Upgrade Your S3 Brakes: TTS Disc Swap?

For many Audi S3 owners, the pursuit of optimal performance extends beyond engine tunes and suspension upgrades; it inevitably leads to the braking system. A common frustration is the dreaded brake judder, especially under heavy braking, which not only compromises safety but also detracts significantly from the driving experience. This often leads enthusiasts to explore alternative solutions, and one increasingly popular option gaining traction is the use of Audi TTS front brake discs on the S3. But is this a viable, beneficial, and straightforward swap? Let's delve into the specifics of why S3 owners are considering this alternative and what you need to know before making the switch.

Why Consider Audi TTS Front Discs for Your S3?

While the Audi S3 typically comes equipped with 345mm front brake discs, the Audi TTS, a close relative in the VW Group family, often features 340mm discs. At first glance, a smaller disc might seem like a downgrade, but for many S3 owners, this slight difference in diameter offers several compelling advantages that address common issues with the standard setup.

Addressing the "Rust Lip" Phenomenon

One of the most frequently cited reasons for considering the 340mm TTS discs is to combat the notorious "rust lip" that can form on the outer edge of the larger 345mm S3 discs. This occurs because the brake pads on the 345mm setup don't always sweep the entire disc surface, leaving a small, unworn, and consequently rust-prone lip around the circumference. This rust lip can be unsightly and, over time, potentially lead to uneven wear or even contribute to noise. By fitting 340mm discs, which are only marginally smaller, the brake pads are designed to sweep the entire surface more effectively, thereby eliminating or significantly reducing the formation of this unsightly and problematic rust lip. This ensures a cleaner disc appearance and more uniform pad wear.

Weight Reduction Benefits

In the world of performance cars, every gram counts, especially when it comes to unsprung weight – the weight not supported by the car's suspension. Brake discs are a significant contributor to unsprung weight. Since the 340mm TTS discs are slightly narrower and smaller in diameter than their 345mm S3 counterparts, they inherently weigh less. While the individual weight saving per disc might seem minor, when multiplied by two front discs, the cumulative reduction in unsprung mass can subtly improve handling dynamics. Reduced unsprung weight allows the suspension to react more quickly and effectively to road imperfections, potentially leading to better ride quality and improved grip, particularly over bumpy surfaces. It's a small but tangible gain for those seeking to optimise their vehicle's performance.

Enhanced Cooling Slot Design

Another often overlooked, but crucial, aspect of brake disc performance is cooling. Efficient heat dissipation is vital to prevent brake fade and maintain consistent braking performance, especially during spirited driving or track use. The user feedback highlights that the cooling slots on some TTS discs are open at the hub end, rather rather than just the outer edge. This design difference can significantly improve airflow through the disc's internal vanes, leading to more efficient heat expulsion. Better cooling means the discs are less likely to overheat, reducing the risk of brake fade and maintaining consistent bite, even under sustained heavy braking. This is a significant advantage for drivers who push their vehicles hard and demand reliable braking performance.

Battling the Dreaded Brake Judder

Brake judder, felt as a vibration through the steering wheel or brake pedal during braking, is a common and highly irritating issue. The user's experience with "terrible problems with judder on 2 sets of Pagid discs and pads under heavy braking" underscores the importance of disc and pad quality, as well as proper installation. Conversely, their positive experience with Brembo discs and pads highlights that not all components are created equal.

Common Causes of Brake Judder

Understanding the root causes of judder is key to preventing it:

• Disc Thickness Variation (DTV): This is the most common cause. It occurs when the disc's thickness varies around its circumference, causing the pad to 'grab' more at thicker points and release at thinner points. DTV can be caused by improper installation, excessive heat, or poor manufacturing tolerances.
• Lateral Runout: This refers to the side-to-side wobble of the disc as it rotates. Even a tiny amount can cause the pads to be pushed back and forth, leading to judder. This is often caused by debris or rust between the hub and the disc, or a bent hub flange.
• Overheating and Hot Spots: Excessive heat can cause the disc material to change its metallurgical structure in certain areas, creating hard spots. These areas have different friction characteristics, leading to uneven braking and judder.
• Improper Pad Bedding: If brake pads are not properly bedded in, material can be unevenly deposited onto the disc surface, leading to variations in friction.
• Poor Quality Components: As the user noted, some brands may simply not hold up to heavy use or have inconsistent manufacturing quality, making them more prone to judder.

The Importance of Hub Preparation

The user wisely emphasises: "It is essential that the hubs are cleaned and any rust etc is removed before fitting the new discs so they sit totally flat. Any imperfection will lead to judder as well." This point cannot be overstated. Even a minuscule piece of rust, dirt, or old grease on the hub face can cause the new brake disc to sit at a slight angle. This seemingly minor misalignment, when multiplied by the rotational speed and clamping force of the calipers, translates into significant lateral runout and immediate judder. Proper hub preparation is the absolute foundation for a smooth, judder-free braking experience.

Installation Considerations and Best Practices

While the swap from 345mm S3 discs to 340mm TTS discs is considered a popular and generally straightforward modification, proper installation is paramount to ensuring optimal performance and longevity, particularly to avoid judder. The fact that "Brembo discs are not available on ECP in 345mm but they are there in 340mm" further supports the practicality of this alternative, offering a premium brand option that might otherwise be unavailable for the standard S3 size.

Pre-Installation Checklist:

1. Component Quality: Invest in high-quality discs and pads. As the user's experience suggests, brands like Brembo have a strong reputation for reliability and performance, whereas others may fall short under demanding conditions.
2. Tools: Ensure you have the correct tools, including a torque wrench, wire brush, brake cleaner, and potentially a hub cleaning tool.
3. Safety First: Always use axle stands and ensure the vehicle is stable before working underneath it. Wear appropriate personal protective equipment.

Step-by-Step Hub Cleaning:

This is the most critical step for preventing judder:

1. Remove Old Disc: With the wheel off and caliper unbolted and secured (not left hanging by the brake hose), remove the old brake disc.
2. Inspect Hub Face: Carefully inspect the hub mounting surface. It should be perfectly flat and free of any rust, corrosion, old brake pad material, or debris.
3. Wire Brush: Use a stiff wire brush to thoroughly scrub the entire hub face where the disc mounts. Pay close attention to the centre bore and the wheel stud holes.
4. Hub Cleaning Tool (Optional but Recommended): For best results, consider using a dedicated hub cleaning tool that attaches to a drill. These tools are designed to quickly and effectively remove all surface corrosion without damaging the hub.
5. Brake Cleaner: Once physically cleaned, spray the hub generously with brake cleaner and wipe it thoroughly with a clean rag. This removes any remaining dust, grease, or residue. The hub must be spotless and completely dry before the new disc is fitted.

Fitting the New Discs and Pads:

1. Handle with Care: New discs often come with a protective anti-corrosion coating. While some manufacturers recommend cleaning it off, others state it will burn off during the first few stops. Follow the manufacturer's instructions. Avoid touching the disc surface with bare hands as oils can cause hot spots.
2. Mount Disc Flat: Carefully slide the new disc onto the clean hub. Ensure it sits absolutely flush against the hub face. Use a lug nut or two to temporarily hold it firmly in place while you reassemble the caliper.
3. New Pads: Always fit new brake pads with new discs. Ensure caliper pistons are fully retracted (using a proper tool) and that the pads sit correctly in the caliper carrier.
4. Torque Everything: Reinstall the caliper and wheel bolts, tightening them to the manufacturer's specified torque settings using a torque wrench. Do not overtighten.
5. Bedding In: This is crucial. Follow the brake pad manufacturer's recommended bedding-in procedure. This typically involves a series of moderate stops from increasing speeds, allowing the brakes to cool between cycles. Proper bedding ensures an even transfer layer of pad material onto the disc, optimising performance and preventing judder.

Performance Implications of the 340mm Swap

While the 340mm discs are only slightly smaller than the 345mm standard S3 items, it's worth considering any potential performance implications. In most street driving scenarios, the difference in braking performance will be negligible to imperceptible. The key benefits of reduced unsprung weight, better cooling, and the elimination of the rust lip will likely outweigh any minimal reduction in swept area.

For track use, the improved cooling design of the TTS discs could actually be a significant advantage, helping to maintain consistent braking performance over extended periods. The slight reduction in disc mass also means less rotational inertia, which can lead to a marginally quicker acceleration and deceleration response.

It's important to pair the 340mm discs with high-quality, performance-oriented brake pads. The synergy between a good disc and a complementary pad is what truly defines braking performance. Don't compromise on pads just to save a few quid; the overall system is only as strong as its weakest link.

Comparative Table: Audi S3 (Standard) vs. Audi TTS (Alternative) Front Discs

Frequently Asked Questions (FAQs)

Q1: Is this swap a direct bolt-on for the S3?

A1: Yes, the 340mm TTS discs are generally considered a direct bolt-on replacement for the 345mm S3 discs, as the caliper carrier and mounting points are compatible. However, always double-check specific part numbers and fitment guides for your exact S3 model year.

Q2: Will using 340mm discs affect my braking performance negatively?

A2: For typical road use, any negative impact on braking performance is likely to be negligible. The slight reduction in swept area is often offset by benefits like improved cooling and better pad sweep, potentially leading to a more consistent and judder-free experience. For extreme track use, some might prefer the larger swept area of 345mm if they can find high-quality, judder-free discs.

Q3: Do I need new calipers or caliper carriers for the 340mm discs?

A3: No, you should be able to retain your existing S3 calipers and caliper carriers. The small difference in disc diameter is typically accommodated by the existing caliper setup.

Q4: What brake pads should I use with the 340mm TTS discs?

A4: You should use brake pads designed for the S3 345mm caliper, as the caliper itself remains unchanged. The key is to select high-quality pads that complement your driving style and the new discs. Based on the user's experience, Brembo pads could be a good starting point.

Q5: How important is brake disc bedding-in?

A5: Extremely important! Proper bedding-in is crucial for optimising brake performance, achieving full stopping power, and preventing judder. It ensures an even transfer layer of pad material onto the disc surface, which is vital for consistent friction and heat management. Always follow the manufacturer's specific bedding-in procedure.

Q6: Can this modification affect my car's warranty?

A6: Any modification to a vehicle can potentially affect its warranty, especially if the modification is deemed to have caused a fault. It's always advisable to consult with your Audi dealer if you have concerns about warranty coverage before making significant changes to your braking system.

Conclusion

The decision to fit Audi TTS 340mm front brake discs to your S3 appears to be a well-researched and popular option amongst S3 owners seeking to mitigate common issues like brake judder and the formation of the unsightly rust lip. The benefits of reduced unsprung weight and potentially superior cooling slot design further bolster its appeal.

However, the success of this, or any, brake system overhaul hinges critically on two factors: the quality of the components chosen and the meticulousness of the installation. As highlighted by the experiences shared, opting for reputable brands like Brembo can make a significant difference in preventing judder, and the absolute necessity of thoroughly cleaning the hub face before disc installation cannot be overstated. Any shortcuts here will almost certainly lead to frustration.

While this article provides a comprehensive overview, as with any vehicle modification, it is always wise to conduct your own additional research specific to your exact Audi S3 model year and driving requirements. Engaging with fellow S3 enthusiasts on forums can provide valuable real-world insights. By combining high-quality parts with diligent installation, swapping to 340mm TTS discs could indeed provide your S3 with the smooth, consistent, and reliable braking performance you desire.

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