BMW Alpina B4 VS Audi RS5

One of the key differences between the B4 and M4 is the ride. While the M4 can crash over bumps and generally be a little hard to live with, the crew in Buchloe have gone after a much more plush ride. And in that they have succeeded because the B4 S is a mighty fine cruiser. Bumps are dismissed with a haughty disdain, even Sport + silliness doesn't completely write-off ride quality.

Very impressive too, is the steering. While still not at Lotus Elise levels of feel (few cars are), the Alpina tweaks connect the your palms to the road with more clarity than what you'll find in the 440i or M4. Where the M4 particularly adds too much weight, the 440i is a bit more circumspect in that regard.

And then we come to the engine. The B58 six is a belter, better even than the N55 that preceded it. It's still a 3.0-litre straight six but is part of BMW's modular engine family that starts with a 1.5-litre triple in the Mini and 1 Series. The Alpina-spec turbos are noisier, the Akrapovic exhaust lighter and also noisier. It doesn't have the all-out crackle and pop of an Audi or Merc (perish the thought), but when you're on it, the B4 means business. The 660Nm of torque, available over a wide rev range, delivers a steel fist wrapped in a velvet glove and bubble wrap - the speed builds rapidly but smoothly. 

The approach to the chassis tune seems to be based on the driving talents of mere mortals on normal roads, which is kind of like the 440i. It's terrific fun to drive hard but it's very forgiving and patient. The great thing about it is that you wouldn't think twice about jumping in it for the long haul, so comfortable and quiet is the cabin. The M4 will leave it for dead on a winding road, but that's perfectly fine.

One irritant is the replacement of the admittedly cheap BMW gearshift paddles with weirdly non-tactile buttons. They're not particularly easy to use and, probably worse for a sporty car, unsatisfying. It's an odd detail with which to go off the reservation. Cheeringly, the eight-speed ZF is its usual perfect self, so you don't have to worry too much about manual mode or go old school and use the shifter.

With our time behind the wheel limited to the RS5 Coupe, we can only really report on how the two-door feels on the road, but given the prodigious power on offer, it's unlikely the addition of two doors is going to make the Sportback any slower. 

In short, the RS5 is thunderously fast, collecting speed with utter nonchalance thanks to this thick and endless-feeling supply of power unleashed whenever you plant your right foot.

It makes even the most ham-fisted attempts at cornering feel fast as lightning, with the power flow able to make up for every slow entry and exit by simply piling on pace between bends. 

But that's what you expect from an RS model, right? So perhaps more impressive is the RS5's ability to transform back into a relatively sedate urban cruiser when the red mist subsides. The suspension is firm, especially over rough road surfaces, and you do need to be a little careful with the accelerator to avoid that lurching feeling at every green light, but driven calmly, it doubles as a everyday car quite nicely.

Like in the RS4, we did find the gearbox felt a little quick to change at pace, shifting up or down at strange moments on the way into or out of corners, but you can reclaim control via the paddle shifters.