Agility Champion

More than just a two-door 3 Series, the new 4 Series Coupe offers improved driving dynamics to go with its upscale accoutrements.

Photo: Agility Champion 1
August 23, 2013

Klaus Fröhlich wants you to be happy. He wants you to be fast, too—easily, effortlessly so, which is why BMW’s VP in charge of small and medium cars developed the new 4 Series with a ton of mechanical grip, excellent aerodynamics and near-perfect weight balance between the two axles. There’s more to it than that, of course, but Fröhlich is keen to emphasize the 4 Series’ driving dynamics, particularly as they distinguish BMW’s new two-door coupe from its 3 Series sedan sibling.

“When I came to the project, it felt just like a 3 Series,” Fröhlich says.

That wouldn’t do. This was a 4 Series, after all, not a two-door 3 Series, and the new nomenclature had to reflect a different character as well as configuration. The 4 Series had to be sleeker and more upscale, and it also had to be sportier, appealing to enthusiasts who prized driving engagement over practicality.

Photo: Agility Champion 2

With that in mind, revising the electric power steering assist was first on Fröhlich’s agenda —he’d read the criticism of the 3 Series’ numb steering and wanted no such complaints about the new coupe. Even more than horsepower figures or zero-to-60 times, steering feel would define the 4 Series to its driver, and it would be the most tangible result of the development team’s efforts.

Good bones

To get the steering right, they’d have to maximize the 4 Series’ dynamic performance overall, stiffening the chassis and enhancing the connection between the vehicle and the road. Good steering feel, Fröhlich says, starts not at the rack-and-pinion but at the rear axle, so the development team spent considerable attention making the five-link rear axle (in lightweight steel) as rigid as possible. It doesn’t bolt directly to the body like the rear axle on the M5 and M6, but it does use bushings that are as stiff as they can be without sacrificing the ride quality demanded by customers of BMW’s regular production cars.

Photo: Agility Champion 3

The front axle, too, was made stiffer than that of a 3 Series with a pair of extra torsion bars that run backward toward the firewall. These torsion bars function like an X-brace, the part originally developed by BMW Motorsport to connect the front subframe to the body of the E36 M3 Convertible as well as the E36 M3 coupe in various special edition and racing homologation models, and which has since become a staple of M-car chassis tuning. Stiffer bushings were added at the front just as at the rear, and the whole car was made to ride as low as possible—its 500mm-high (19.7-inch) center of gravity is the lowest among all series production BMWs. Further improving mechanical grip and stability, the 4 Series rides on wider tracks than its sedan counterpart: 60.8 inches at the front vs. 60.3, and 62.8 inches at the rear vs. 61.9.

None of that would be communicated effectively if the steering mechanism itself weren’t just right, and Fröhlich was especially keen to avoid duplicating the 3 Series’ relatively mute on-center feel. The overall ratio is fairly similar—15:1 in the 4 Series, 15.1:1 in the 3—but the ratio increases more rapidly as the 4 Series’ wheel moves away from center, becoming a stout 10:1 at maximum lock. That may sound fairly high, but it’s right in line with the ratios used during the E36 era, and on the late-production E46 M3 with Competition Package.

As far as the type of information that the wheel delivers, it’s far better than that of the 3 Series, yet it’s somewhat muted compared to what comes through the chassis itself. Drive over a series of lane-departure ridges, for instance, and you’ll feel them more sharply through the floor than you will through the steering wheel. That’s because the electric power steering system can be tuned to filter not just the volume of information but the quality. It does so by damping certain frequencies, in particular those at the higher end of the spectrum that fail to add much information about available traction and merely increase driver discomfort over rough surfaces like roads that are being repaved.

Photo: Agility Champion 4

On the street, the 4 Series’ steering felt just about right. It wasn’t as good as that of a new Porsche Boxster, the current feel leader with electric steering assist, but it did feel on par with that of a Porsche 911, which in an unusual twist is actually inferior to the Boxster in its current generation. Compared to the 3 Series, the 4 felt like heaven.

Neutral state

Even more impressive, however, was its nimble handling. On the twisty back roads of our test route, the car felt lighter and more agile than its 3,610-lb. curb weight would suggest…although we’ll admit that our sense of vehicle weight is somewhat skewed by having driven so many that top 4,000 lbs. lately.

Photo: Agility Champion 5

In the case of vehicle mass, however, where matters more than how much. In the fore and aft direction, the 435i places 52.1% of its weight over the front axle and 47.9% over the rear, which isn’t quite the perfect 50/50 that BMW shoots for but is certainly close enough. Even more important, we can sense that most of that mass is concentrated well toward the center of the vehicle, where its effect on handling is minimized; for turning agility, nothing beats a low-slung mid-engine car, and the closer you can get to that ideal the better. We’ve already determined that the 4 Series trumps all other BMWs where center of gravity is concerned, and we suspect that it also sets the standard for center of mass. We can’t quantify that impression, but we can feel it.

Weight at a vehicle’s perimeter acts like a pendulum when the vehicle changes direction, and changing direction more than once in quick succession forces a delay until that weight stops moving and the car takes a set. There’s very little waiting in the 435i, something that becomes even more noticeable when we leave the public roads around Lisbon for a few laps of the small but superbly fun Estoril circuit.

Upscale comforts

Photo: Agility Champion 6

This tight little track was used for Formula One before the cars outgrew it, and it’s still used for MotoGP races. It’s a neat circuit that’s easy to learn while still including a few long straights and a good variety of corners—from long and fast to ultra-tight—that each makes its own demands on a car’s performance.

The 4 Series acquits itself well in all of them. As Fröhlich promised, the car is exceptionally well balanced, its attitude easy to adjust with the throttle. Handling is fairly neutral, with a slight bias toward understeer that only makes itself felt if a corner is entered too fast; similarly, oversteer is encountered only when getting on the gas too soon coming out of a turn. In other words, you’ve got to do something wrong to get anything other than easy, neutral handling, but even then the 4 Series’ attitude responds perfectly to a steering correction or throttle adjustment.

Steering response and driving dynamics play a big role in all of that, but so do creature comforts and ergonomics. The 4 Series isn’t drastically different to the 3 Series in either regard, but its cockpit is an even more splendid place to work when you want to cut a fast lap. We drove a Sport Line 435i whose seats offered perfect support and plenty of bolstering without intruding on elbow movement, and whose steering wheel felt utterly perfect in our hands. Small in diameter and fairly fat, it might be BMW’s best-ever steering wheel, even without Alcantara. To top it all off, the interior is beautifully finished, with high-quality leather nicely stitched throughout. It’s not on the level of a 6 Series, of course, but it surpasses the standard 3 by a good margin.

Photo: Agility Champion 7

More importantly to enthusiasts, the new 4 handles better than the 3, as well. The familiar N55 six-cylinder’s 302 hp and 295 lb-ft allow both sedan and coupe to generate considerable speed, especially with the rapid-fire eight-speed automatic, but that greater velocity is easier to control in the more stiffly-sprung 4 than the softer 3. At Estoril, selecting Sport or Sport+ provided well-controlled damping for smooth weight transfer under braking and acceleration and very little body roll in corners—far less than a 3 Series in the same setting.

As the basis for the forthcoming M version, this is probably the best platform they’ve ever gotten at Garching—as good as the 435i Coupe is, we can’t help but imagine how much better it’s going to be as an M4.

For now, though, we’re perfectly content to enjoy it as a 435i. It’s quick, it handles, it’s comfortable, it’s sexy…it’s everything you could want from a BMW coupe. Most of all, it’s easy to go fast and have fun without feeling frantic in this new 435i, and that makes us happy.

Photo: Agility Champion 8

It makes Klaus Fröhlich happy, too.

“Mission accomplished!” he laughs.

Sidebar: The new 4: A shrunken 6

BMW has made much of the extra size of the new 4 Series over the 3 Series Coupe, particular the fact that its front and rear tracks are 45 and 81mm wider respectively than those of the outgoing E92 3 Series Coupe.
Not to diminish the importance of wider tracks, but the vital bit missing from these impressive statistics is that the 4 Series is based on the already larger F30 3 Series sedan. This means that the rear track of the new Coupe is just 22mm wider than its four-door sibling, the extra 11mm track width per side coming from bespoke wider hub carriers, with the center-point steering geometry and elastokinematics revised to suit.
In combination with an overall height down by 16mm and a body that sits 10mm closer to the ground, the changes add up to substantial dynamic benefits. On top of that, BMW has tuned the 4 Series suspension to match its more overtly sporting character. The result is a fine basic platform that will make the job of creating the forthcoming 440-hp M4 Coupe that much easier for M GmbH.
Moving off, the first thing you notice is how much more mature the car feels in the way it goes down the road. The real key to the improved ride is the new body shell that BMW says is 60% stiffer torsionally than that of the E92 3 Series Coupe. This is achieved through a combination of lightweight, high-strength steels, alloys and the flat section tubular braces that run from the front subframe to the bottom of the front bulkhead/sill areas. These braces alone stiffen the shell by between five and ten percent.
With the extra stability and poise from this setup coupled to the lower center of gravity, the engineers have been able to concentrate on making the car ride that much better, using progressive spring rates that start off softer than those of the E92 and end up stiffer towards the end of their travel.
In Comfort mode, the suspension is supple, even on the 19-inch wheels that equipped our 435i test cars. The extra millimeters in the wheelbase and track widths make a palpable difference here. In practical terms, the 19s perfectly suit a car of this physical size. The 20s will no doubt please some owners but are likely a bridge too far in terms of loss of ride comfort and the practical issue of potholes and other real-world road imperfections.
The M Sport suspension option takes the handling to the next level via uprated springs and anti-roll bars, with 19-inch wheels as part of the package. Basically, the hollow front anti-roll bar and thicker solid rear bar deliver ten and five percent increases in stiffness, respectively. Normally, a stiffer front end would encourage more understeer, but the ratings of the other suspension components have been recalibrated to rebalance this so that the net result is simply greater roll resistance and a slight reduction in understeer.
It’s a good match for the silky TwinPower Turbo N55 straight six. With 302 hp and 295 lb-ft, this engine has plenty of punch everywhere, and the ratios of the paddle-shift eight-speed automatic slur from one to the other with impressive speed and smoothness. It also blips the throttle precisely on downshifts, making you look like a hero to bystanders.
Before the year is out, BMW will offer an M Performance package that uses an ECU remap and freer-flowing exhaust to deliver 34 hp and 37 lb-ft more torque along with a limited slip differential. Even in standard form, the N55 is powerful enough to make the 435i a stupendous motorway muncher. Gliding along at an indicated 75 mph in top gear, it’s turning just 2,000 rpm. Yet when you need to go faster and push your right foot all the way to the carpet, the responsive software will instantly ask the gearbox to kick down one, two or even three ratios and wind the motor out to redline before upshifting to the next gear.
This contrast of character is one of the nice things about the 435i: It’s a long-distance cruiser one minute, a hard-charging GT the next. And even though it can blast to 62 mph in 5.1 seconds, it is also economical, sipping fuel at an average of 32.8 mpg in EU tests.
Up in the hills near Lisbon, the 435i’s eight close ratios once again came into play, punching the car out of tight hairpin bends with real verve just on torque. With the N55’s meaty torque curve always raring to go, it is very easy to exceed the mechanical grip of the rear tires, and you can feel the electronics working to keep everything in equilibrium as you rocket out of tight bends. Switch off the electronic nanny and power slides can last as long as you like.
I was happy, therefore, that BMW thoughtfully provided the Estoril circuit, where the 435i proved noticeably more focused than its predecessor. It turns in enthusiastically and is impressively stable through fast bends. The track session underlined my road impression that the 4 Series has BMW’s best electric power steering effort to date, with good weighting and a perfect turn-in rate in relation to the chassis. You don’t notice it, and that’s a good thing.
On the slower corners at Estoril, you need to get the entry speed right down to avoid having the stabilizing understeer transition into front-end push. However, there is more than enough grunt to alter the car’s attitude mid-bend, and this can be used to counter understeer by taking off some steering lock and bringing the tail ’round with power. The healthy torque curve means you can drive the whole track in third and fourth gears, and despite the high ambient temperatures on the day, the brakes worked tirelessly with good pedal feel.
The new BMW 4 Series Coupe is more than just a pretty face. It is a car with well-rounded abilities and a near-perfect marriage of style, performance and practicality. In many ways, it is a shrunken 6 Series Coupe, and that is certainly no bad thing.—Ian Kuah

Also from Issue 118

  • Ignatey Terzian’s 1974 2002 Turbo
  • 2013 F12 640i Convertible road test
  • Buyer’s Guide: The $9,000 3 Series
  • Interview: Product planner Paul Ferraiolo
  • F10 M5 Kelleners Sport KS5-S
  • 740-hp E36/8 Z3 M coupe
  • Len Heinz' pair of E30 M3s
  • Frank Stella's E9 CSL Art Car
  • How-To: E30 rear shock replacement
  • Team RLL's Racetech seats
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