Hello Hazar
The data I have for the Peugeot 307 Hatchback (01-07) 1.6 (90) HDi E 5d, lists it as having a kerb weight of 1306Kg, and a maximum towed mass of 1360Kg which gives a towing ratio of 104%. The EU stipulates that the minimum nose load should be 4% of the trailers MPTLM which would be 55Kg. If you are using the suggested maximum towing ratio of only 85% the trailer would not be more than 1110Kg and that in turn sets a minimum nose load of 44Kg – well within the cars 60kg limit. The EU only stipulate a minimum nose load figure, so there is nothing to stop you from using a bigger value, provided it doesn’t exceed the mechanical limits of the car or the caravan chassis. The car manufacture will have taken all the loadings into account when specifying the rear suspension. Technically provided neither the tow ball limit or the boot loading margins are exceeded, the towball should settle between 350 and 420 mm (road to the centre of the ball) above the road in the towing condition. If the ball is below 350mm when hitched with no more than 60Kg nose load, then either the car is overloaded, or there is something broken or worn in the suspension.
Spring assistors are not necessary, and it certainly does not increase the car’s nose load limit. Their use will only adjust the cars ride height and they will affect the cars handling.