Why Upgrading the E39 M5's Suspension Matters

The BMW E39 M5 remains one of the most celebrated sports sedans ever built, blending a naturally aspirated V8 with a chassis that rewards confident driving. While the factory setup was impressive for its era, two decades of engineering progress mean that modern suspension components can unlock significantly more performance. Upgrading sway bars, strut braces, and paying close attention to alignment transforms the M5 from a fast grand tourer into a precise cornering tool. These modifications also improve safety by reducing body roll and maintaining tire contact during emergency maneuvers. Whether you are tracking your car or simply enjoying a back road, addressing these three areas yields measurable, repeatable improvements.

The E39 M5's Factory Setup

From the factory, the E39 M5 arrived with a refined multi-link suspension, relatively soft bushings, and sway bars designed for a balance of comfort and capability. The chassis, while stiff for its time, still flexes under hard cornering, especially in the front strut towers. The original sway bars are hollow and around 25 mm front and 20 mm rear, leaving room for thicker, stiffer replacements. Alignment specifications were conservative, prioritizing tire wear and highway stability over ultimate cornering grip. Recognizing these baseline limitations is the first step in building a better-handling M5.

Signs Your M5 Needs an Upgrade

Common symptoms that your E39 M5 would benefit from suspension upgrades include excessive body roll in corners, vague steering response, front-end shudder over uneven pavement, and uneven tire wear on the inner edges. Worn factory bushings and aged strut mounts exacerbate these issues. If you find yourself making steering corrections mid-corner or feeling the car's weight shift unpredictably, sway bars, strut braces, and a proper alignment will bring clarity and control back to the driving experience.

Sway Bars – The Foundation of Cornering Control

Sway bars, also known as anti-roll bars, are torsion springs that connect the left and right sides of the suspension. Their job is to resist body roll during cornering by transferring load from the inside wheel to the outside wheel. Upgrading the sway bars on an E39 M5 is one of the most effective ways to improve transient response and cornering stability without sacrificing ride quality as much as spring or damper changes might.

How Sway Bars Work

When you turn the steering wheel, centrifugal force pushes the car's weight to the outside. The sway bar twists as the inside suspension extends and the outside compresses. A stiffer bar resists this twist more aggressively, keeping the car flatter. The result is more consistent camber alignment through the corner, better tire contact, and increased driver confidence. The E39 M5's front and rear sway bars work together to balance understeer and oversteer tendencies.

Benefits of Upgrading Sway Bars on the E39 M5

  • Reduced body roll: A thicker or stiffer sway bar cuts roll angle by 30–50 percent, making the car feel more planted during aggressive cornering.
  • Improved steering response: With less weight transfer, the front tires maintain more consistent grip, sharpening turn-in.
  • Adjustable balance: Many aftermarket sway bars offer multiple end-link mounting holes, allowing you to fine-tune understeer or oversteer characteristics.
  • Retained ride comfort: Sway bars mainly affect roll stiffness, not vertical compliance, so daily driving comfort remains largely unchanged.

Choosing the Right Sway Bars

Material and Construction

Aftermarket sway bars for the E39 M5 are typically made from high-strength spring steel or chromoly. Solid bars are stiffer than hollow bars of the same diameter but weigh more. Hollow bars offer a good stiffness-to-weight ratio. Look for bars with powder-coated or e-coat finishes to resist corrosion. Diameters typically range from 27 mm to 30 mm front and 22 mm to 25 mm rear for the M5.

Adjustability

Adjustable sway bars feature multiple holes in the lever arm where the end link attaches. Moving the end link closer to the bar's center increases effective stiffness; moving it outward softens the bar. This adjustability allows you to dial in understeer or oversteer balance without changing springs. For the E39 M5, a three-position adjustable rear bar is particularly useful for track tuning.

Brand Recommendations

Well-regarded brands for E39 M5 sway bars include Eibach, H&R, Dinan, and Turner Motorsport. Eibach offers their popular anti-roll kit with matched front and rear bars. H&R’s bars are known for durable construction and include polyurethane bushings. Turner Motorsport provides a direct-fit option with adjustable rear bars. Turner Motorsport is a trusted source for BMW performance parts and offers detailed fitment guidance.

Installation Considerations

Installing sway bars on the E39 M5 is a moderately difficult DIY job, but it requires careful attention. The front bar is accessed from under the car after removing the underbody panel. The rear bar sits above the differential and requires dropping the exhaust heat shield. Always replace sway bar bushings with polyurethane units, which resist compression and last longer than rubber. Use anti-seize on the bar ends where bushings ride to prevent squeaks. RealOEM provides exploded diagrams and part numbers to verify compatibility with your specific production date.

Strut Braces – Eliminating Chassis Flex

Strut braces connect the tops of the strut towers, tying the chassis together to resist flex during cornering. The E39 M5’s strut towers are not rigidly connected from the factory, and under hard loads, the front towers can deflect inward, causing bump steer and delayed steering response. A strut brace stiffens this connection, improving steering precision and allowing the suspension to work as intended.

Front Strut Braces vs. Rear Strut Braces

Front strut braces are the most common upgrade for the E39 M5. They span the engine bay, connecting the two front strut towers. Installation is straightforward and does not interfere with the engine. Rear strut braces mount in the trunk, connecting the rear strut towers. They reduce chassis flex from the rear axle, improving stability during corner exit and over uneven surfaces. For most drivers, a front brace provides the most noticeable improvement. Adding a rear brace offers diminishing but real gains, especially on cars with high-mileage chassis.

How a Strut Brace Improves Handling

By mechanically linking the strut towers, a brace prevents them from moving independently. This keeps the suspension geometry more consistent as the car loads up. Steering becomes more direct, with less delay between input and tire response. The effect is most noticeable during rapid transitions, such as slaloms or chicanes, where chassis flex would otherwise introduce vagueness. A good strut brace also reduces stress on the strut tower mounting points, potentially preventing cracks in high-mileage cars.

Choosing the Right Strut Brace for Your E39 M5

Material and Design

Strut braces are made from steel, aluminum, or carbon fiber. Steel offers the highest stiffness but adds weight. Aluminum is lighter and provides excellent rigidity for street and track use. Carbon fiber braces are lightweight but often more expensive and less stiff than metal alternatives. The brace should have solid mounting plates that distribute load evenly across the strut tower. A three-point brace that also connects to the firewall offers additional stiffness.

Brand Recommendations

Mason Engineering produces some of the most respected strut braces for the E39 M5, using chromoly steel and precision CNC-machined mounts. Strong-Strut offers a unique "triangulated" design that connects to the firewall for increased rigidity. Dinan and Turner Motorsport also offer well-engineered braces that are direct-fit for the E39. For a comprehensive selection, Mason Engineering has specialized in BMW chassis bracing for years.

Installation Notes

Installing a strut brace is typically a one-hour job. Remove the strut tower caps, clean the mounting surfaces, and torque the brace's bolts to factory specification (usually around 16–18 ft-lbs for the E39). Ensure the brace clears the engine cover, intake, and brake reservoir. Some braces require slight spacing to avoid contact. Periodically check torque after installation, as chassis flex can loosen the bolts over time.

Alignment – The Final Piece of the Puzzle

After installing upgraded sway bars and strut braces, alignment becomes critical. A proper alignment ensures that all the new suspension components work together harmoniously. The E39 M5’s factory alignment specs were conservative, and a more aggressive alignment can unlock significant grip without adding negative handling traits.

Key Alignment Angles Explained

Camber

Camber is the inward or outward tilt of the wheel relative to vertical. Negative camber improves cornering grip by keeping the tire's contact patch flat during body roll. On the E39 M5, front camber is usually around -0.5 to -1.0 degrees from the factory. For street performance, -1.5 to -2.0 degrees front is a common target. More than -2.5 degrees may cause uneven street tire wear. Rear camber is less adjustable without aftermarket arms, but -1.5 to -2.0 degrees is typical for upgraded cars.

Toe

Toe refers to whether the front of the tires point inward (toe-in) or outward (toe-out). Toe-in provides straight-line stability, while toe-out improves turn-in response. For a street-driven E39 M5, a slight front toe-in of 0.05 to 0.10 degrees per side is recommended. For track use, a very slight toe-out (0.05 degrees) can sharpen initial turn-in. Rear toe should always be slightly toe-in (0.10–0.15 degrees total) to maintain stability under power.

Caster

Caster is the angle of the steering axis, which affects steering feel and straight-line stability. Higher caster increases steering effort and self-centering. The E39 M5 has limited caster adjustment from the factory, but aftermarket adjustable control arms can increase caster to improve high-speed stability. Caster is not typically a primary adjustment for most drivers.

Here are baseline alignment targets for a street-focused E39 M5 with upgraded sway bars and strut braces:

  • Front camber: -1.5 to -2.0 degrees
  • Front caster: As close to 6.5 degrees as possible (factory spec)
  • Front toe: 0.05 to 0.10 degrees toe-in per side
  • Rear camber: -1.5 to -2.0 degrees
  • Rear toe: 0.10 to 0.15 degrees toe-in total

For a dual-purpose street and track car, consider -2.0 to -2.5 degrees front camber and 0.0 to 0.05 degrees front toe-out. Rear camber can stay at -2.0 degrees. Always document your settings so you can return to a known baseline.

Choosing a Professional Alignment Shop

Not all alignment shops are equipped to handle a performance-oriented E39 M5. Look for a shop that specializes in BMW or performance vehicles and uses a modern rack with Hunter or similar alignment equipment. Discuss your driving style and upgrade goals with the technician. Ask if they can perform a "corner balance" if you have coilovers. A custom alignment typically costs $100–$200 and is worth every penny. Online BMW forums like Bimmerpost are good resources for finding alignment specialists in your area.

Putting It All Together – A Complete Handling Package

Sway bars, strut braces, and alignment do not exist in isolation. Combined, they form a cohesive handling package that transforms the E39 M5.

Synergistic Benefits

Stiffer sway bars reduce body roll, allowing the strut brace to work more effectively by limiting the forces that flex the chassis. A stiffer chassis then delivers more precise steering inputs to the tires, which are held at optimal camber angles thanks to a proper alignment. The result is a car that responds instantly, holds a line through corners with minimal steering correction, and inspires confidence at higher speeds. Tire wear becomes more even, and brake performance improves because the chassis is more stable under load.

  1. Start with alignment: Even before swapping parts, get a baseline alignment to document current settings and identify worn components.
  2. Install strut braces: Front brace first, then rear if desired. This stiffens the platform for subsequent upgrades.
  3. Upgrade sway bars: Choose adjustable bars to allow future tuning. Install polyurethane bushings for longevity.
  4. Final alignment: After all hardware is installed, return to your alignment shop. Set camber and toe to your performance targets.

This sequence minimizes rework and ensures each component contributes optimally to the final setup.

Frequently Asked Questions

Will upgrading sway bars make my E39 M5 ride harsh?
No. Sway bars primarily affect roll stiffness, not vertical compliance. Ride quality over bumps and potholes remains similar to stock. However, hitting a single-side bump, like a speed bump at an angle, may feel firmer because the sway bar transmits load to the opposite wheel.

Do I need to upgrade my springs and dampers at the same time?
Not necessarily. Sway bars and strut braces work with factory or aftermarket springs and dampers. If your current shocks are worn or if you want a lower ride height, upgrading springs and dampers is complementary but not required for these modifications to be effective.

Can I adjust strut braces after installation?
No, strut braces are fixed once installed and torqued. They do not offer adjustability like sway bars. Choose a brace that fits your intended use – a triangulated front brace for maximum stiffness is usually the best choice for most drivers.

How often should I align my E39 M5?
At least once a year or after any suspension component change. If you notice uneven tire wear or the car pulling, check alignment immediately. Track-driven cars may need alignment adjustments every few events.

Conclusion

Upgrading the sway bars, installing strut braces, and performing a precision alignment are three of the most effective handling and safety upgrades available for the BMW E39 M5. These modifications work together to reduce body roll, sharpen steering response, and eliminate chassis flex, resulting in a car that is more capable and confidence-inspiring on any road or track. By following the upgrade path recommended here and consulting trusted sources like Turner Motorsport, Mason Engineering, and Bimmerpost, you can extract the full potential from one of BMW’s greatest creations. The investment in time and parts is modest compared to the transformation in driving experience, and the improved safety makes every journey more secure.