Tuesday 18th February 2014

BMW 4 Series Convertible: Review

Wind in the hair motoring for four in BMW's 4 Series drop-top

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For those familiar with the 4 Series Convertible's predecessor, the E93 3 Series Convertible, the important figure to note is the 40 per cent increase in torsional rigidity of the new model over the old. Weight has also been reduced by up to 20kg model-for-model, despite the new iteration being a little bigger in all dimensions. Compared to the last of the 3 Series Convertibles this new model also has a longer wheelbase, a wider track front and rear and shorter overhangs, too.

4 Series Convertible: what goes up...

That should all be very promising because the outgoing model was, for a four-seat convertible at least, a pretty good steer. The evidence points to this new model being even better, then.

BMW lists dynamics as one of its three priorities for the 4 Series Convertible, along with efficiency and functionality. To that end this model has bespoke suspension tuning and a lower centre of gravity compared to the current 3 Series saloon, along with the signature 50:50 weight distribution.

Wobble board
There are a couple of points that will check our early enthusiasm, though. 40 per cent increase in rigidity or not it remains true that slicing a third out of a contained structure will diminish its integrity, and past experience of our own 435i coupe long termer has proven that even the fixed-head version falls some way short of being an electrifying drive.

...can also come down (but not over 18km/h)

The folding metal roof has been improved to better keep wind noise and the elements at bay, and it can be retracted in 20 seconds at up to 18km/h. That looks reasonable on paper, but in practice it feels little quicker than a brisk walk. Best make sure you do have 20 seconds to hand before dropping the roof at the lights.

The 4 Series Convertible will be available with three engines at launch; a four-cylinder diesel, a four-cylinder petrol and a six-cylinder petrol, all turbocharged. It's the range-topping 435i that we drive here, complete with eight-speed automatic gearbox.

What stands out first is the quality of the cabin, shortly followed by the drivetrain, which is perfectly suited to a car of this nature. The gearbox shifts quickly and cleanly while the engine pulls effortlessly from all points in the rev range. There's just enough six-pot snarl under hard acceleration, too, without it being unrefined or intrusive.

Roof down you'll be able to show off the best bit

Silky
With the roof in place there's no real evidence that it folds away, so well contained is wind noise. What's less impressive, though, is the ride quality, which on anything other than the very smoothest surfaces is never better than fidgety. The steering, meanwhile, is accurate enough, but never communicates anything of value back to the driver.

As long as the road surface allows, the Sport mode is best selected when the driver does want to start hustling. This adds weight to the steering, which does little to improve it, and firms the suspension up a touch. As the road begins to twist and turn and the driver commits harder to corners, there is a slight but definite sense that some rigidity has been lost compared to the coupe. There isn't any scuttle shake and nor is there any unwelcome vibration in the steering column, but it's clear that the suspension tuning has been compromised and there is, as a result, a degree of imprecision at turn-in and a lack of agility in rapid direction changes. A notch or two back from maximum attack, though, the 4 Series Convertible does carry plenty of speed along a challenging road with enough composure to encourage the driver to continue at such a pace.

Does the job but you can fill in the blanks...

For the role this car is intended to fulfill, it's only the slightly firm ride on the kind of surface that makes up most of our road network that deserves any criticism. That aside, and particularly with this drivetrain, the 4 Series Convertible is a highly accomplished four-seat drop-top.

 

 

 

 

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BMW 435i Convertible
Engine: 2,979cc 6-cyl, turbocharged
Transmission: 8-speed automatic, rear-wheel drive
Power (hp): 306hp@5800rpm
Torque (lb ft): 295lb ft@1,200-5,000rpm
0-62mph: 5.5sec
Top speed: 155mph (limited)
Weight: 1,825kg
MPG: 37.7mpg (claimed)
CO2: 176g/km
Price: £44,970

 

 

 

[RoverP6B]

I'd rather have an E92 330i, thanks. An overweight folding-hardtop convertible strikes me as being a car more for posing in than a serious driver's car.

[RoverP6B]

AudiWurst said:

Presume you're aware the E9x was a folding hardtop as well??

The E92 was a fixed-head coupe. The E93 was the wobbly poser's blancmange.

[RoverP6B]

I would prefer the E46 in some ways, yes, but that's now a 20-year-old design so it's not fair to compare. I've been a passenger in an E93 M3 with the top down and it felt distinctly wobbly. The E90 series has only just gone out of production and there are still new examples around to be had. I'm sorry, but nothing will EVER tempt me to buy something turbocharged or with questionable torsional rigidity. I enjoy a rigid bodyshell and natural aspiration (with the sharp throttle response that brings) too much.

[RoverP6B]

I'm with the Cadillac engineers in saying that the E46 was the best-driving 3-series of all - and to my eyes it's the prettiest. However, this is about what you can get new and there are still some new E92s on dealer forecourts.

[RoverP6B]

kambites said:

Now that is lovely.

Betty Haig had (and raced) one!

[RoverP6B]

redroadster said:

Yes they will sell loads, german cars are what most people aspire to hence why germanys economy is so strong look at france with citroen ,renault,peugeot.........

That's an extremely simplistic and inaccurate view of why Germany's economy is healthier than France's.

[RoverP6B]

May be so when you have the roof up. Roof down, no way - and shifting all that weight backwards will change how the front end behaves for the worse. I'm not saying the E46 is perfect, it isn't and I hated mine (318i Touring, slowest most gutless useless heap I've owned since I inherited my mother's Volvo 340!). I just do not like the whole idea of a folding hardtop convertible.

[RoverP6B]

kambites said:

Why would opening the roof change the front-end for the worse? One thing I'm not a far of with most BMWs is the weight distribution - 50% over the nose is too much for my preference. Opening the roof moves the CoG backwards and downwards, both of which are good in my book. Of course it will also raise the polar moment of inertia a bit, which isn't so good.

You put the weight of the roof further back, you're moving away from the 50:50 weight distribution - and, while you can set a car up for its weight distribution, short of active suspension, you can't tune it for two significantly different weight distributions. Oh, and BMW have less weight over the nose than most of their rivals (especially Audi!).

[RoverP6B]

jdw1234 said:

Would you really notice on a sunny Sunday afternoon, roof down on your way for a pub lunch though

On the roads round here, I'd certainly notice the loss of rigidity. Even my 5-series Touring can be felt to flex a little on arguably the worst (well, most challenging) B-roads in the country. I would also definitely notice the front end going light.

[RoverP6B]

kambites said:

Of course, but for me perfect weight distribution for a RWD car is about 40:60 F:R so it will bring it closer to that. As for how the suspension is setup, who knows whether it's designed primarily for roof up or roof down - I suspect it's a compromise of the two. I very much doubt I'm a good enough driver to tell the difference made by moving 50 odd kg backwards and downwards a couple of feet in a 1.8 tonne car anyway.

Lets be honest, the 4-series is hardly going to be the sharpest of driving tools any form, let alone the cabriolet.

Edited by kambites on Tuesday 18th February 16:53

How is an unbalanced weight distribution better than a balanced one? Next thing you'll be telling us Porsche have been wasting their time pushing the 911 flat six ever further forward and putting more weight in the front... a 4-series coupe could actually be quite a nice thing to drive, but Christ, a 1.8 ton folding hardtop convertible thingy... no way!

[RoverP6B]

kambites said:

Turn that on its head. Why is it "perfect" to have half the weight over each set of wheels. The two axles aren't performing the same roles.

Light nose, heavy arse: overlight steering, pendulum effect, lift-off oversteer.

Heavy nose, light arse: heavy steering, understeer, poor traction if it's RWD, possibly also lift-off oversteer.

[RoverP6B]

kambites said:

You didn't answer the question. Obviously there needs to be a balance but why is that balance 50:50?

In (non road-car based) racing cars in series where the weight distribution is unlimited but the cars can only be 2WD, what weight distribution do people go for? You can bet it's not 50:50.

Anything other than 50:50 is by definition unbalanced. What works on a racetrack is not the same as what works on the road. Race cars can be stiff enough to tune out some of the effects of unbalanced weight distribution, weight transfer and so on - not so with road cars.

[RoverP6B]

HumbleJim said:

Grandfondo said:

What happens if you put suit cases and passengers in the back of your precious 50/50 car?

I think it's okay if you fold the back seats down.

Are two passengers and a bit of luggage really likely to weigh as much as that bloody great folding hardtop and its mechanisms?

[RoverP6B]

g35x said:

The sharp throttle response that only a e39 520 can provide

To be honest I don't think BMW will be losing sleep over you putting yourself out of the buyer pool, in fact I don't think any manufacturer cares for that matter given your purchasing history.

For the record I have a E93 M3 ... sure I would have preferred the E92 but as with most things in life buying a car is ultimately a compromise (performance, utility, cost). The roof down allows you to experience the glorious engine note of the V8 and enjoy the car more in day to day driving conditions

You'd be surprised about that 520. It's slow to 30 but it really does pull strongly - no lag, precious little inertia, it really likes to rev (and in fact it feels like it's still got plenty more to give when the limiter kicks in - I'm going to see about what would be required to lift the rev limit without nuking the engine). I've stuck with it for the simple reason that I LIKE IT. I've tried the newer BMWs and I just can't get on with them. Right now, there's nothing new that I want. I know I'm far from alone in feeling this way. My choice is as valid as yours and vice versa.

[RoverP6B]

Ozzie Osmond said:

I'd be looking at the soft-top 1 series (2 series) or maybe a used 6 series if you want a bigger car.

Tried them both in the dealership - I simply couldn't fit in them. With the seat sitting as low as it went (in both), my eyes were level with the top rail of the windscreen.

[RoverP6B]

g35x said:

Appreciate the response, but it seems to me you look at every modern vehicle and pick fault to justify your own decision to stay with your E39, which i agree is a classic in terms of BMW. Just looking through your posting history you've basically dished out the same view over and over again like a broken record (e.g. no turbos, no trick suspension, no dual-clutch, no piped in engine noise).

You slate the diesel F10 520d as having a narrow power band, and the E93 M3 Convertible for being like a 'blancmange'. What you aren't saying it that the E9x M3 range has a glorious engine that you can wind up to over 8,000 rpm, and that the structural rigidity of the F10 is far superior to the E39. Both are objectively far superior to your car in almost all performance measures. The E93 M3 clearly isn't the last word in dynamics, but it can still show the E92 335i a clear pair of heels on tight tracks and that alone is impressive.

It's great to have an opinion but everyone knows your stance on modern cars and equipment loud and clear ... message received.

No trick suspension? Where have I said that? I have immense admiration for the likes of Citroen and McLaren on that front. The E9x M3 engine is quite nice, but it sounds rather bland to my ears - the S50/S52/S54 straight six sounds so much more musical to me. The E39 I bang on about because the major parts of it really are very good. That's not to say I can't find fault with it - I could reel off a litany of niggly little issues that conspire to reduce the enjoyment of owning the bloody thing. However, the way it handles, responds and even just settles down on the motorway with the engine barely audible (despite the addictive induction snarl as I floor it in second up slip-roads)... BMW just got it so damn right there. I'd have bought a 530i if I'd known how long the 520i would take to get to 30mph, though - a classic case of mixing eBay and beer! Regarding the E93's torsional rigidity, having ridden in one with the top down, it just felt soft and wobbly - more a quick boulevard cruiser than a genuine sports car. I was also, to be honest, surprised how heavy it is. I know that someone here ("Cerb4.5lee", if I recall correctly) has observed that 295 lb/ft isn't that much for such a heavy car - enough for it to be quick, but it won't trouble the Ferraris of its time in the way an E36 or E46 M3 will. That BMW's arguably most famous and prestigious sports car ended up weighing the wrong side of 1700kg... they need to stop making models bigger each new generation. Of course the bloody customer clinics will say they want a bigger 1/3/5 series - but the marketing men should reply with 'Yes, we make one of those. It's called the 3/5/7-series'.

F10 - it didn't HAVE a power band. It had a power wallop-over-the-head-with-a-sledgehammer. Also, despite it being a foot longer and a fair bit wider than my E39, I couldn't fit my bike in it, not anyhow. It goes into the E39 with no problems whatsoever. The F10's boot is actually a lot narrower than the E39's. God knows what all that dead space is for. I think the next purchase I make will be a Mercedes E-class estate...

[RoverP6B]

Grandfondo said:

I would be very surprised indeed if it had more go than an asthmatic budgie!

It goes like an asthmatic budgie to 30mph, certainly!

However, once you've overcome the basic inertia of lugging around 1680kg, it's surprising how strongly it pulls. As I said, the engine feels like the rev limiter cuts in too early, and I'm going to see about raising it. Even at triple-figure speeds, if you then floor the accelerator, there's no waiting and wondering where all the power has gone - it just goes. I haven't had it all the way to the book figure top speed of 139mph, but I have no doubt it can achieve that. Realistically, that's enough to land one in prison if caught on public roads, it's as much as you can achieve in most road cars on most racetracks, it's as much as you're going to get even on most autobahns. I'd like more torque and/or more engine RPM, certainly, but I honestly don't need more power. It used to be that over 100bhp/ton (this is 102) was quite enough for a car to be considered quick. My wife's old Peugeot 205 was only 84bhp/ton and that was quite fast enough to scare one's self slightly, driving the wheels off it through the Pyrenees, on a Stelvio-like mountain pass. That was a joyous experience, and anyone who thinks a 2-ton barge with an autobox and 500+ bhp is motoring nirvana should go and get a basic 1.4 litre Pug 205 and thrash the wotsits off it for a while. I guarantee that the M5/whatever will feel utterly dead after that, even though the Pug wouldn't see which way it went in a straight line. Actually, that is my one major criticism of the E39 - it's so bloody heavy (albeit 300kg lighter model-for-model than the F10/11). Use of aluminium or reinforced plastic panels for the door skins, front wings, tailgate and suchlike would have shaved a lot of weight off it and made it more rewarding to drive. However, it's easier to forgive a family estate its roughly 1.7 ton mass than a sports coupe like an M3!

[RoverP6B]

Grandfondo said:

"pulls strongly"

It would struggle to pull a sailor of your sister!

A - you'd be surprised. The balance and low inertia of the N/A straight six means it goes far better than 170hp suggests. 100bhp/ton is enough for a quick car in most people's books, I'd just like more torque.

B - I'm an only child.

[RoverP6B]

PHC said:

Ultimately in every day driving for an owner who's not going to go to a circuit why not have a convertible, and if you are going to get a convertible nothing better than a folding tin top BM.

I'm looking forward to driving this new one.

Because a convertible flexes like hell even at fairly low speed on the average British B-road - and the E93 is no exception, unless you keep the top up (in which case, why wouldn't you have the stiffer and more handsome E92?).

[RoverP6B]

Bungleaio said:

You don't half talk a load of bks.

The usual ad hominem attacks, I see. E93s flex, fact. Even my E39 Touring can be felt to flex at times over some of the worst rutted off-camber roads round here.