When I did the Manx Classic (17 years ago now...) post war Frazer Nash owners were all over it trying to work out how it beat them back in the day. Looking at the cars sat next to each other we thought the surprise at the time must have been like a Caterham being beaten by a Fiat Multipla.
The answer is the Colin Chapman quote that the "first task for good road holding is to keep the tyre in contact with the road". The sprung weight at the rear is very little indeed with the trailing arm setup and inboard drums. As well as improving the road holding, and traction, that's also a huge confidence booster to the driver in particular over poor surfaces. The Isle of Man was a good place to get a sense of that as all the track maps mark the bumps and cambers as much as the corners. The conventional track cars were being bounced out of line to a massive extent.
The Targa Florio and Mille Miglia we could understand, Le Mans less so unless the surface improved before the Jaguar era.
David
I think you mean the UNsprung weight. Regards, John