RS4 replacement is a 2.4-tonne plug-in hybrid, yet the engineers promise it’s much more fun to drive I don’t think it’s coincidental that Audi decided to let us drive the new RS5 Avant soon after revealing its technical details.If you’ve seen any online reaction to its unveiling, you may have noted some dismay that the kerb weight is 2355kg (hatch) or 2370kg (estate). The latest BMW M5 elicited a similar response; both are high-performance plug-in hybrids. Those are big numbers, so there are preconceptions to dispel, but Audi thinks that actually driving the RS5 will do the trick.The car is a direct replacement for the RS4 but with a different name, because Audi briefly revised its naming strategy and this is a hangover from that. Maybe they had already made the badges.And it’s as heavy as it is because making a PHEV is one of the few options left open to a company that wants to make super-saloons. A fully electric sports saloon could be perceived as insufficiently exciting, as modest RS E-tron GT sales suggest. And the days of simply fitting a whopping engine to an executive estate are largely behind us: German tax rates are much kinder to cars with a 50-mile electric range and there are many other places where a reduced headline CO2 emissions figure is advantageous. In the US they mind big engines less – at the moment, anyway – but Audi couldn’t have known that when it started this car's development.And so here we are with Audi’s first RS PHEV.