What is it?
The entry-spec model we're testing here is likely to be the biggest seller in the BMW 4-series range. There are three very good reasons for this: it emits 124g/km of CO2, it can cover a claimed 60mpg on the combined cycle and it's the second cheapest model in the range.
Like all 4-series models, the 420d shares its same basic architecture with the F30-generation 3-series. It is slightly longer and wider than the Three, but substantially lower, which means it has the lowest centre of gravity in BMW’s model range.
The 420d is powered by the same 181bhp, 2.0-litre turbodiesel as the 320d. It makes peak power at 4000rpm and hits 280lb ft between 1750-2750rpm. BMW claims a 7.5sec 0-62mph time and a top speed of 149mph.
An eight-speed automatic gearbox and BMW’s xDrive four-wheel-drive system are available as options, but the model we're testing has the standard-fit six-speed manual gearbox powering the rear wheels.
Our test car is also in SE specification, the first of five trims. It includes leather upholstery, 17in alloy wheels, two-zone air-conditioning and USB connectivity as standard.
What's it like?
The BMW 420d is particularly sweet. Its 2.0-litre 4-cylinder turbodiesel offers huge flexibility, and is far more potent than its 7.5sec 0-62mph time suggests. It is strong in the mid-range, but lacks the last few degrees of sparkle and responsiveness afforded by the larger six-pot diesels.
Refinement on the move is very good, but at tickover – particularly at start-up – there’s some typical four-cylinder clatter.
The six-speed manual gearbox is far from the slickest we've encountered. Initial springy resistance to the lever being slotted through the gate, coupled with quite long clutch pedal travel, means the 420d has a shift that rewards preciseness and patience, but feels less at home when you're trying to push hard up the gears.
Elsewhere the 420d is much the same as the rest of the 4-series range. It's a neatly balanced chassis that offers a grown-up brand of sportiness, wrapped up in a handsome and hugely desirable body.
The entry-level SE model tested here features a decent level of kit, which helps to justify its £3000-plus premium. With smaller wheels and a more pliant suspension configuration, ride comfort and refinement is really rather good. It’s just a shame that there’s rather too much lateral movement when cornering hard. The £750 adaptive M Sport suspension would seem like a worthwhile option.
Should I buy one?
It's maybe unsurprising that the 4-series' maturity suits the 420d’s relaxed sensibilities, but it would perhaps be better suited to an automatic transmission. However, given that it's so closely related to one of our favourite new cars, the 3-series, it's still an outstanding model.
Little of that will matter too much to 420d buyers, though – the promise of an easy 50mpg, coupled with appealingly low benefit in kind bills for such a desirable model, will be the main draws.