This comes up a lot. People have a lot of queries about it and I found it a good read. The article is too long to post on here but I gave the summary and you can read the full story from the link
https://evobsession.com/ev-road-trials- ... onditions/
The Ideal World
I would be the first to admit that this is not a precise scientific study. To get something more precise I would have needed to drive on a circular test track, all on the same day, where no wind and temperature differences could affect the figures, and where speeds would be very precise and constant, and any shielding vehicle, constantly present or not.
The Real World
Obviously, driving on the motorway on three different days, there might have been some small differences in wind direction and strength and in the air temperature, but not significantly so. Also, I would have been very lucky to have found a large vehicle to drive behind from the start, and to remain behind it constantly throughout. There was a short period with no vehicle in front, at the start, and as the first vehicle I found was driving rather slower than I required, I switched to another, after a few miles.
When trying to drive without any vehicles in front, but at the same average speed as before, and having due consideration for other drivers on the road, I was not always able to do so. As these defects reduce, rather than increase any differences, I am not too concerned about them. Finally, one last problem was that on the last occasion the charger comms failed. As I did not get the usual e-mailed bill, you will have to take my word for it.