2007 BMW Z4 ROADSTERS AND COUPE: Contemporary Interpretations of the Classic Sports Car and Grand Touring Sports CarForty years ago American driving enthusiasts were in the midst of a great debate taking place in car magazines and at car club meetings. Precipitated by mass-production carmakers using the term 'sports car' to market what were essentially sedan-based products to the burgeoning youth market, the debate centered on defining the authentic sports car.
In the end most of the debaters agreed it was easier to determine what was not a sports car than to agree upon a hard-and-fast definition of what constituted a real sports car. But even at first glance, the most ardent automotive purist would declare that the 2007 BMW Z4 Roadsters and Coupe are authentic contemporary interpretations of the classic sports and Grand Touring car concepts.
The '07 Z4 lineup consists of three models: • 3.0i Roadster - powered by a 3.0 liter inline 6-cylinder engine producing 215 hp/185 lb-ft. torque
• 3.0si Roadster - powered by a 3.0 liter inline 6-cylinder engine producing 255hp/220 lb-ft. torque
• 3.0si Coupe - powered by a 3.0 liter inline 6-cylinder producing 225hp/220 lb-ft. torque
Each features firmly planted suspension, standard run-flat performance tires and state-of-the-art stability electronics anchored in remarkably rigid Coupe and Roadster body/chassis structures topped-off by a unique and captivating design. Inside, the driver can enjoy the Z4's innate sportiness while savoring extensive comfort and convenience features.
New features for 2007 include:
• Saddle Brown has been added to the Extended High Performance Leather offerings for the 3.0si Roadster and Coupe
• A Tire Pressure Monitor replaces the previous Flat Tire Monitor
• The Premium Package now includes a 4-year subscription to BMW Assist (previously 1 Year)
• Auxiliary audio input is now standard equipment
In 2006, BMW engineers and designers gave the Z4 its first major evolution. Heading an extensive list of updates and improvements were all-new, more powerful engines;
6-speed manual and automatic transmissions available on all models; more powerful brakes, standard 17-in. wheels and tires across the board, and a more advanced Dynamic Stability Control system.
And last year BMW introduced the Z4 Coupe 3.0si. As the Series' first closed-body model, the new Coupe encloses its two seats and a larger cargo area in a graceful fastback body that retains the Z4's unique aesthetic character while lòòking expressively new.
The Z4 Roadsters and Coupe share these features:
Performance & efficiency
• The N52 6-cylinder inline engine –
• Magnesium/aluminum composite construction
• Valvetronic variable intake-valve lift
• Electric water pump
• Volume-controlled oil pump
• Roadster 3.0i – 215 hp/185 lb-ft. torque
• Roadster and Coupe 3.0si – 255 hp/220 lb-ft. torque
• Optimized final drive ratios, numerically higher to further improve acceleration (Coupe ratios differ from those of Roadster 3.0si)
• 6-speed manual transmission standard on all models (former 2.5i model had a
• 6-speed automatic transmission optional on all models with:
• Shift paddles on §teering wheel
• Direct Selection of Manual shift mode via paddle downshift
• Sportier overall programming
Handling, ride & braking
• 17-in. wheels and tires standard on all models; 17-in. differentiated front/rear sizes as part of 3.0i Sport Package
| ||Vital Stats|
|Engine : 3.0 L., 6-cylinder|
Power: 255 hp
Torque: 220 ft-lbs
Engine : , 6-cylinder
Power: 330 hp
Torque: 262 ft-lbs
Engine : 3.0 L., 6-cylinder
Power: 215 hp
Torque: 185 ft-lbs
• Dynamic Stability Control system incorporates the following braking functions –
• Brake Fade Compensation
• Brake Standby
• Brake Drying
• Start-off Assistant
• Modulated ABS function, for smoother operationExterior design & function
• Front bumper assembly wîth large air intakes and rectangular foglights
• Stainless-steel exhaust tips (3.0si models only)
• Exciting metallic paint colors
Ergonomics, luxury & convenience
• Glove compartment: silicon damper for smoother opening/closing, and illuminated
• Rubber mats at bottom of door pockets
• Steering-wheel spokes trimmed in galvanic material in all versions
• Automatic climate control (optional 3.0i, standard 3.0si models) has galvanic trim for enhanced appearance, rubber surfaces for improved tactile feel
• Adjusting wheels for air vents also have rubber touch tactile surfacesThe Z4 Roadster body/chassis structure:
high rigidity enhances handling
'The correlation between chassis rigidity and athletic handling has long since ceased to be a mystery,' wrote Car and Driver in its April '02 issue, 'one is a prerequisite for the other.'
When BMW's structural engineers were developing the Z4, they created a body/chassis structure wîth exceptional stiffness for a roadster. The team achieved 21 Hertz – truly outstanding for a roadster, and close to the 25-26 Hz of today's BMW sedans. To attain this remarkable rigidity, the engineers incorporated a number of special structural features, including Y-form front structural members, ultra-strong side sills and underbody, 'thrust plates' that add rigidity to the front and rear suspension attachment points, and extensive use of high-strength steels. To save weight and help optimize front/rear weight distribution, the Z4 hood is of aluminum. Rollover protection is provided by an exceptionally strong windshield frame and two rollbars mounted behind the seats. Softtop: intelligent design, choice of manual or power
The Z4 Roadsters offer manual and power softtops, the latter available on both models as a stand-alone option or in the Premium Package.
Standard manual top. Intelligent design and engineering result in easy operation and excellent functionality:
• 1-hand release/lock. A centrally positioned single-hand grip releases the top from the windshield header or locks it in place.
• Top header becomes cover. Thanks to its 'parallel' folding sequence, the top's forward header remains upright as the top folds, and then serves as the cover for the folded top. This makes folding or raising the top essentially a 1-step process. The header covers the folded top and is flush wîth the body for a clean appearance.
• Easy operation. Gas-filled struts reduce the effort required to lower and raise the top.
• Heated glass rear window requires no periodic replacement and preserves rearward vision in cold or inclement weather.
• Aluminum and magnesium frame for low weight and inertia.
• Variable storage compartment. As in other open-body BMWs, the softtop compartment is adjustable for additional trunk space when the top is up.
Fully automatic power top. To lower the top, the user simply presses a button on the center console. The top unlatches electrically from the header and folds down. Raising the top is just as easy; both occur lightning-fast. The power top includes all the features of the standard one, plus –
• Interior lining for enhanced weather protection, reduced wind noise inside
• Choice of three colors.
The Coupe body/chassis structure:the ideal platform for razor-sharp handling
Reporting the Coupe's debut at the Geneva Automobile Salon, Switzerland's authoritative Automobil Revue described the design in its February 1, ‘06 issue: 'The Z Coupe embodies the new BMW design in its purest form. It is characterized by round, flowing lines. Curved, long hood, pronounced wheel arches and a 'trough' down the roof's center are classic sports-car design cues, but here they're newly mixed in the BMW way. The roof flows in an arc to the rear window and on to the vertical rear cutoff point.' America's Automobile (December ‘05) lent this note of opinion: 'There's no controversy over the way the forthcoming BMW Z4 Coupe looks. It's stunning, and it's heading to showrooms next summer.'
In its lower-body contours, the Coupe corresponds mostly to the Z4, wîth its refined front end and hood lines; long-hood, cabin-back proportions; and double beltline in profile view. In particular, the lower, stylistically primary beltline begins above the outer headlight, curves upward over the wheels and then downward into the door, and 'hikes' sharply upward again, finally heading downward to conclude at the rear edge. Because the Coupe's upper beltline has a visually longer continuity as it extends on past the rear-quarter window wîth its traditional BMW 'Hofmeister kink,' the lower one even more boldly evokes the fender line of classic Grand Touring coupes.
Even stronger in its aesthetic impact is the fastback roofline. For one thing, in cross-section its center depression or 'trough' is reminiscent of certain GT coupes of the Italian coachbuilder Zagato in the Fifties and later. In profile view, it flows in a line parallel to the side windows' top edge, then continues on down to meet a crisp, stand-out cutoff point that forms a rear spoiler. Then it concludes at the bumper as the bottom edge of a rear hatch.
This hatch, including the entire roof from the rear window's top edge to the bumper, opens wide and high to provide excellent access to a relatively roomy cargo area that can accommodate two golf bags.
A cabin for two
In its interior design, the Coupe adopts the primary design themes and materials of the Roadster 3.0si. BMW's 'High Performance' leather upholstery is standard; the seats, upper door-panel inserts, console-side kneepads and center armpad are in this leather and it is available in four color schemes: Saddle Brown, Black, Dream Red/Black and Beige. Brushed-aluminum trim highlights the dash and console; Poplar wood trim is available at no extra cost in Light or Dark tone. The Coupe features a cloth headliner, in Gray or Beige according to interior color scheme, and the A-pillar trim is also distinct from that of its Roadster counterpart. The available Extended Leather upholstery is described under Options.
As in the Roadster, sport seats, wîth prominent cushion and backrest side bolsters to support occupants during energetic driving, are standard. Their standard adjustment is 6-way manual; available in the Premium Package or as a stand-alone option is 8-way power adjustment, wîth memory for the driver's seat. M sport seats, also described under Options, are available in combination wîth the Sport Package.
The §teering wheel has manual tilt/telescopic adjustment. A contemporary instrument cluster, wîth white-on-gray analog speedometer and tachometer, includes LED indicators in the dial faces and between the dials; fuel and temperature gauges are set into the tachometer face.
Another amenity shared wîth the Roadster 3.0si is the Z4 Series' 10-speaker premium audio system, an AM/FM/CD/MP3-capable unit featuring –
• Audiophile-quality speakers throughout, including two 160-mm subwoofers incorporating Carver long-stroke technology
• A powerful Carver amplifier and 7-band Digital Sound Processing
• An FM reception-enhancing diversity antenna system.
Last year the Z4 Series became the first European cars to win the coveted THX Certification for their premium audio system. THX Ltd. was established in 1983 by filmmaker George Lucas, and has taken its mix of technology and certification programs to emerging entertainment media, including home theater systems, DVDs, video games and high-performance automotive audio systems. THX engineers worked closely wîth BMW to analyze Z4 models' cabin acoustics, speakers and other audio components to determine whether they perform to THX standards. ( posted on conceptcarz.com) They did; the result is a THX Certified Premium Sound System that is designed to deliver a music experience as the artist intended.
In the closed-body environment of the Coupe, this system promises even more enjoyable listening. It includes a reception-enhancing diversity antenna system, and an iPod adapter kit is available to broaden the range of audio inputs.
BMW's advanced N52 6-cylinder concept
Most vehicle manufacturers' 6-cylinder engines are in the V-6 format, whose compactness is advantageous for small or midsize cars wîth front-wheel drive. By contrast, BMW's inline 6-cylinder engines are brilliant for their smoothness and sound, and BMW customers as well as professional auto critics have come to treasure them for these attributes. BMW has retained this inline format while developing it toward reduced weight, more compact dimensions – and even more brilliant performance, smoothness and sound. An increase in fuel efficiency and even tighter control of emissions were also set as goals for the engine.
The result of this quest is a generation of 6-cylinder engines, called N52. Compared to its predecessor, the M54 engine family, the N52 achieves notable progress on all fronts (N52 3.0-liter of 3.0si models vs. previous M54 3.0-liter):
• Greater power, 255 hp vs. 225 hp – a very impressive 85 hp/liter.
• Greater torque, 220 lb-ft. vs. 214, and even stronger torque delivery across the broad range of engine speeds.
• Higher revving ability. The 'redline' is 7000 rpm, vs. 6500 for the M54.
• Superior fuel efficiency. Both 3.0si models (Roadster and Coupe) wîth automatic transmission are EPA-rated at 21 mpg city/30 mpg highway, up significantly from their 3.0i predecessor model's 19/27. With manual transmission, the 3.0si Roadster and Coupe essentially match their predecessor wîth 20/29 mpg vs. the previous 21/29.
• Reduced weight – 22 lb. less. Had BMW engineers evolved the previous engine to meet their goals, it would have weighed 52 lb. more than the N52 engine does.
• More compact – Because there is just one external drive belt, vs. the previous two, overall engine length is about an inch shorter.
Here's how this dramatic progress was achieved – over an engine that was already outstanding in every respect.
Valvetronic variable valve lift. This exclusive, patented innovation appears in the N52 in refined form.
Variable valve lift is a step beyond variable valve timing – which this and all other current BMW gasoline engines also have. Valvetronic varies lift to a far greater degree than other variable-lift systems; indeed, this concept varies lift so extensively that it replaces the traditional engine throttle; engine breathing is controlled by the valves rather than a throttle or throttles.
The Valvetronic mechanism sits atop the intake valves. Each of the engine's 24 valves is actuated as the camshaft lobe deflects a finger-type rocker arm. On the intake side, there is an additional element between the camshaft lobe and rocker arm, called an intermediate follower.
Úpon contact by the lobe, this follower actuates the rocker arm and, in turn, the valve. The follower is positioned by an eccentric shaft that a servo motor rotates in response to the driver's accelerator-pedal movements; the eccentrics on this shaft determine each intermediate follower's pivot point and thus varies the valve lift.
Here are the highlights of Valvetronic:
• Intake valves assume function of throttle. Engine breathing – air intake – is controlled by varying valve lift. The driver's foot gives the commands; valve lift varies accordingly. At minimum lift, the engine is idling or decelerating; at maximum lift, it delivers full power.
• Greater efficiency. As a throttle closes, it imposes a restriction that incoming air must snake around. This causes 'pumping losses,' which take a greater proportion of engine power at lower speeds. By eliminating the throttle , Valvetronic essentially eliminates pumping losses.
• More spontaneous engine response. Again, because there is no conventional throttle.
• More power. High valve lift contributes to high power output. With conventional valvegear, there's a limit to how high valve lift can go without degrading low-speed operation. With Valvetronic, lift is tailored precisely to all operating conditions, and is extra-high at the top end. The 3.0si engine's power peak (255 hp) comes at a relatively high 6600 rpm. Yet low- to medium-speed operation is not compromised.
• 'Fatter' torque curve. Not only does the N52 engine produce more torque than its predecessor; torque also peaks at a lower engine speed, 2750 rpm vs. the previous 3500 rpm. This means stronger low- to midrange response.
• More refined engine operation. Light-load operation is especially smooth because valve lift is low.
• Low friction, precision components. Every 'rubbing point' in the Valvetronic mechanism is not a rubbing (friction) point at all. Instead, low-friction rollers transmit the motion: from cam lobe to intermediate follower, follower to rocker arm, eccentric shaft to follower. The follower itself is a precision component in this higher-rpm evolution of Valvetronic. As before, zero valve clearance is maintained hydraulically to ensure quiet operation, though by a different mechanism.
How Valvetronic has evolved. As dramatic as these fundamental advantages of Valvetronic are, wîth the N52 engine they become even more significant. Though highly technical and detailed, the evolution of Valvetronic can be understood in these broad terms:
• Maximum engine speed increased by 500 rpm. This was enabled by making Valvetronic's reciprocating parts more rigid.
• Maximum intake-valve lift increased from 9.7 mm to 9.9 mm, which contributes to the increase in maximum power output.
• Greater maximum intake-valve acceleration. Less time is spent opening and closing the valves; thus they are effectively open longer, further reducing pumping losses.
• Phasing of the two intake valves. Starting from minimal intake-valve lift
(i.e., idling), an increase in engine load causes the lift and timing of intake valve 1 to increase faster than that of valve 2. At its maximum, this phasing has valve 1 lifting 1.8 mm more than valve 2; at about 6 mm, the two valves are again 'in synch.' This achieves an asymmetric distribution of the fuel/air mixture that enhances fuel economy under low-load driving conditions.
Improved combustion chambers. Subtle refinements to the combustion-chamber shape conspire wîth the intake-valve phasing to create more stable combustion, wîth benefits to fuel efficiency and emission control.
Further evolved VANOS. Double VANOS variable intake- and exhaust-valve timing is a familiar feature of all current BMW engines. The range over which intake-valve timing can be varied has been increased by 10°, achieving yet another de-throttling effect.
3-stage induction system. Previous Z4 engines had a 2-stage (or dual-resonance) system: one intake-path length for lower rpm, the other for higher rpm. This system further optimizes the engine's power delivery by providing an additional 'middle' stage. Electrically switched, the three stages are:
• Low-speed: idle-3250 rpm
• Medium-range: 3250-4500 rpm
• High-speed: 4500-7000 rpm.
(This feature is present only on the Z4 3.0si engine; the 3.0i engine has a single-stage intake manifold.)
Higher fuel-injection pressure, up from 3.5 to 5 bar (51.4 to 73.5 lb/sq in.), results in an improved injection spray, helping reduce raw hydrocarbon emissions in a cold engine.
Engine electronics. The number of variables (inputs) feeding into the engine's electronic management system has increased significantly; a completely new system was developed. Among many innovative details, the basic ignition and valve-timing functions are duplicated. The first part was optimized for fuel consumption and emissions; the second part was determined according to pure driving parameters. Depending upon how perfectly the engine is running at any time, control interpolates between the two strategies. Únder ideal conditions, the engine always runs wîth its lowest fuel consumption. In case of poor fuel quality or unfavorable environmental conditions, the control parameters prioritize driveability.
Magnesium/aluminum composite construction
Although the direct customer benefits of this unique and pioneering construction are subtler than those of Valvetronic, this is an important innovation – a world's first in modern times and exclusive to BMW.
Structurally, the N52 engine block consists of three major castings:
Bedplate (magnesium alloy ). This casting forms the lower portion of the block (crankcase), and is similar in concept to a construction element found in some racing engines – as well as the 500-hp V-10 engine that powers the BMW M5 and M6. The bedplate combines wîth the upper crankcase to form the outer shell of the cylinder block, resulting in an ultra-rigid engine structure.
Úpper crankcase (magnesium alloy). J oining the bedplate at the level of the crankshaft (main) bearings, this too is a weight-saving casting. It is mounted onto the bedplate from above.
Insert (aluminum alloy). Forms the cylinders and their coolant passages. Whereas the previous engine has an aluminum block wîth cast-iron sleeves as the cylinders' working surfaces, this insert is of silicon-impregnated aluminum (Alusil). Silicon particles are thus cast into the block; a 'soft honing' machine removes just enough of the aluminum to leave the crystals as the ultra-hard cylinder surfaces. In this sense, the N52's block construction resembles that of current BMW V-8 and V-12 engines, though these blocks are all-Alusil.
How it goes together. First, the aluminum insert is cast by conventional methods. Then, during a recently developed die-casting method, the magnesium upper shell shrinks onto the insert while cooling; structural rigidity and stability are ensured by interlocking ribs where the two castings meet.
In the next step, the upper crankcase, consisting of magnesium shell and aluminum insert, is mounted onto the magnesium bedplate from above. The sintered-steel main bearings' lower halves are in place in the bedplate, the upper halves in the upper crankcase. After the bedplate and upper crankcase have been bolted together, a liquid sealing compound is injected into a groove on the contact surface between the two components. Special aluminum bolts are used to attach parts, such as the engine mounting brackets, to the magnesium/aluminum castings.
As in all BMW engines for decades, the cylinder head is of aluminum; however, the head of an inline 6-cylinder engine must be cast wîth great precision because its relatively great length implies relatively large contraction as it cools after casting. The casting process used here is called 'lost-foam'; this process, which employs a polystyrene 'dummy' of the head to form the mold into which the aluminum is poured, results in an extremely precise casting.
Other weight-saving materials. Though the magnesium/aluminum composite crankcase construction is the most sensational example, other materials and production innovations also help pare weight from the N52 engine. The second most productive material innovation was the adoption of hollow camshafts, which save a remarkable 2.6 lb. Beginning as steel tubes, the camshafts are shaped in a hydroforming procedure, subjected from the inside to a water pressure of 4000 bar (58,000 lb./sq in.) against outer forms to achieve the cam profiles. All this takes place in a cold state – nothing melts – and as a final step the cams are polished to a finish quality of 1/1000 mm.
The engine's camshaft cover is of weight-saving magnesium. And the chain camshaft drive, a high-durability, low-maintenance feature of all current BMW engines, has an aluminum chain tensioner that also saves weight. Instead of being a separate casting, the camshaft drive's housing is integrally cast into the magnesium structure, eliminating a production step and sealing components. As one final weight-reducing element, the exhaust headers' flanges are formed from 2-mm-thick steel, significantly lighter than the 12-mm flanges used previously.
Electric water pump. A conventional engine water (coolant) pump is driven by a belt at a speed directly proportional to engine rpm. This innovation is electrically driven and electronically controlled according to the engine's coolant and oil temperatures at any moment. Thus it runs only as much as needed, and in doing so consumes a maximum of 200 watts vs. up to 2 kilowatts (10 times as much) for a conventional pump. The electric pump has numerous tangible benefits:
• By requiring less power, contributes to the engine's increased power output.
• Faster engine warmup, because it doesn't circulate coolant when the engine is cold.
• By eliminating an external drive belt, makes the engine shorter.
Variable-volume oil pump. Conventional oil pumps, too, deliver oil in direct proportion to engine speed. To supply pressure to the VANOS system (which employs oil pressure to rotate the camshafts and thus vary valve timing) at all speeds and temperatures without excess capacity at high engine speeds, BMW engineers developed a new type of oil pump. By varying the output of its pump element according to engine oil pressure, this pump always delivers sufficient pressure to lubricate the engine and operate VANOS, yet never pumps more oil than is necessary. Thus it –
• Contributes to the engine's increased power output, by requiring less power from the engine.
• Doesn't require a bypass to divert excess flow, which can be up to 80% wîth a conventional pump. This also avoids possible excess oil temperatures and oil foaming.
Oil/coolant heat exchanger. Another feature that speeds engine warmup; during this phase of operation, it transfers heat from the coolant to the oil circuit. Únder conditions of high engine power and high oil temperatures, it performs the reverse, transferring heat from the oil circuit to the coolant, from which the engine cooling system then removes excess heat.
Transmissions: all choices are 6-speeds
The previous Z4 2.5i had a 5-speed manual transmission, the 3.0i model a 6-speed. For '07, all Z4 models come standard wîth a 6-speed like the one Motor Trend praised in its August '04 issue: 'Like the engine,' commented the magazine, 'the gearbox is a sweetheart. Said one editor, ‘The shifter has that positive, spring-loaded feel.' Another wrote, ‘It snicks into its gates wîth an oiled authority.''
There's also good news for those who like their shifting automated – at least part of the time. Last year, the Z4 joined the other BMW Series in offering a 6-speed automatic; compared to the previous 5-speed it's fully 10% lighter, has a more efficient torque converter and new shift programming for improved responsiveness, actually operates wîth fewer internal clutches, and can reduce fuel consumption, particularly at cruising speeds when 6th gear is in frequent use.
As wîth other current BMW automatics, the STEPTRONIC feature offers drivers a choice of Normal, Sport and Manual modes. The Sport mode, in which shifts occur at higher engine speeds, is engaged by moving the lever leftward from Drive; the Manual mode is engaged when the driver manually chooses a gear by tipping the lever forward (for downshifts) or rearward (for upshifts).
In the Z4 models, this transmission has two further features, both conducive to sporty driving:
• Shift paddles on §teering wheel. Analogous to the shift lever, pulling the paddle(s) toward the driver produces an upshift; pushing forward gets a downshift.
• Direct Selection of Manual mode. If, while driving in D, the driver manually downshifts via paddle or shift lever, the Manual mode engages. But if the driver makes no further manual shifts within 15 seconds, the transmission returns to automatic operation.
Z4 Coupe structure: 'solid lightweight'
The Coupe's basis is of course the Z4 Roadster, whose outstanding handling is due in part to a structure that is outstandingly rigid for an open-bodied vehicle. From this solid basis, the Coupe gains additional rigidity from its fixed roof; at 32,000 Newton-meters per degree of body twist, the Z4 Coupe delivers that tight, firm handling feel that is a traditional hallmark of compact GT coupes; yet its additional weight over the Roadster is a mere 22 pounds.
To achieve such results, the Coupe retains the Roadster's weight-reducing, strength-enhancing features:
• Aluminum hood
• Y-form front longitudinal structural members
• Side sills designed to achieve maximum rigidity within acceptable bulk
• An underbody that spreads strength evenly over its entire length and width
• Thrust plates at the suspension attachment points: aluminum in front, steel at the rear (this juxtaposition of materials also enhances weight distribution)
• A V-shaped brace that adds further rigidity to the rear suspension subframe's attachment points
• Reinforcing braces running from the front suspension's strut towers to the cowl area; these can be seen by opening the hood.
Suspension that's firmly planted on the road
Z4 front and rear suspension systems are evolutions of the technology that has given BMW's M3s their award-winning road capabilities. At the front, this means that the Z4 strut-type front suspension features –
• Forged aluminum lower arms to reduce unsprung weight and thus improve ride and handling on rough road surfaces.
• Hollow strut rods for a 10% weight savings in these components.
• Evolved geometry – large positive caster to improve straight-line stability.
• Wide track.
This system is simpler than the double-pivot type found in 3 Series Sedans and Sports Wagon and the 5 and 7 Series.
At the rear is a multi-link system, also similar to what's found in the M3s and capable of keeping the rear wheels at virtually ideal angles relative to the road. With the proven capabilities of these suspension systems, every Z4 has the 'right stuff' for awesome handling. To underscore its sports-car character, relatively firm springs, shock absorbers and anti-roll bars are used, meaning –
• Stable and predictable handling - for example, changing direction very little when the driver lets off the accelerator while cornering.
• A firm ride, communicating that the Z4 is a serious sports car.
• Flat cornering, achieved via a low center of gravity and the firm suspension calibration.
• Specific Coupe calibration. BMW's suspension engineers have calibrated the overall suspension system – spring, shock-absorber and anti-roll-bar characteristics – to the Coupe's increased rigidity. The Roadsters themselves had already been newly optimized in May ‘05, so the entire Z4 Series enjoys freshened road competence.
• Impressive cornering ability: Road & Track (March ‘05) recorded a 0.92g figure for the Z4 Roadster 3.0i wîth Sport Package.
The Valvetronic engine' response characteristics do their part too: a compromise between spontaneous reactions to the accelerator pedal and smooth power-on/power-off transitions.
Electric Power Steering: §teering wîth Z4-specific benefits
Úniquely among BMWs, Z4 §teering is assisted by an electric servo motor instead of a conventional hydraulic pump. Benefits of this feature, all important to sport-minded drivers, include these:
• Facilitates specific tuning of §teering characteristics.
• Vehicle-speed-sensitive power assist (Servotronic). Other current BMW models wîth vehicle-speed-sensitive power assist are the 5, 6 and 7 Series. Its primary benefit is reduced §teering effort in parking and at very low speeds.
• Reduced vehicle fuel consumption, because the electric motor operates only when the §teering wheel is turned. A conventional hydraulic pump runs all the time.
The Coupe benefits from the same enhanced braking system as on the Roadster 3.0si:
• Front brakes – 325-mm/12.8-in. diameter, up from 300/11.8 on the previous Z4 Roadster 3.0i
• Rear brakes – unchanged at 294-mm/11.6-in. diameter.
The brake rotors are ventilated all around.
Run-flat tires, sporty wheels:
beefy running gear, 17- or 18-in.
The Coupe shares the Roadster 3.0si's wheel and tire three lines sizing and speed ratings, but adopts a distinctive wheel design for its optional Sport Package. The particulars:
• Standard – 17 x 8.0 wheels all around; the 10-spoke Turbine design is shared wîth the 3.0i Roadster. Tires are 225/45R-17 performance rubber wîth a W speed rating .
• Sport Package – Sized 18x 8.0 front/18 x 8.5 rear, these wheels feature the Star Spoke design wîth five ribbed spokes. They wear 225/40R-18 front / 255/35R-18 rear W-rated performance tires5.
All Z4s come exclusively wîth run-flat tires, which obviate any need for roadside tire changes or a spare. Úser convenience and cargo space benefit.
Dynamic Stability Control: remarkable braking functions
All current BMW models have Dynamic Stability Control, which provides a wide range of traction and stability functions. Like the latest 3 and 5 Series models, Z4s come wîth an enhanced DSC system that adds driver-relevant braking functions for safer and more pleasant driving. They are:
• Brake Fade Compensation. When brakes heat up and fade under hard use, a given degree of deceleration requires more pressure on the brake pedal. As brake temperature rises, Fade Compensation automatically increases the hydraulic pressure in the brake system relative to pedal application, so the driver does not have to press harder on the pedal.
• Brake Standby. When the driver lifts off the accelerator pedal abruptly, DSC detects that sharp braking may be about to occur and applies just enough pressure in the brake system to snug up the pads against the rotors. By the time the driver's foot reaches the brake pedal, the short time lag normally resulting from bringing the pad to the rotor has been eliminated. The reduced stopping or deceleration distance could reduce the likelihood of an accident.
• Brake Drying. Acting on input from the rain sensor (an element of the rain-sensing windshield wipers), the pads are periodically brought up to the rotors – just enough to eliminate any film of water between pads and rotors, but not enough to cause any brake application.
• Start-off Assistant. Keeps the vehicle from rolling back when stopped facing uphill. The driver can then start up without doing a ballet wîth the clutch, brake and accelerator (manual transmission) or doesn't have to hold the accelerator or brakes while stopped on a hill (automatic transmission).
• Modulated ABS function. Thanks to 'analogized' control of the DSC brake valves, the anti-lockup function (ABS) is smoother. Instead of simply being fully applied and released, the application and release of these valves are modulated.
The selection of factory options and BMW center-installed accessories for the Z4 Coupe 3.0si corresponds mostly wîth that for the Roadsters, except of course for such offerings as a removable hardtop or power softtop.
Premium Package. Combines luxury and convenience features plus BMW Assist, a system of customer services and in-car telematics. Its contents are:
• Xenon headlights wîth auto-leveling and luminous rings (Coupe only)
• Auto-dimming interior and exterior mirrors
• 8-way power sport seats wîth driver's-seat memory
• Storage package – elastic net on the right side of the center console and on the back of each seat.
• BMW Assist, wîth 4-year subscription
• Automatic power softtop
• 4-function onboard computer
• Automatic climate control wîth micro-filter ventilation and automatic recirculation control
Sport Package. Includes –
• Dynamic Driving Control. A Sport button on the console selects quicker throttle action, reduced power-§teering assist and (if the vehicle is so equipped) an additional Sport mode for the STEPTRONIC automatic transmission. (posted on conceptcarz.com)
• Sport suspension. Lowers the vehicle by 15 mm/0.6 in. and firms up the springs, shock absorbers and anti-roll bars.
• 18 x 8.0 front/18 x 8.5 rear Star Spoke wheels; 225/40R-18 front / 255/35R-18 rear W-rated run-flat performance tires5 (3.0si models only – 3.0i: 17 in. mixed-size wheels and tires)
6-speed STEPTRONIC automatic transmission. (posted on conceptcarz.com) The 6-speed automatic improves responsiveness and performance by spacing its ratios closer than previous Z4s'
5-speed; makes highway cruising quieter and potentially more fuel-efficient; and includes §teering-wheel shift paddles as well as Direct Selection of the Manual mode.
Xenon headlights, also available as a stand-alone option.
Headlight cleaning system. Greatly appreciated in inclement weather; employs nozzles that are retracted into the front bumper when not in use.
Metallic paint. Seven metallic colors and three non-metallics are offered. As always wîth BMWs, many of the colors are fascinating and elegant.
BMW On-board Navigation System wîth DVD database. The system's display is housed in a pop-up pod at dash center; in addition to GPS Navigation, On-board Computer and other functions, it also assumes the role of audio-system display. When the radio is switched on, the Navigation monitor automatically rises into its operating position.
Extended Leather upholstery. This most luxurious Z4 interior includes many distinctions from the standard leather treatment:
• Higher-grade leather on seats and head restraints
• This same leather on an expanded area of the door panels
• Leather-trimmed windshield frame and sun visors
• Premium galvanic trim on automatic-transmission shift paddles, gearshift-boot surround, shift knob, inside door handles and door pulls.
Wood interior trim. Light or Dark Poplar Grain trim is available at no extra cost. It consists of a large dash panel and console trim.
Power seats wîth driver's-seat memory. Besides being part of the Premium Package, the 8-way power seats are available as a stand-alone option.
M sport seats. These optional seats offer enhanced seating comfort and lateral support via –
• More aggressive side bolsters, particularly at the backrests' upper edges
• Adjustable thigh support
• Adjustable cushion angle (adjustable cushion height is standard).
This option requires the Sport Package. When also combined wîth the power seats, they include 8-way power adjustments; otherwise they are manual. The thigh-support adjustment is always manual.
Heated seats. 3-stage, thermostatically controlled heating provides a wide range of adjustability and steady heat under changing temperature conditions.