BMW 3 Series suspension technology highlights
More driving fun in the medium class car segment: It was under this premise that, in 1975, BMW presented an entirely new concept. With the BMW 3 Series brand-typical virtues such as dynamics and agility became factors of success in this segment for the very first time. The sporty saloon's unique handling characteristics convinced right from the word go.
The unmistakable character of the BMW 3 Series was the result of a consistently implemented basic concept: high-performance engines were complemented by power transfer to the rear wheels, even load distribution and an advanced chassis construction. As early as1975, the technically sophisticated wheel suspension, remarkably precise, torque steer-free steering and powerful brakes guaranteed the driver of a BMW 3 Series car exceptionally sporty and safe vehicle handling in any situation. A standard still applicable to this very day. Even if every single component of the suspension technology has been subject to a remarkable development process over the past 33 years, the basic concept of driving pleasure does indeed remain in existence to this very day. Thanks to the most modern suspension system in its segment, the BMW 3 Series today still sets the benchmark in sportiness and agile handling.
1975: Premiere of the BMW 3 Series - performance and suspension at luxury class level.
The new series was launched in 1975, comprising the BMW 316, the BMW 318, the BMW 320 and the BMW 320i and four engine variants. With its 98 bhp four-cylinder engine even the BMW 318 almost entered the domain of triple-digit performance values then predominantly reserved only to luxury class vehicles. However, in terms of suspension technology, all versions of the BMW 3 Series already surpassed normal standards typical of their respective segment. They were also a match for pure sports cars. The sports suspension featured by the first model generation had wheels individually suspended on transverse arms with spring struts at the front and likewise, at the rear, independent wheel suspension with semi-trailing arms and spring struts. This combination facilitated the harmonisation of an above-average driving dynamics potential with a high degree of comfort.
The transverse arms on the front axle were guided by stabilisers according to the McPherson principle, the new front axle construction offering ideal preconditions for high steering precision. Also, with the BMW 3 Series an entirely new design feature made its debut at BMW - the flexibly mounted rack-and-pinion steering. The steering column now comprised the following components: steering shaft, cardan joint and flexible discs.
Better performance, enhanced technology: disc brakes all round and optional servo steering for the six-cylinder versions.
The BMW 3 Series of the first generation came with 13-inch steel rims as standard. Alloys of the same size were available as an option. Thanks to disc brakes on the front wheels and drum brakes at the rear, excellent deceleration values were achieved from the word go. However, with the introduction to the BMW 3 Series of the exceptionally powerful six-cylinder power units, it became necessary to employ brakes that were even more effective. Consequently, the BMW 323i, the series' top-of-the-range model launched in 1977 and delivering 105 kW/143 bhp, was also equipped with disc brakes on the rear wheels. Moreover, as in the case of the BMW 320/6, the steering could be optionally fitted with hydraulic power steering technology.
1982: The second generation - even more agile, even safer.
1982 saw the arrival of the second generation of the BMW 3 Series, a worthy successor to the trendsetter and bestseller. The new model reflected advancement and variety in every aspect - new design, optimised aerodynamics, increased space and comfort, higher power output, additional body and engine variants. For example, during its lifespan a four-door version, the first BMW 3 Series Touring, the Convertible and the BMW M3 sports car were introduced. Furthermore, diesel engines and four-wheel drive were added to the BMW 3 Series portfolio. This strategy was most successful. With more than 2.3 million units sold, its predecessor's sales figures were topped by a million vehicles.
In terms of agility, driving safety and handling precision the second generation of the BMW 3 Series also outshone all competitors in its segment. Engineers had modified the front axle of the new BMW 3 Series in order to increase active safety even further, without affecting the typical handling characteristics. At the front, the new 3 Series featured a single-joint spring strut suspension with sickle-shaped transverse control arms and a reduced rolling radius to minimise the negative forces that affect steering.
The rear axle now incorporated semi-trailing arms with separate dampers and springs. The newly designed barrel springs with progressive spring characteristics provided enhanced comfort, particularly on slightly uneven road surfaces, and thanks to their compact design they also facilitated an increase in boot capacity. The linkage of the rear semi-trailing arms now had a sweep of only 15 degrees instead of 20.
Furthermore, the track, now widened by 35 millimetres, the low weight and reduced aerodynamic resistance had a positive effect on the driving characteristics of the new BMW 3 Series. At the time of its launch, there was a choice of the two four-cylinder models BMW 316 (66 kW/90 bhp) and BMW 318i (77 kW/105 bhp) as well as the two six-cylinder versions BMW 320i (92 kW/125 bhp) and BMW 323i (102 kW/139 bhp). A sports suspension was optionally available from factory for all four versions. Also, alloy wheels were on offer as an alternative to the standard 14-inch steel rims. The wheels, which were larger compared to those featured on the predecessor model, offered sufficient room for larger dimensioned brakes. New floating-calliper brakes replaced the previously employed fixed-calliper design and a larger brake power assist unit was added. The BMW 323i was once again fitted with disc brakes all round. The front disc brakes were - as on the BMW 320i - ventilated.
Improved stability thanks to ABS and four-wheel drive.
For the first time, an optional electronic anti-lock brake system (ABS) was available for the six-cylinder versions. Initially, BMW had employed this innovative safety feature on the BMW 7 Series, but only a short while later the premium technology was utilised for the high-output versions BMW 323i and BMW 320i. Sensors for wheel speed, a control unit and a hydraulic unit automatically controlled wheel slip and wheel acceleration in such a way as to prevent the wheels from locking in hazardous situations. This also ensured that both stability and steerability were maintained when the brakes were applied, even on slippery surfaces and in bends. From 1992, this feature was standard on all BMW 3 Series models.
The modified rack-and-pinion steering provided better tractability and increased precision on uneven road surfaces. The power steering technology already employed on the six-cylinder versions of the predecessors was now available for all models as an option.
In the year 1985, the top-of-the-range model was toppled from its leading position by the 126 kW/171 bhp six-cylinder model BMW 325i, which then already featured ABS as standard. At the same time the BMW 325iX, the version with the best traction and four-wheel drive, was launched. Right from the start, BMW engineers were not satisfied with simply an on-demand front-wheel drive. In fact the transfer gearbox with automatic viscous locks permitted ABS-compatible and permanent four-wheel drive. This resulted in optimised traction in all road conditions and the highest degree of stability in every motoring situation. In normal operation 63 percent of power was transferred to the rear axle and 37 percent to the front. So power transmission had very little effect on the steering. Hence the BMW 325iX convinced through exceptionally harmonious driving behaviour.
Inspired by motor sports, geared to performance: the BMW M3.
Finally, at the 1985 International Motor Show in Frankfurt, the spotlight focused on a further newcomer that set the pulse of many a motor sports enthusiast racing - the first BMW M3. Developed on the basis of the two-door BMW 3 Series Saloon and powered by a 147 kW/200 bhp four-cylinder engine, an uncompromising sports car had entered the scene. The first chapter of an unrivalled success story, that has lasted to this day, had been written.
Not only was the BMW M3's power unit inspired by motor sports, but also its suspension technology. For instance, axle kinematics, springs and dampers were extensively modified and adapted to racing standards and to the high engine performance. The brake system with ABS as standard comprised internally ventilated brake discs at the front and an engine-driven high pressure pump. This servo pump simultaneously supplied power to the steering, so that both systems operated independently from negative engine pressure.
In the model year 1987, the M3 was also the first BMW to offer electrically adjustable dampers. The driver could choose between "Sport", "Normal" and "Comfort" using a rotary switch located next to the handbrake lever. Control lamps on the dashboard indicated which setting had been selected.
1990: The third generation of the BMW 3 Series - more agility, enhanced precision and electronic slip control.
The third BMW 3 Series generation made its first appearance in October 1990, featuring boldly elongated contours and thoroughly revised technology. At the time of its launch a choice of two four-cylinder and two six-cylinder versions was made available. The BMW 316i served as an entry version with an output of 74 kW/100 bhp, the BMW 318i delivering 83 kW/113 bhp, and the two straight six-cylinder versions featured in the BMW 320i and the 325i mustered 110 kW/150 bhp and 141 kW/192 bhp respectively. The long 2,700-millimetre wheelbase and the elongated body made a promise of sheer driving pleasure and the chassis also came well up to expectations.
The third generation of the BMW 3 Series ran on a single-joint spring strut axle with transverse stabilisers at the front, and now featured a rear axle with a central control arm and two transverse control arms arranged on top of each other for optimised stability particularly in bends, harmonious running characteristics and enhanced suspension comfort.
Both front and the rear axles were fitted with double-pipe gas pressure dampers. For the first time engineers had designed the rear track to be wider than at the front. This structural design remained in use for the model generations that followed.
Power assisted steering for the even further developed rack-and-pinion steering was now a standard feature on the BMW 318i. For the first time the driver was not only able to adjust the seats individually, but also adjust the steering column axially in order to find his or her ideal position behind the wheel.
An M technology sports suspension lowered by15 millimetres was available as an option. The wheels, either steel or light-alloy, depending on the model, had increased in size to 15 inches. The effectiveness of the brakes was also increased even further. The four-cylinder models featured disc brakes at the front combined with drum brakes on the rear wheels, the six-cylinder versions being fitted with disc brakes all round, including internally ventilated discs at the front.
The top-of-the-range model, the BMW 325i, came with ABS as standard, further versions offering this state-of-the-art system initially as an option and, as from 1992, as a standard feature. In addition, Automatic Stability Control (ASC) was included in the range of optional equipment. Irrespective of the driver's accelerator pedal input, the anti-slip control system permitted only a limited amount of engine power to be conveyed to the drive wheels in each respective driving situation to prevent the wheels from spinning. From 1997, the enhanced form of this technology termed ASC+T, with additional braking intervention for stability, was available for all BMW 3 Series models.
The new edition of the BMW M3, which was based on the BMW 3 Series Coupe and launched in 1992, also impressed with further enhanced dynamics resulting from the newly developed 3-litre straight six-cylinder power unit with an output of 210 kW/286 bhp as well as an entirely re-engineered suspension. The single-joint spring strut front axle was complemented with reinforced spring seats and axle stubs. And the new central-arm rear axle was, inter alia, adapted to the high engine output through the addition of modified longitudinal arms. Furthermore, dampers and stabilisers were now significantly firmer. These modifications were also reflected in the body height: The BMW M3 was precisely 31 millimetres lower than a BMW 3 Series Coupe. The so-called compound brakes at the front were a further highlight. Due to the compound construction comprising an aluminium brake-disc chamber and a grey cast iron friction ring, the disc was able to expand without distorting as the brakes were applied. Thanks to its dynamic and superior handling characteristics, the new BMW M3 set standards internationally in terms of sportive driving pleasure. Hence it was, for example, voted "Best Handling Car" by experts from the US car magazine "Car and Driver".
1998: The fourth generation with a consistent lightweight construction and innovative stability control systems.
BMW developed a newly conceived lightweight suspension and innovative stability control systems for the fourth generation of the BMW 3 Series. With its basic construction and its technical highlights, the suspension technology reached a level previously only found on luxury class automobiles. The proportion of aluminium used on the suspension was now around 60 kilograms, i.e. 20 percent of the overall weight. Moreover, a further optimisation was achieved through the selective use of high-strength steel on front and rear axle supports. The overall construction was significantly lighter than that of the previous model and facilitated a further increase in agility. In addition to the distinctively increased body stiffness, the familiar even axle load distribution contributed towards the harmonious, stable and constantly controllable handling characteristics of the BMW 3 Series.
The fourth BMW 3 Series generation had a 25 mm longer wheelbase and a 60 mm wider track than its predecessor. The elongated body contours distinctively reflected the saloon's sporting character, driving dynamics even directly benefiting from its further reduced aerodynamic resistance. With regard to kinematics and elasto-kinematics, the central-arm rear axle with double-pipe gas damper and stabiliser corresponded to the construction of the previous model.
The use of high-strength steel for the rear axle improved vibrational behaviour, and a double-elastic rear suspension with rubber mountings provided additional comfort. In addition, the well-proven concept of a single-joint spring strut suspension with transverse stabilisers at the front was developed even further and complemented, inter alia, with a hydraulically damped transverse arm mount.
With the exception of the BMW 328i, which featured 16-inch alloys as standard, all variants of the fourth BMW 3 Series generation stood on 15-inch rims. During the years that followed a variety of light-alloy rims in various sizes up to 18 inches were available as an option. As in the case of the predecessor, power assisted steering was again included in the list of standard features and, for the first time, the steering column could not only be adjusted axially, but also in height.
Premiere for groundbreaking stability control systems: CBC and DSC.
Once again, a significant advancement had been achieved with regard to brake and stability control systems. All fourth-generation BMW 3 Series models were fitted with disc brakes all round. Their degree of effectiveness was optimised by ABS, which was now also a standard feature. BMW also introduced the Cornering Brake Control system (CBC), a further development of ABS and a technology that facilitated optimal utilisation of the rear axle braking force, but without having an adverse effect on tracking stability. It is the also task of the system used on current BMW models to counteract the vehicle's tendency to drift inwards if the brakes are applied when driving round bends at high speeds. CBC identifies the situation and ensures that the vehicle is stabilised by means of a controlled build-up of braking force to each individual wheel. This counteracts the tendency to oversteer.
Likewise, the anti-slip control system ASC + T was again included in the range of standard features on all BMW 3 Series vehicles. Dynamic Stability Control (DSC) was a brand new technology initially only available for the 328i as an option. This innovative system was designed to rapidly and accurately identify any possible adverse effects on the vehicle's stability by measuring the yaw rate and lateral acceleration and to prevent oversteer or understeer particularly in bends by means of appropriate intervention. In this way it became possible to re-establish vehicle stability by means of targeted brake intervention on individual wheels as well as through a reduction in engine power. DSC has been a standard feature on all BMW 3 Series models since 2001.
As early as 2000 it was possible to equip both the 3 Series Saloon and the 3 Series Touring with the new version of BMW four-wheel drive technology. Permanent power transmission to all four wheels was linked to the Dynamic Stability Control system. In this manner it was possible to achieve a traction-enhancing locking effect by means of brake intervention on each individual wheel. The new all-wheel technology was offered in combination with six-cylinder engines. There was a choice of the variants 330xi, BMW 325xi and BMW 330xd.
New BMW M3 with variable M differential lock.
The optimisation of the suspension system featured on the new generation of BMW M3s - again developed on the basis of the BMW 3 Series Coupe and presented in 2000 - also managed to keep pace with technical advancement in the field of drive technology. The BMW M3's new straight-six cylinder engine now delivered 252 kW/343 bhp, and thanks to high engine speeds and a comparably short axle transmission, it developed enormous power that had to be safely and consistently converted into driving dynamics.
The high-performance sports car profited from the exceptionally stiff body structure of the BMW 3 Series, its even axle load distribution and the weight-optimised suspension construction. In addition to individual suspension components, both the compound brake system and the effect of the Dynamic Stability Control system (DSC) were adapted to match the outstanding performance of the high-revving power unit.
Furthermore, the new version of the torque-sensitive differential lock system already employed on previous models offered improved traction in the event of the vehicle being driven in a demanding fashion. The variable M differential lock responded exceedingly sensitively to the varying friction values on the drive wheels. Depending on the driving situation, a variable locking value of between 0 and 100 percent could be produced. This ensured consistent optimum traction under all load requirements, irrespective of the road surface.
2005: The fifth generation - with the best suspension in its segment.
With the market launch of the fifth model generation 30 years after its success story had begun, the BMW 3 Series celebrated a spectacular anniversary in 2005. BMW engineers had been successful in again bringing the suspension technology a noticeable step forward, virtually bringing it in line with the characteristics of the drivetrain and car body. This resulted in better agility and more driving fun for the customer.
Thanks to a convincing and harmonious concept, the BMW 3 Series was able to further strengthen its profile within its segment. The new symbiosis of powerful engines, dynamic and cultivated driving characteristics, the distinctive styling with the typical BMW design language, a torsionally stiff, generously dimensioned body and innovative equipment features was a huge international success right from the word go. Just a year after the market launch, the new BMW 3 Series was awarded the title "World Car of the Year" in New York.
Current BMW 3 Series models boast the largest and most varied range of engines ever made available for the series. There is a choice of five petrol and five diesel engines, both for the Saloon and the Touring model. Four petrol and four diesel engines are available for the BMW 3 Series Coupe, whilst the BMW 3 Series Convertible comes in four petrol and three diesel versions. Output ranges from 105 kW/143 bhp for the BMW 318i to 225 kW/306 bhp for the BMW 335i. All-wheel drive - known as BMW xDrive technology with electronically controlled, variable power distribution between front and rear wheels for enhancing stability, traction and driving dynamics - is available for the Saloon, the Touring and, now for the first time, the Coupe.
Innovative axle designs.
The fifth BMW 3 Series generation also has a larger chassis than its predecessor. The wheelbase has increased by 35 mm and track width by 29 mm. Depending on the model version, equipment and loading condition, the load on the rear axle is between 48 and 56 percent, this being practically the ideal value for even weight distribution.
The design of the front axle has once again been derived from technology developed for the luxury class. The constructional concept comprising an axle with double-joint tension rod and spring struts corresponds to the principle used for the BMW 5 Series. Tension rods, transverse control arms, swivel bearings and front axle support are made entirely of aluminium, a lightweight concept with which BMW has made a particularly consistent advancement. A high degree of stiffness and weight optimisation are combined in a unique manner. Both characteristics have a positive effect on the vehicle's agility.
The five-link rear axle featured by the BMW 3 Series has been completely redesigned. The unique construction offers ideal preconditions for a particularly dynamic behaviour. With five individual control arms for each wheel, virtual kinematic points can to a large extent be freely determined. The large supporting base for track and camber on the wheel carrier side, extremely rigid control arms, the stiff rear axle support and the connection to the car body via pushrods facilitate elasto-kinematics that provide across a broad spring travel range precisely the wheel control necessary for superior vehicle handling in any situation. Furthermore, due to small and effective lever arms, the rear axle is hardly affected by negative influences and facilitates outstanding rolling characteristics. In addition, a well-balanced coordination of springs and dampers enhances the BMW 3 Series' agile character.
Depending on the model variant, the BMW 3 Series comes with 16-inch or 17-inch wheels as standard. The tyres have emergency running properties - likewise a standard feature and unique in this segment - that allow the journey to be continued even in the event of a total pressure loss. A tyre defect indicator notifies the driver as soon as the pressure loss in a tyre exceeds 30 percent. Disc brakes all round and ABS with the CBC Cornering Brake Control system are standard features.
All BMW 3 Series variants are fitted with internally ventilated discs at the front, six-cylinder versions and the BMW 320d additionally at the rear. Apart from the high degree of effectiveness, a weight-optimised construction was taken into account when developing the brake system. The continuous brake lining wear indicator, that also calculates the remaining mileage, also enhances safety and comfort.
State-of-the-art vehicle stability control with new functions.
The Dynamic Stability Control feature for the fifth-generation BMW 3 Series now has a significantly broader functional range. The stabilising effect achieved by means of brake intervention on each individual wheel and a reduction of engine power has been complemented by numerous other possibilities of enhancing safety and comfort in demanding driving situations. These include Automatic Stability Control (ASC), trailer stability control and Dynamic Brake Control (DBC), which automatically maximises brake force on both axles should it detect that the driver wishes to brake as hard as possible. Moreover, the special mode Dynamic Traction Control (DTC) can be selected at the push of a button, a feature that raises the response threshold of the DSC system. This facilitates better starting off on snow or loose sand and renders possible particularly sporty driving behaviour and high lateral acceleration levels in bends.
The DSC system featured in BMW 3 Series six-cylinder models also includes additional functions. By means of a systematic increase in brake pressure, the decrease in stopping power known as fading is prevented in the event of exceptionally high brake temperatures. Regular dry braking optimises brake performance in wet weather. With the brake readiness function moderate brake pressure is built up as soon as the driver takes his foot off the accelerator pedal. This guarantees spontaneous brake response. Furthermore, a hill-start assistant facilitates easier hill starts by preventing the vehicle from rolling backwards for a defined period of time.
Steering: Precise, efficient and more dynamic thanks to Active Steering.
Typical BMW characteristics such as driving pleasure, driving comfort and driving safety owe their existence to a considerable extent to the targeted precision of the steering and the accurate response given to the driver. With the exception of the BMW 335i and the BMW 335d, which are equipped with rack-and-pinion steering with hydraulic power steering technology, all BMW 3 Series variants feature electro-mechanical steering EPS (Electric Power Steering), which also includes the speed-dependent Servotronic steering assistance system.
EPS features a steering assistant which operates by means of an electrical actuator that can be utilised when required. The steering assistance system is only activated if it becomes necessary or if the driver wishes. During constant travel straight ahead the electrical actuator has no output. Hence EPS, an integral part of the BMW EfficientDynamics programme, is making a contribution towards a further reduction in the BMW 3 Series' consumption and emission levels.
Active Steering, which is optionally available for the BMW 3 Series, provides enhanced precision and steering comfort. In addition to the steering assistance system or Servotronic respectively, Active Steering varies the steering ratio according to driving speed. At low speeds a larger steering angle is effectuated than at higher speeds, but with the same amount of steering wheel movement. Consequently, less effort is required when parking the vehicle, for example. Within the medium speed range Active Steering enhances the BMW 3 Series' agile character. In contrast, at higher speeds it aids directional stability. Additionally, Active Steering adopts a stabilising effect in particularly demanding driving situations. In the event of braking manoeuvres on uneven surfaces (µ-split braking), the directional stability is maintained through targeted and restrained counter-steer.