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.

August 23, 2013
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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.

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.

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.

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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