I used to carry a bag of sand over each front wheel arch in a Hillman Imp (GKV 45D) - thinks… amazed I can even remember that - to stop the steering going light at speed.
Yesterday on the drive back from the petrol station (with a 20 kg bag of coal on the back seat) what an improvement in handling!!!
Yes I have had a passenger in the back but when it is your partner/wife/child/dog you tend not to approach the limits of driveability. I wonder how much more energy is required with +20kg. Mind you i could always loose some weight so I am kg neutral.