How a simple torsion spring shaped Porsche's rear-engine handling
From the earliest through-body 911 bars to today's fully adjustable Tarett systems.
Few parts on a classic Porsche 911 are as simple in appearance, yet as influential in feel, as the sway bar. It is just a torsion spring connecting the left and right sides of the suspension, but on a rear-engine Porsche it can change the whole personality of the car. From the early through-body bars on the first 911s and 912s to the underbody bars on the final G-body SC's and modern cars, Porsche's sway-bar history tells a great story about handling, production engineering, and the constant balancing act between comfort and performance.
What a Sway Bar Actually Does
A sway bar, also called an anti-roll bar or stabilizer bar, connects the suspension on one side of the car to the suspension on the other side. When both wheels move together, as they do over a speed bump, the bar does very little. But when the car corners and the outside suspension compresses while the inside suspension extends, the bar twists. That twist resists body roll. More front roll stiffness generally adds understeer. More rear roll stiffness generally helps the car rotate, sometimes to the point of oversteer.
The effective stiffness of a sway bar is not determined by diameter alone. Bar diameter matters, but so do material, arm length, bushing compliance, drop-link angle, and where the link attaches to the arm. Adjustable sway bars use the arm length to change the bar's effect. Move the drop link farther out on the arm and the suspension has a longer lever to twist the bar, making the bar act softer. Move the link inward and the lever arm gets shorter, making the bar act stiffer.
Adjustable drop links are just as important. During a proper corner balance, the sway bars can be disconnected, the car can be balanced on the scales, and then the drop links can be adjusted so the bars reconnect without preload. If the links are too long, too short or not adjustable at all, the bar can quietly load one side of the car while it sits at rest. On a 911, where balance and predictability are everything, a neutral, properly adjusted sway bar can be the difference between a car that feels sharp and one that feels slightly confused.
Before the 911: A Quick Look at the 356
Porsche was thinking about roll control before the 911 arrived. The earliest 356 models did not use a front sway bar. As the 356 evolved, Porsche added a front bar to improve stability and make the rear-engine chassis more forgiving at speed. The 356A and 356B used a 15 mm front sway bar, while the later 356C increased that to 16 mm.
Rear sway bars were not a typical factory feature on 356 road cars in the same way they later became part of the 911 conversation. Porsche's approach on the 356 was mainly to use a front bar to calm the chassis and reduce the oversteer tendencies that could come with rear-engine weight distribution, swing-axle geometry, and narrow period tires.
That background matters because the 911 inherited the same basic challenge: keep the agility and traction of a rear-engine Porsche, but add enough roll control and stability to make the car fast, predictable, and usable by real drivers.
When the 911 and 912 arrived, Porsche continued developing its roll-control strategy in a distinctly 911 way. The earliest 911 and 912 front sway bars were through-body designs. The bar passed through the front body structure, with arms and drop links connecting it to the front suspension.
The Early 911 and 912: Through-Body Front BarsAmong the earliest base 911 and 912 applications, the familiar front bar was the 13 mm through-body stabilizer. The 911S received a larger 15 mm front bar, and factory parts references also show other early front-bar sizes, including 11 mm (one year only 911L Hydropneumatic car), 14 mm, and 16 mm variations depending on model, year, market, and application. The 13 mm bar is important because it represents the starting point for the 911's production sway-bar story. It was not a giant performance part. It was a relatively small sway bar intended to add roll control while preserving ride quality and front-end compliance. The early cars were light, narrow, and riding on period tires. Porsche did not need enormous bar rates to make the car respond. The through-body design itself is elegant. The bar is mounted high and passes through the chassis, with external arms operating the drop links. From an aftermarket performance perspective, this gives clean geometry and makes the system friendly to adjustment. That is one reason the through-body concept never disappeared from the performance world. Many through-body and modern adjustable sway-bar systems for early 911s still use the same basic idea. |
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Rear Sway Bars on the Early CarsThe rear sway-bar story is more nuanced. The rear bar was not a through-body design. It was mounted at the rear suspension and trailing-arm area. Early rear bars were associated especially with 911S models and sport-equipped cars rather than being universal on every base 911 or 912. In the 1967–1968 period, Porsche used or cataloged 16 mm rear stabilizers in early 911S and retrofit-style applications. By 1969 and 1970, 15 mm rear bars appeared on S and sport/M-option applications. On these early cars, the presence of a rear bar can depend on model, options, market, and later modifications. After six decades, many cars have also had tabs added, removed, repaired, or changed. |
Through vs. Underbody Bars: Finding a CompromiseFor 1970 through 1973, the longhood 911 continued with the through-body front bar. The common sport-oriented factory combination was 15 mm front and 15 mm rear on 911S, Carrera RS-type applications, and 911T or 911E cars equipped with the appropriate M or sport suspension equipment. A comfort-oriented T or E was not necessarily equipped the same way as an S. That distinction matters for restorers trying to determine what is correct for a particular chassis. The through-body front bar has several advantages. The geometry is excellent, the system lends itself well to adjustability, and the layout is very motorsport-friendly. That is why through-body style bars and many modern adjustable systems still follow that concept. There are downsides. A through-body bar requires openings in the body shell, along with seals, bushings, plates, and reinforcement. That means more assembly time and more opportunity for water, dirt, corrosion, or poor installation to become a problem. On cars not originally built for a through-body bar, proper reinforcement is essential. The underbody bar has a different set of virtues. It is simpler, easier to package, easier to install on a production line, and easier to standardize across multiple models. It also avoids passing the bar through the body shell. |
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The tradeoff is that it is not flexible from a performance-tuning perspective. Factory underbody bars are not adjustable, and serious performance builders usually convert later cars back to an early through-body style arrangement when they want maximum tuning flexibility.
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1974: A Time of Pivotal ChangeThe 1974 model year was a major turning point for the 911. The newly-introduced US impact-bumper regulations brought revised body structure, new bumper hardware, and a more production-oriented evolution of the platform. This is when the regular 911 moved away from the through-body front sway bar and adopted the underbody front sway bar. Why did Porsche change? There does not appear to be one simple factory quote saying, "we changed because of this." But the engineering logic is clear. The underbody bar was easier to manufacture, assemble, seal, and standardize across the growing G-body range. A through-body bar requires accurately located holes through the body, plus sealing hardware, guide parts, bushings, arms, and reinforcement. Every body opening is another place Porsche had to manage alignment, noise, water, corrosion, and production variation. |
Assembly mattered. If you understand the assembly process it makes more sense. You can easily discern that "somebody" had to be on the line, ahead of the front suspension installation. That position was also an "option" position. E.G. if someone ordered a 1971 911T with a sway-bar package, it had to be noted on the build sheet and added prior to the front end being installed. The underbody bar simplified that. It was not necessarily a better racing solution, but it was a very good road-car solution.
The "Ghost" LocationsOne interesting detail is that all of the later body shells still have the stamped or impressed areas in the sheet metal where a through-body bar would have passed through. Anyone who has converted an underbody car to a through-body style front bar would have used these "ghost" locations in the inner fender area. They are a reminder that the 911 body shell evolved rather than starting from zero. But stamped areas are not the same thing as factory through-body fitment. On normal 1974-on 911 models, the production sway bar was the underbody style unless the car falls into one of the early Turbo exceptions or has been modified later. |
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G-Body Sway-Bar Progression
The 1974–1977 regular G-body 911, 911S, and Carrera models commonly used a 16 mm underbody front bar, with larger 20 mm front bars appearing in factory catalog applications and performance variants. Rear bars were now more broadly part of the package, with 16 mm rear bars used on 911, 911S, and Carrera applications.
By the time the 911SC hit the market, Porsche settled into the well-known 20 mm front and 18 mm rear combination. This setup was used through the 1978–1983 SC period and carried into the early 3.2 Carrera years. It is a good example of Porsche's road-car compromise: enough bar to give the car a more modern, tied-down feel, but not so much that it becomes nervous or harsh.
For the 1984 and 1985 Carrera 3.2, the factory combination remained 20 mm front and 18 mm rear. In 1986, as the cars themselves became heavier, Porsche increased the Carrera bars to 22 mm front and 21 mm rear. That setup continued through the final 1989 Carrera 3.2. Those late Carreras have a more controlled feel than the earlier cars, and the sway-bar package is one piece of that character.
The bars did not act alone. The late G-body cars also benefited from years of refinement in tires, alignment settings, shock tuning, torsion-bar selection, and Porsche's own understanding of what customers expected from a 911. The sway bars were part of a complete chassis package, not a standalone cure-all.
The 930 Turbo Outlier
The early 930 Turbo is the wonderful exception that keeps this story from being too tidy. The standard 1974-on 911 moved to the underbody front sway bar, but the early 3.0-liter Turbo retained the through-body-style front bar.
This was not accidental. The first 930s were low-volume, high-performance cars tied closely to Porsche's Carrera RS, 3.0 RS, RSR, and turbocharged racing development. They were not simply normal 911s with more power. They had wider tires, wider bodywork, far more torque, and a much more demanding handling envelope.
The Reinforced Lever Arm FixThe early Turbo used a 19 mm through-body-style front bar and an 18 mm rear bar. That front layout gave Porsche known geometry and a proven performance solution on a car that needed very careful balance. With the 930's rear weight bias and sudden boost delivery, Porsche needed roll control without creating a car that was too eager to rotate at the wrong moment. This increase in bar size and performance led to another unique 930 part: the reinforced lever arm. Porsche found that the sheetmetal for the stock lever arms was deforming, thereby reducing the effectiveness of the sway bar setup, so they added angle iron reinforcements at the interface of the lever arm and sway bar. This fixed the problem and kept the 930 Turbo's handling razor sharp. |
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The Turbo Goes UnderbodyAs the Turbo matured into the later 3.3-liter production platform, Porsche moved it into the standardized underbody G-body architecture. The 1978–1984 930 used a 20 mm front and 18 mm rear setup. The 1985–1988 Turbo stepped up to 22 mm front and 20 mm rear. The 1989 Turbo remained 22 mm in front but used an 18 mm rear bar, one of those one-year details that keeps Porsche parts people humble. This shift applied across the G-body lineup: fewer body openings, simpler sealing, and a chassis architecture shared with cars that no longer needed through-body tooling. Even so, the Turbo's underbody bars stayed larger than the standard 911's, a sign that Porsche was willing to trade the through-body's tuning purity for manufacturing sense without giving up the wide-body car's planted, tail-happy character. |
Tarett Engineering and the Modern Tuning ApproachThat brings us to the modern aftermarket, and specifically to Tarett Engineering. Tarett Engineering was established in 1995 and built its reputation around competition suspension components for the Porsche racing community. The company's approach is practical and engineering-driven: make parts that solve real handling problems, use strong materials, include adjustment where adjustment matters, and build components that can survive serious use. Tarett's sway-bar systems are a great example of that philosophy. For classic 911, 912, 930, and 914 applications, Tarett offers front sway-bar and drop-link kits that convert or update the car with through-body configurations. They even offer hollow bars that are designed to provide the stiffness of a comparable solid bar with less weight. Many systems use 4130 chrome-moly steel, proper bearing blocks, adjustable arms, and high-quality drop links. The point is not just to make the bar bigger. The point is to give the installer and driver a precise tuning tool. |
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For the classic 911 and 912, Tarett offers front and rear sway-bar and drop-link solutions, including RSR-style systems for cars being built toward an RS, RSR, ST, vintage race, or high-performance street application. These kits keep the period-correct spirit of the original racing parts but add modern materials, improved adjustability, and more robust hardware. For 1974–1989 911s that originally used underbody front bars, these kits typically require conversion to through-chassis mounting with the correct adapters and reinforcement hardware (some welding required).
Tarett also supports the 914 community, which makes sense given how much the 914 benefits from careful chassis tuning. Their 914 front sway-bar and drop-link products are aimed at improved balance, adjustable roll stiffness, and more precise handling for street, track, and vintage racing use. Like the 911, a 914 responds dramatically to thoughtful suspension setup.
Beyond sway bars, Tarett's broader Porsche product line includes components such as drop links, control arms, bushings, toe links, camber plates, and related suspension hardware for multiple Porsche platforms. The common thread is adjustability with purpose. A rod end or turnbuckle is not there to look exotic. It is there so the alignment, corner balance, bump steer, or sway-bar preload can be set correctly.
That philosophy fits classic Porsches perfectly. A 911 does not respond well to random stiffness. You cannot simply install the largest front and rear sway bars and assume the car will be faster. The suspension has to be treated as a system. Torsion bars, shocks, tire choice, ride height, alignment, bump steer, bushings, corner balance, and sway bars all interact.
Choosing the Right Setup
For some 1965–1989 911s, the right answer might be a stock-style restoration. A narrow, early 911 on period-correct tires may feel best with the correct small through-body front bar and the appropriate rear bar, if the car was equipped with one. For a concours or preservation-minded car, correctness matters.
For other cars, especially those on modern tires or used in spirited driving, autocross, DE, or vintage racing, an adjustable sway-bar system can transform the car. The key is choosing the correct rate range, installing the bar correctly, reinforcing the chassis where needed, and setting the drop links neutrally after the corner balance is complete.
Stock vs. aftermarket: As above, for concours or preservation-minded builds, stock might be the way to go. That said, with complete stock setups selling for over $600.00 on the used market, a fully adjustable, precision-engineered Tarett bar is an immense improvement for roughly the same price. Add a restoration with new bushings to that $600.00 used bar and you're well over the price of a new, fully adjustable bar. Modern bars with longer, adjustable arms can emulate stock 15 mm bars or larger 21 mm bars. Aftermarket is starting to make sense with anything other than a concours build.
The mistake is thinking of sway bars as isolated parts. They are not. A large front bar on soft torsion bars may make the car feel flat, but it can also reduce front grip and increase understeer. It can also be one of the largest contributors to a "harsh" ride. A large rear bar can make a 911 rotate beautifully, or it can make the car nervous if the rest of the setup does not support it. The correct sway-bar setup should make the car more predictable, not just flatter.
Conclusion
The history of Porsche sway bars is really the history of Porsche chasing balance. The 13 mm through-body front bar on the earliest 911 and 912 models, the 16 mm sport bars of the longhood era, the broader use of rear bars on S-option cars, the 1974 move to underbody bars, the 20/18 SC and Carrera combinations, the 22/21 late Carrera setup, and the early Turbo's through-body exception all reflect Porsche adjusting the same basic equation: stability, response, grip, comfort, and control.
At PMB Performance, that is exactly the kind of detail we love helping owners sort through. Whether your goal is factory-correct restoration, a sharper canyon car, a vintage race build, or simply replacing tired links and bushings with the right components, the sway bar should be considered part of the whole suspension system. The right parts, installed correctly and adjusted thoughtfully, can make a classic Porsche feel the way Porsche intended—or the way you always wished it did.