A link to the press release https://yasa.com/news/yasa-smashes-own-unofficial-power-dens...
At this point why don't we get rid of the k prefix and write 59W/g?
Edit:
I was half joking, but various answers mention kW being standard for motors, kg being the SI unit for mass etc. All true, but as used here in a combined unit, which means "power density" it still would make sense IMO. It's not like the "59" tells you that it's a strong motor and hence you want kW to compare it to other motors. You can't, it's just a ratio (power to weigth). W/g just reads much nicer in my head. Or we could come up with a name, like for other units. Let's call it "fainpul" (short fp) for example :)
59 fp is a new record for electric motors!
Same reason you wouldn't use m²/s³ even though that's also technically correct.
Kilo is an SI prefix.
"The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J s, which is equal to kg m2 s−1, where the metre and the second are defined in terms of c and ∆νCs.[1]"
The base SI unit for power is the watt. The base SI unit for mass is the kilogram. Yes, this is dumb, but it's the way it is.
[1] https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochur...
Could the motor in question be shrunk down to 1kg, producing 59kW? Probably.
Could it be shrunk down to 1g? No.
No, it tells you nothing about the absolute size of the motor, but for the rest of us, the context clues are there to gain additional information. Someone else constructing something that obfuscates this with a micro-motor doesn't make this useless.
Significant figures exist for a reason. You are ignoring that here and creating precision that does not exist. The kilo-prefix absolutely communicates scale information to most readers.
Similarly it is useful to talk about household electricity consumption in terms of kWh/day, despite that also being a ratio that can reduce down.
The goal here is communication, not theoretical mathematical optimality that is actually worse in every real way.
It makes it easy to compare ratios: for example the aspect ratio of a movie (say 2.39) to my screen (2.33) and see that I can expect a good fit. My screen is a bit "more square", so there will be slivers of black borders on top and bottom.
Instead of 24" screen with a 16:9 ratio they should just be sold as 53 x 30cm.
Look at the silliness with folding displays where the difference in diagonal seems marginal until you open up a folding phone and realize that diagonals are just a silly way to measure things.
The YASA link is primary, links to test data and back story, and has more detail substance and authority.