In 1990 aerodynamicists were just beginning to understand that there was a lot of untapped potential for downforce creation from the underfloor despite the imposition (in 1983) of the flat-floor, which had been regulated in (together with a ban on skirts) to banish ground-effect aerodynamics. Consequently, the McLaren and Ferrari were shaped with much more emphasis on the over-body airflow, the simple, elegant lines of both cars reflecting an attempt to turn the airflow gently around the cockpit and radiators, then accelerating it with the ‘coke bottle’ profile of the bodywork as it narrowed at the rear in order to enhance the flow to the rear wing and over the top of the diffuser. The ‘coke bottle’ remains a standard feature of F1 cars to this day, but the advent of barge boards to help turn the airflow more quickly and accelerate it more aggressively means that the simple elegance of the 1990 cars around the front has been lost.
The change in emphasis from over-body downforce to the more efficient underbody is reflected in the contrast in shape between the monocoques of the 1990 Ferrari 641 and last year’s SF70H model. Sidepod inlets tended to be narrow and tall to minimise the section change around the cockpit and radiators. Now the radiator inlets are tiny, reflecting the improvement in cooling efficiencies of radiators, the lower heat rejection of the engines and how the airflow is now accelerated much harder towards the inlets. What can also be seen is how the current carbon fibre tubs incorporate the bodywork rather than having separate panels over the top of the tub as in the 1990 car.
Source : https://www.formula1.com/en/latest/technical/2018/6/tech-tuesday--france-flashback--how-f1-looked-in-1990.html