test speed in these tests. There is too much variation to say for sure which is the best pressure for lowest rolling resistance. Next rolling resistane tests will be done at 60 km/h speed. Maybe will get more reliable data at that speed. Although some measurements are exactly same already with this speed.
Problem is head and tailwinds in the test. They play bigger role at higher speeds. +10 km/h headwind means 2500w more resistance at 100 km/h. Around 60 km/h you can have almost have +20 km/h headwind to have same impact to results. What I don`T know at the moment how the car is programmed to drive and how the tire pressures effect the cars ecu program.
Test method:
Drive car warm (takes 20 km on current weather in my ID3 (warm is looked from idle fuel consumption rolling in neutral at 100km/h speed. Idle consumption is around 2,5 kwh. When that is reached the results has been reliable on the course.
- Set cruise to 103 km/h
- Zero on trip on start
- Fill measurement points on the route from AVG consumption display (highest or lowest values on the route in most cases)
- In the end fill data from end. 5,5km long test.
Make a U turn and repeat to Finish which is same as start to other direction.
Calculate a+b take 4% speedo error into account when comparing to old results.
In general more data points give you more reliability. If you can see data jumping for some reason you can redo that test. If you just take the end figures you are blind what has happened during the test.
I have previously tested my cars even on 400km test drives, but its not good for testing. Weather and other road conditions play much bigger role to results and just one tractor from side road can ruin whole day tests.