A [A] radiator positioned so that it is parallel to the ground would certainly decrease the drag of a kart, but it is not used in this position not so much for a regulatory issue, but because it would not be efficient at all in terms of heat exchange, thus requiring a duct to convey fresh air (in this regard, read “Technical Focus | New-Line Racing VMa-K: revolution in the world of radiators”, editor’s note). It is also true that [B] a radiator placed in a perfectly perpendicular position with respect to the ground would give an increase in the frontal surface and therefore in the cx, compared to the classic [C] “lying back” position. A radiator, however, is not a closed surface, but is made of channels and corrugated (the fins that allow heat exchange). And the corrugation, if the radiator is perpendicular to the ground, in turn becomes parallel to the ground, and therefore results in a lower pressure, because the air finds less of an obstacle in crossing the radiant mass than when a radiator is “lying back ” and the corrugated part “is a bit like a wall ”. Placed in this way, however, precisely because the air passes through it too easily.