I have a +4 2009 (Dec), 11000km, 4-leaf springs, wire wheels, and:
195/60-15 at 22 psi
full tank! (this weight difference of plusminus 50kg varies the riding height considerably, 1,5-2cm!)
with spare wheel, full bumpers and luggage rack (another 20kg!)

I think we can only compare our cars if this criteria are specified. New or weared tyres give another 1 cm.

As DaveW measured, the height of running boards (in front of the rear wheels): N/S 21,5cm O/S 20,5cm (LHD!). Measurements on other points give also a difference between N/S and O/S plusminus 1cm.

As Peter (Gambalunga) measured, the rolling radius of the 195/60 R15 tyres averaged to 288 mm (the distance from the centre of the wheel nut to the floor). The height of the lower chassis rail was O/S 155 mm N/S 165 (LHD). However, this all at 22psi and a full tank (incl. Spare wheel, full bumper and luggage rack!

I am not able to asses if this is critical or not, similar to other here. But a significant difference of 1cm between N/S and O/S. If yes, I consider to go for a reshaping a retempering of the springs, instead purchasing new.

But my question is, are the measurement results (Aldermog, Gambalunga, John V6) really a reliable indication of sagging? At least we should measure at the same pressure, full tank, and correction for different tyre size as well additional equipment (spare wheel, bumper, luggage rack). I also could imagine, that a well lubricated contra rusty leafs will make a difference. A reference of a (almost) new car under the above mentioned standardised conditions would be helpful.

However, probably a reliable indicator is if the springs are marked and the wood is flattened due to regular contact, as Dave mentioned (could the shock absorber characteristic have an influence on this?). Probably Dave's riding height is now, with the 4-seater springs, higher than the original height when Bumble was new?

Does anybody know the specs for new 4-leaf springs? What should be the unloaded camber (cm height) of a new 4-leaf spring? What other specifications can/should be provided for reshaping/retempering? Height at a certain load etc.? Is there a source for such data? What is the spec for the (rear) riding height of a new car?

Thanks for comments

Peter