The BMW Z4 (E85) 2.5si Steptronic, produced from 2006 to 2008, represents a significant iteration of BMW’s popular roadster. This variant, part of the E85 LCI (Life Cycle Impulse) facelift, aimed to blend performance with convenience, offering a more accessible entry point into the Z4 range while still delivering a distinctly BMW driving experience. Positioned as a mid-range offering, it sat above the 2.0i models and below the high-performance 3.0si, appealing to drivers seeking a balance of power and ease of use. The E85 generation Z4, as a whole, was BMW’s replacement for the Z3, moving towards a more sophisticated and modern roadster design.
Technical Specifications
| Brand | BMW |
| Model | Z4 |
| Generation | Z4 (E85 LCI, facelift 2006) |
| Type (Engine) | 2.5si (218 Hp) Steptronic |
| Start of production | 2006 |
| End of production | 2008 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Roadster |
| Seats | 2 |
| Doors | 2 |
| Fuel consumption (urban) | 12.8 l/100 km (18.4 US mpg) |
| Fuel consumption (extra urban) | 6.8 l/100 km (34.6 US mpg) |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 6.9 sec |
| Acceleration 0 – 62 mph | 6.9 sec |
| Acceleration 0 – 60 mph | 6.6 sec |
| Maximum speed | 238 km/h (147.89 mph) |
| Weight-to-power ratio | 5.9 kg/Hp |
| Weight-to-torque ratio | 5.2 kg/Nm |
| Power | 218 Hp @ 6500 rpm |
| Torque | 250 Nm @ 2750 rpm (184.39 lb.-ft. @ 2750 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | N52B25A |
| Engine displacement | 2497 cm3 (152.38 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 82 mm (3.23 in.) |
| Piston Stroke | 78.8 mm (3.1 in.) |
| Compression ratio | 11:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | DOHC |
| Engine oil capacity | 6.5 l (6.87 US qt | 5.72 UK qt) |
| Kerb Weight | 1290 kg (2843.96 lbs.) |
| Max. weight | 1585 kg (3494.33 lbs.) |
| Max load | 295 kg (650.36 lbs.) |
| Trunk (boot) space – maximum | 260 l (9.18 cu. ft.) |
| Fuel tank capacity | 55 l (14.53 US gal | 12.1 UK gal) |
| Length | 4091 mm (161.06 in.) |
| Width | 1781 mm (70.12 in.) |
| Height | 1299 mm (51.14 in.) |
| Wheelbase | 2495 mm (98.23 in.) |
| Front track | 1473 mm (57.99 in.) |
| Rear (Back) track | 1523 mm (59.96 in.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, automatic transmission |
| Front suspension | Independent, type McPherson with coil spring and anti-roll bar |
| Rear suspension | Coil spring |
| Front brakes | Disc |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Tires size | 225/50 R16 |
| Wheel rims size | 16 |
Powertrain & Engine Architecture
At the heart of the 2.5si Steptronic lies the N52B25A, a 2.5-liter inline-six engine. This engine is a naturally aspirated powerplant known for its smooth operation and responsive power delivery. The N52 featured double VANOS (variable valve timing) on both the intake and exhaust camshafts, optimizing performance and efficiency across the rev range. Fuel delivery was handled by a multi-port fuel injection system, providing precise fuel metering. The engine produced 218 horsepower at 6500 rpm and 250 Nm (184 lb-ft) of torque at 2750 rpm. The “Steptronic” transmission refers to BMW’s 6-speed automatic gearbox. This transmission offered both fully automatic operation and a manual shift mode, allowing drivers to have more control over gear selection. The transmission was tuned to provide smooth shifts and complement the engine’s characteristics.
Driving Characteristics
The 2.5si Steptronic offered a comfortable and engaging driving experience. While not as overtly sporty as the 3.0si, it provided ample power for both everyday driving and spirited excursions. The automatic transmission, while convenient, did slightly diminish the raw acceleration compared to the 6-speed manual version. The 0-60 mph time of around 6.6 seconds was respectable for its time. The engine’s torque curve provided good mid-range punch, making it easy to overtake and merge onto highways. The rear-wheel-drive configuration contributed to balanced handling, and the suspension provided a comfortable ride without sacrificing too much cornering ability. The automatic transmission’s gear ratios were optimized for a balance of fuel efficiency and performance.
Equipment & Trim Levels
The 2.5si Steptronic came reasonably well-equipped as standard. Typical features included leather upholstery, automatic climate control, power windows and locks, and a premium sound system. Optional extras were plentiful, including sport seats, a navigation system, a Harman Kardon audio upgrade, and various cosmetic enhancements. The interior design was driver-focused, with a clear and intuitive layout. The dashboard featured metallic trim accents, and the seats provided good support. The Z4’s retractable hardtop, a key feature of the E85 generation, provided excellent security and weather protection when raised, and a more open-air experience when lowered.
Chassis & Braking
The Z4 E85 utilized a McPherson strut front suspension and a multi-link rear suspension, providing a good balance of ride comfort and handling precision. The 2.5si typically featured disc brakes on all four wheels, providing ample stopping power. ABS (Anti-lock Braking System) was standard. The chassis was designed to be relatively lightweight, contributing to the car’s agility. The standard tire size was 225/50 R16, providing good grip in most conditions. The suspension tuning was slightly softer than the 3.0si, prioritizing comfort over outright track performance.
Market Reception & Comparison
The Z4 2.5si Steptronic was generally well-received by automotive critics. It was praised for its smooth engine, comfortable ride, and well-appointed interior. Some reviewers noted that the automatic transmission dulled the driving experience slightly compared to the manual version. Compared to the 2.0i, the 2.5si offered a significant performance upgrade. Compared to the 3.0si, it was more affordable and offered slightly better fuel economy. Fuel economy figures were around 18.4 mpg in the city and 34.6 mpg on the highway. Reliability was generally good, although like all BMWs of this era, preventative maintenance was crucial.
Legacy
The BMW Z4 E85 2.5si Steptronic remains a popular choice among used car buyers seeking a stylish and engaging roadster. The N52 engine is known for its durability, although regular oil changes and valve adjustments are essential. The automatic transmission is generally reliable, but it’s important to check for smooth shifting and proper operation. Today, these Z4s represent a good value proposition, offering a premium driving experience at a relatively affordable price point. The E85 generation Z4, and particularly the 2.5si variant, has cemented its place as a modern classic, appreciated for its blend of performance, style, and driving enjoyment.
