Comparison: BMW 420d Gran Coupe versus 330d saloon

Read the full BMW 3-series review

This new 4-series is a handsome thing. It makes the 3-series look unexpectedly dumpy and awkward – all straight-sided from the rear end and ill-proportioned in profile.

The frameless doors, elegant roofline and eye-catching details of the 4-series all contribute to a much more appealing overall impression than the 3-series gives. Which is saying something considering that, to these eyes, a 3-series is still about the best-looking ‘normal’ compact exec you can buy.

On the inside, the cars are much less easily separated. To be frank, the 4-series’ cabin designers ought to have done more. The architecture, material richness and finish of both fascias are identical. You sit slightly lower in the 4-series and feel a touch more intimately cocooned by the nearer driver’s window and roofline, so the 4-series feels a bit more special, but not much.

In the back, the relative shortage of passenger space in the 420d is big enough to notice. And although the 4-series’ boot is easier to access, it’s slightly narrower and shorter than that of the 3-series.

It’s not often that a road tester gets handed two cars as precisely matched as these to compare. Then again, all-BMW twin tests aren’t normally as interesting as those involving other brands as well. This one’s certainly not short of intrigue or subtlety, though.

BMW supplied our pair with matching xDrive four-wheel-drive sport automatic transmissions and similar adaptively damped M Sport suspension set-ups, in similar M Sport trims – even with identical alloy wheel sizes and tyres. And yet they are more different to drive than the gap between their respective engines and performance levels would suggest. And that, in itself, is a pretty big gap.

There are, of course, fundamental differences between a 3-series and a 4-series that account for some of the disparity between their driving experiences. Lower and wider of both body and axle tracks, the 4-series has its own chassis tuning, intended to convince you that it’s more spry and precise than its cheaper sibling. It works.

The Gran Coupé feels a shade more taut in its body control and crisp in its directional responses than the saloon. Although outright grip levels are as evenly matched as you’d expect and both cars have excellent cornering balance, the 4-series is just a little bit more eager and direct as you turn the steering wheel.

Read the full BMW 4-series Gran Coupé review

The 330d hits back because its surfeit of power and torque makes it more engaging once you’re settled in a corner, driving out. Simply put, a 420d doesn’t have the urge to feel characteristically rear driven when you want to have a bit of fun. A 330d does. Even in xDrive form, it’ll wiggle its rear end and take a poised, neutral attitude out of a bend under power. 

In that microcosm, you could say that the 330d handles like a fully fledged BMW and the 420d doesn’t – although it’d be harsh on the 4-series to apply that generalisation more widely.

On steering feel, for example, the 4-series’ helm feels a tiny bit more fluent and connected at bumbling speeds, but both systems come alive as you load them with cornering forces, and both telegraph ebbing grip well enough.

Working against the 4-series is an occasionally nagging ride. On smooth A-roads and motorways, the 420d’s chassis flows between gentler dips and bumps well, but on B-roads it’s too firm. Even in Comfort mode on the adaptive suspension, it feels short on wheel travel and slightly aggressively damped.

The coarseness of the 420d’s engine, its relative lack of potency and that patchy ride contrast starkly with the 330d in all departments. It may not be that the 3-series’ 3.0-litre straight six is markedly quieter than the 420d’s four-pot, but it seems that way because it’s so much more smooth and suave.

On power delivery, the 330d is so much more flexible, as well as stronger absolutely everywhere, than the 420d. The 330d is every inch a distinguished premium product. And it’s a much more rounded, luxurious machine than the 4-series as well, thanks to a chassis that can be supple and forgiving at one moment and still stout and engaging the next.