Audi B9 & B9.5 S4 & S5

The B9 and B9.5 Audi S4 and S5 represent the evolution of Audi’s midsize performance lineup, positioned as direct rivals to the BMW M3 and M4. Introduced in 2017 alongside the A4 and A5, and expanded with S-line variants in 2018, these models are available in sedan, coupe, wagon, and Sportback body styles. Built on the MLB Evo B platform—a progression of the previous MLB B used in the B8 generation—they bring significant improvements in chassis dynamics, design, and mechanical engineering. While some components are shared with the outgoing B8, the B9 lineup is largely all-new. MLB stands for “Modular Longitudinal Matrix” (Modularer Längsbaukasten in German), highlighting Audi’s modular approach to longitudinal engine architecture. Key changes from the B8 include the switch from a supercharged 3.0T V6 to a more efficient turbocharged 3.0T in the S4 and S5, and the replacement of the DL501 dual-clutch transmission with the smoother, more robust ZF 8-speed automatic, branded as Tiptronic. Manual transmissions were entirely dropped from the S4/S5/RS5 lineup in this generation.

Across the board, the B9 models outperform their B8 predecessors in terms of interior refinement, technology, aesthetics, and mechanical reliability. The introduction of the A5 Sportback—a sleek four-door hatchback—shifted market demand, making the A5 and S5 more popular than the traditional A4 and S4. Despite the different body styles, these models are mechanically identical, and the choice comes down to personal preference in styling and practicality. The S5 is available in coupe, convertible, and Sportback configurations, offering flexibility to a wide range of buyers. The B9 received a minor update in 2019 with new bumpers inspired by the S4, followed by a more comprehensive facelift in 2020 that refreshed the interior tech and exterior styling. Enthusiasts commonly refer to the 2017–2019 models as “B9” and the 2020+ versions as “B9.5,” though Audi itself does not officially use this designation.

 

Engine 3.0t (EA839)	Engine Oil Type VW 508 00/509 00 | 0W-20 Engine Oil Capacity 7.5 Liters Audi Engine Oil Change Kit - Liqui Moly 06M198405FKT SKU: KIT-06M198405FKT View Product QTY $134.23+
Transmission ZF 8HP (8HP55A)	Transmission Fluid Type ZF Lifeguard 8 Transmission Fluid Capacity 9 Liters Full Replacement | 4.5-5.5 Liters Drain & Fill Audi ZF8 Automatic Transmission Service Kit - Liqui Moly LM20032KT SKU: KIT-LM20032KT View Product QTY $102.75+
Differential Rear Diff (Standard)	Differential Fluid Type Audi G 052 145 S2 | 75W-85 GL-5 Differential Fluid Capacity 1 Liter Audi Differential Gear Oil - Genuine Audi G060190A2 SKU: VAG-G060190A2 View Product QTY $53.99+
Differential Rear Diff (Sport)	Differential Fluid Type Audi G 055 515 A2 Differential Fluid Capacity 1.1-1.3 Liters Audi Differential Fluid Service Kit - Genuine Audi G055190A2KT SKU: KIT-G055190A2KT View Product $102.14x
Brake	Brake Fluid Type DOT 4 Low Viscosity | VW 501 14 Brake Fluid Capacity 1.0-1.5 Liters DOT 4 SL.6 Brake Fluid (1 Liter) - ATE 706402 SKU: ATE-706402 View Product QTY $16.14+

Audi B9 S4/S5 ZF-8 Speed Transmission Guide

ZF 8-Speed (8HP55) Transmission Service

The Audi B9 S4 and S5, equipped with the 3.0L EA839 turbo V6 and ZF 8-speed automatic transmission (8HP55), are generally regarded as robust platforms, but a few drivetrain-related issues have emerged as mileage and tuning become more common. One of the more reported concerns is ZF transmission hesitation or harsh shifting, particularly during low-speed driving or after software tunes, though this is often resolved or improved with a TCU (transmission control unit) tune and or servicing.

Transmission Mount Inserts

The DSG and ZF 8HP are two quick-shifting transmissions backed up by engines with plenty of torque. Aggressive shifts and spirited driving will strain the transmission mounts, which are made of relatively soft rubber. Leaving them as is can cause them to wear quickly. Instead, you can install 034Motorsport transmission mount inserts and have a firmer bushing that lasts much longer.

Worn mounts introduce sloppy shifting and a jerky motion when setting off from a stop. You can replace the original mount, but it will wear just as quickly. Installing the billet aluminum inserts into the gaps in the bushing will reduce how much it is allowed to flex, preventing it from wearing as quickly. It will provide a firmer mount, but there's a minimal increase in NVH.

Front Differential & Transfer Case Service

Audi refers to the fluids in your vehicle’s transfer case and front differential as “lifetime,” but in the real world, no fluid lasts forever. These components operate under high stress, and over time, their fluid breaks down, losing the ability to properly lubricate and protect critical parts.

What Audi means by “lifetime” isn’t the same as forever. In fact, ZF (the manufacturer of many Audi driveline components) and other OEM suppliers recommend fluid service intervals to keep things running smoothly for the long haul.

Neglecting these fluids can lead to wear, drivability issues, and costly repairs. Regular fluid changes are a small investment that pays off in performance, reliability, and peace of mind. And that’s exactly why our team at FCP Euro went ahead and made service kits for your front differential, transfer case, rear differential, and more. We recommend performing these services every 40,000 to 50,000 miles.

Rear Differential Service

Quattro AWD system components, such as the rear differential or sport rear diff (if equipped), can develop noise or fluid seepage over time, particularly if the differential fluid isn’t changed regularly—something Audi doesn’t list as part of standard service but is recommended by many independent shops every 35k–50k miles. While catastrophic failures are rare, preventative maintenance and tuning-aware upgrades (like upgraded mounts or driveshaft inserts) can go a long way in preserving drivetrain health in these performance-oriented models.

The Audi B9 S4 and S5 generally offer solid suspension and chassis durability, but as these vehicles age, especially with spirited driving or lowered setups, certain wear items begin to show their limits. Common issues include premature wear in control arm bushings and ball joints, particularly in the front multi-link suspension, leading to clunking noises, vague steering, or uneven tire wear. Sway bar end links can also develop play over time, especially if the car has been lowered or driven aggressively. For models equipped with the adaptive damping suspension, failures in the electronic dampers can occur, usually showing up as ride harshness, fault codes, or leaking struts—replacement costs for these are notably higher than standard dampers. Additionally, front strut mounts and bearings may begin to creak or bind as mileage climbs. Regular inspection, especially around the 50,000–70,000-mile mark, along with proactive bushing or damper replacement, helps maintain tight chassis feel and driving precision. For lowered cars, keeping alignment in spec is critical to avoid accelerated tire and suspension component wear.

Control Arm Bushings & Ball Joints

The Audi B9 S4 and S5 use a sophisticated five-link front suspension that relies on multiple aluminum control arms with integrated rubber bushings and ball joints to manage ride quality and steering precision. Over time, especially with aggressive driving, lowered suspension setups, or high mileage, these bushings can degrade, and the ball joints may develop play or clunking, leading to vague steering feel, front-end noise over bumps, and uneven tire wear. Although the arms themselves are typically structurally sound, the bushings are not serviceable separately in most OEM configurations, requiring full arm replacement when wear sets in. Common signs of failure include knocking during braking, steering wander, or a loose, floaty front-end feel. Aftermarket options from brands like Lemförder, Meyle HD, and 034Motorsport offer enhanced durability or performance-focused alternatives, some with stiffer bushings or fully spherical joints for track use.

Subframe Mounts

Some owners have experienced driveline clunks or vibrations, which can stem from worn center support bearings, engine mounts, transmission/subframe mounts, or axle alignment issues. Even though these cars are fairly new, depending on the mileage and how and where the car has been regularly driven, it could be time to replace your subframe mounts.

Battery Replacement

Modern automotive battery replacements are no longer simple. What was once a ten-minute job has become one requiring a specialized scan tool. Luckily, Rusty Herten, FCP Euro's In-House Technician, is here to show you how it's done for an Audi B9 model, such as this S5 Sportback. Engine batteries are the source of electricity for the entire car. They have a lifespan of about five years, so anything beyond that is a risk. A faulty or failing battery doesn't provide enough electricity, causing dim lights, misfires, long cranks, trouble starting, and other funky electrical issues. Every B9 model has a battery located in the trunk. After installing the new battery, you'll have to hop inside the car and plug in an advanced scan tool. With it, you need to enter a specific code from the side of the battery into the engine computer so it knows the battery's proper settings.

Cabin Air Filter Replacement

The cabin air filter helps keep your interior clean and smelling nice. In doing so, it picks up and blocks all sorts of contaminants that the HVAC system pulls in to provide heat or A/C. Replacing the filter at its scheduled interval is the best way to ensure your Audi always has quality air coming through the vents. Failing to replace it on time can lead to some stinky results. Blocking dirt, dust, and debris is a tough job that can only be done for so long. A typical cabin air filter replacement interval is around 30,000 miles, depending on the driving environment. Polluted or dusty areas can force an earlier replacement. You may notice a musty or moldy smell and reduced air flow with an old or partially blocked filter.

Aftermarket Exhaust

Upgrading the exhaust system on the B9 Audi S5 is one of the most effective ways to enhance both performance and driving engagement. The factory exhaust is designed with comfort and sound insulation in mind, which leaves the EA839 3.0T V6 sounding more muted than many enthusiasts would prefer. Aftermarket exhaust systems not only unlock a deeper, more aggressive tone but also reduce backpressure and improve exhaust flow, contributing to better throttle response and potential horsepower gains when combined with other supporting mods. Full cat-back systems from brands like AWE and APR offer various sound profiles ranging from refined to race-inspired, often with valved configurations to retain OEM drive mode functionality.

For those looking for a more budget-friendly yet impactful option, the 034Motorsport Resonator Delete Kit is a popular entry point. This simple bolt-in upgrade removes the factory mid-pipe resonator, replacing it with a straight-through section that enhances volume and clarity without introducing excessive drone. It maintains emissions compliance and stock mufflers, making it a great choice for daily drivers who want more character from their exhaust without a full system swap. Whether you’re chasing peak performance or simply want your S5 to sound like it should have from the factory, the aftermarket exhaust scene offers a range of solutions to suit every goal and budget.

Transmission Tunnel Brace

The B9-chassis Audi models feature a brace along the drive shaft tunnel under the car. Some owners have found that aftermarket exhausts can hit the bracket, causing unwanted driving noises. Luckily, aftermarket performance supplier 034Motorsport makes a billet brace to replace the original. It adds 8mm of clearance in the tunnel, allowing larger-diameter aftermarket systems to fit without any clearance issues.

Two-Piece Slotted Rotor Upgrade

The B9 and B9.5 Audi S4 and S5 come equipped with 350mm front rotors, which provide solid braking performance for daily driving and spirited use. However, enthusiasts looking to improve stopping power, fade resistance, and pedal feel often turn to popular upgrades. These include lightweight 2-piece rotors to reduce unsprung mass, performance brake pads, stainless steel braided lines for better pedal feedback, and high-temperature brake fluid. For those seeking more aggressive performance or track use, aftermarket big brake kits from brands like 034Motorsport offer larger calipers and rotors specifically designed for the B9 chassis. In the rear, the single-piston sliding calipers with integrated electronic parking brake can also benefit from upgraded pads and rotors, though full rear upgrades are more limited due to the e-brake integration.

Brake Pad Upgrade

The brake pads that ship with your B9 Audi aren't made to be the highest-performance pads out there; they're made to balance performance, how much brake dust they create, and noise levels. The average driver doesn't want to be washing their wheels weekly or to be subjected to the high-pitched squeal of brakes when at the drive-through for their morning coffee. While they do work for most, if you want more out of your B9 for those spirited drives on some back roads, or the occasional autocross or track day, we have a catalog of options for you.

With pad upgrades from companies such as APR, 034Motorsport, and EBC, you can find a brake pad as aggressive as you could ever want.

Track-Ready Brake Fluid

If you’re a regular track-day goer, you’ll also want to upgrade to a higher-caliber brake fluid. You can read all about the nuances of brake fluid types and what they’re meant for over on our blog, but in short, know that the OE brake fluid won’t survive much longer than the OE brake pads. The Audi B9 S4 and S5 are relatively heavy and make lots of power, so the brakes often generate lots of heat, which is then transferred into the brake fluid. Fluid meant to withstand the race track has a much higher boiling point than one meant for daily driving, and skipping on it may mean losing your brakes at the end of the fastest part of the track you're on. Flushing out the OE fluid for something more durable is one of the least expensive and most meaningful changes you can make for your Audi's performance and your safety.

Strut Brace Upgrade

Cars like the Audi S5 and S4 are meant for performance driving. Chassis stiffness plays a large role in how engaging a car can be, and many owners work toward making their car stiffer. While the B9 chassis is very rigid on its own, aftermarkets like 034Motorsport have come out with effective and good-looking upgrades any Audi B9 owner can take advantage of. The billet aluminum strut tower brace connects the strut tops to the firewall. Triangulating those points stiffens the front suspension, allowing the dampers, springs, and bushings to all work more effectively. It also adds a bit of understated bling to the engine bay, which is never bad.

Coilover Suspension

The Audi B9 S4 and S5 come equipped with a five-link independent suspension at all four corners, providing a solid balance between comfort and handling. From the factory, these cars offer either a standard fixed suspension or an optional adaptive damping system (Audi Drive Select), which adjusts shock absorber firmness based on driving mode and road conditions. In Comfort mode, the ride is smooth and composed for daily driving, while Dynamic mode tightens things up for better body control and more responsive handling. While the stock setup is well-tuned for a premium sport sedan or coupe, it still leaves room for improvement in terms of ride height, cornering sharpness, and road feedback, especially for enthusiasts looking for a more aggressive driving experience or visual stance.

Upgrading the suspension on the Audi B9 S4 and S5 is a popular way to enhance both aesthetics and handling performance. Lowering springs are the most budget-friendly option and are ideal for those who want a subtle drop in ride height (typically 0.75"–1.5") to eliminate wheel gap and improve stance. Paired with the factory dampers—especially the optional adaptive suspension—they provide a firmer, sportier ride without drastically affecting daily comfort. For enthusiasts seeking greater adjustability and sharper handling, coilovers are the next step. Coilover kits allow fine-tuning of ride height, damping (in some cases), and in certain setups, even camber and rebound. While coilovers are more of an investment, they offer superior performance, control, and customization, making them ideal for drivers who prioritize precision or plan to track their cars. Both options transform the driving experience by reducing body roll, improving cornering feel, and enhancing road presence.

The Audi B9 S4 and S5, introduced for the 2018 model year, represent the performance-oriented versions of the A4 and A5, respectively. Built on Audi’s MLB Evo platform, the B9 generation brought a lighter and more rigid chassis compared to its predecessor, improving both handling and efficiency. The S4 is offered exclusively as a sedan, while the S5 comes in three body styles: Coupe, Sportback, and Cabriolet. Both models are part of Audi’s “S” lineup, positioned just below the high-performance RS variants.

Powering the B9 S4 and S5 is a 3.0-liter turbocharged V6 engine (EA839) producing 354 horsepower and 369 lb-ft of torque. This engine replaced the supercharged V6 from the previous generation, offering stronger low-end torque and improved fuel efficiency. Paired with an 8-speed ZF automatic transmission and Audi’s Quattro all-wheel-drive system, these cars achieve 0–60 mph in approximately 4.4 seconds. Notably, Audi moved away from the dual-clutch transmission used in earlier models in favor of the smoother and more robust torque-converter automatic.

The B9 S4 and S5 feature adaptive dampers (standard or optional, depending on trim), Audi Drive Select, and an optional sport differential for enhanced handling. Inside, both models are equipped with high-end technology, including Audi’s Virtual Cockpit, the MMI infotainment system, and premium interior materials. Optional upgrades include a Bang & Olufsen sound system, a head-up display, and a variety of driver assistance features. A mid-cycle refresh in 2020, known as the B9.5, brought sharper exterior styling, a revised infotainment interface with a larger touchscreen, and other interior updates. Production continued through the 2023 model year with minor refinements along the way.

Audi B9 S4 & S5 (North America)

Engine: 3.0L Turbocharged V6 (EA839)

Horsepower: 354 hp @ 5,400–6,400 rpm

Torque: 369 lb-ft @ 1,370–4,500 rpm

0–60 mph: ~4.4 seconds (varies slightly by body style and trim)

Transmission: 8-speed ZF automatic

Drivetrain: Quattro all-wheel drive

Audi B9/B9.5 S4 and S5 Wheelbases

S4 Sedan: 111.2 inches (2,825 mm)

S5 Coupe: 108.8 inches (2,764 mm)

S5 Sportback: 111.2 inches (2,825 mm)(Same as the S4, since it shares the A4/S4 chassis platform)

S5 Cabriolet: 108.9 inches (2,766 mm)

Audi B9/B9.5 S4 & S5 Curb Weights

S4 Sedan: 3,890–3,925 lbs (1,765–1,780 kg)

S5 Coupe: 3,850–3,880 lbs (1,746–1,760 kg)

S5 Sportback: 3,900–3,925 lbs (1,769–1,780 kg)

S5 Cabriolet: 4,090–4,115 lbs (1,855–1,867 kg)

Audi B9 S4 Wheel & Tire Sizes

Standard Wheel Size:

Front & Rear: 18 x 8.5 inches

Tires: 245/40 R18

Optional Wheel Size:

Front & Rear: 19 x 8.5 inches

Tires: 255/35 R19

Optional (Sport Package):

Front & Rear: 20 x 8.5 inches

Tires: 255/30 R20

Audi B9 S5 Wheel & Tire Sizes

Standard Wheel Size (Coupe & Sportback):

• Front & Rear: 18 x 8.5 inches
• Tires: 245/40 R18

Optional Wheel Size (Coupe & Sportback):

• Front & Rear: 19 x 8.5 inches

• Tires: 255/35 R19

Optional (Sport Package):

• Front & Rear: 20 x 8.5 inches

• Tires: 255/30 R20

Standard Wheel Size (S5 Cabriolet):

• Front & Rear: 19 x 8.5 inches

• Tires: 255/35 R19

Optional Wheel Size:

• Front & Rear: 20 x 8.5 inches

• Tires: 255/30 R20