The whole point of Austin 7 was that a cycle with a sidecar is a stupid and ineffective arrangement of vehicle, and that a real car does not need to be much bigger or heavier. I have heard that Austin 7 was as light as 360 kg?
Metric weights & measures don't mean a lot to me. These old cars were built in feet & inches. You probably know more about this than me & you're as capable of converting them as I am.

From the specifications I've already quoted the kerbside weight of the Austin 7 Ruby is 1358 lbs or 616 kg. The average weight of the Tourer range was 9 cwt or 457.2 kg. The 1929 - 30 RG Saloon (Fabric Bodied) was 2 cwt lighter at 355.6 kg.
The Austin 7 was the first small family car but two other British-manufactured cars are worth mentioning.
The 1928 Morris Minor (Morris

saloon comes out at 9 ft 10 in (299.7 cm) long. I can't find a weight for it.
The 1932 Ford Model Y (Ford

was slightly bigger & heavier. Length is quoted at 11 ft 9 in (358 cm) & as low as 1540 lbs (698.5 kg) kerb weight. The two-door model was the only fully-equipped car ever to be sold in Britain for just