Zenith Tire Testing Update: Sonoma Results, Strategy Takeaways, and What Comes Next

A major part of building Zenith Racing Series is continuing to learn from real race weekends and using that information to refine the competitor experience. As the series grows, we want to be thoughtful in how we evaluate performance, strategy, and the details of the ruleset that shape the racing.

That means putting in the time and resources to gather meaningful information in a live environment, then using it carefully as we continue to develop a competitive, balanced, and enjoyable format for the paddock.

This season, the series has committed to purchasing a BMW G82 that will run at each event for one purpose: collecting useful data for competitors. That work supports two key areas of development within the series. The first is power-to-weight and acceleration compliance data. The second is tire testing and tire strategy analysis in live race conditions.

To support that effort, we have brought in Matt Million and Colin Garrett to drive the BMW, with NineFour Motorsports operating the race team throughout the weekend. The goal is simple: use a consistent platform, strong drivers, and a professional team environment to generate credible information that helps us shape a fair, competitive, and genuinely fun ruleset for everyone in the paddock. Importantly, Matt and Colin are not eligible for year-end awards, as this program exists strictly to support series development and provide useful information back to competitors.

This is also not a one-event exercise. The plan is to continue testing throughout the full season, continue sharing what we learn with competitors, and use that information to refine the rules as more real-world data is gathered across different tracks and conditions.

For Sonoma, that meant putting the car through the three primary tire strategy paths currently available in the series:

• Continental ExtremeContact Force, an endurance-oriented 200tw compound
• Yokohama A052, a softer 200tw option
• Pirelli slick, a high-pace, high-degradation option

Rather than relying on isolated testing laps, we raced each compound throughout the weekend to understand both peak pace and degradation in a real endurance environment. All of the data below has Code 60 laps and in/out laps removed, and traffic was roughly similar across both days.

Sonoma Tire Test Results

Continental ExtremeContact Force
The Continental ExtremeContact Force was run for 319.03 minutes on Sunday. It recorded a fast lap of 1:47.84 and an Hour 1 average of 1:49.14. Its average moved to 1:50.01 from Hours 1-3 and 1:50.52 from Hours 3-5. Based on that trend, the Hour 5-7 average was projected at 1:50.52, producing a total race average of 1:50.18. With no tire changes and no Code 60 tire change time penalty, the strategy projected to 228.71 theoretical laps over 7 hours.

Pirelli Slick
The Pirelli slick was run for 122.85 minutes on Sunday, with driver feedback indicating roughly another 30 minutes was possible before a tire change became necessary due to cording. It delivered the quickest outright pace of the weekend, with a fast lap of 1:43.66, an Hour 1 average of 1:45.29, and an Hour 2 average of 1:46.53. Assuming tire changes at the 2.5-hour and 5-hour marks, the total race average lap projects to 1:45.99. Factoring in 2 tire change penalty laps and 50 seconds of Code 60 tire change time, or roughly 0.47 laps, the strategy projected to 235.29 theoretical laps over 7 hours.

Yokohama A052 — Race Result
The Yokohama A052 was run for the full race distance on Saturday, which in itself was one of the more notable takeaways from the weekend. It produced a fast lap of 1:46.80 and averaged 1:48.30 in Hour 1. Its average settled at 1:49.00 from Hours 1-3, 1:49.04 from Hours 3-5, and 1:50.29 from Hours 5-7. Across the full race, the total average lap was 1:49.28. With no tire changes and no tire change time penalty under Code 60, the strategy projected to 230.60 theoretical laps over 7 hours.

Yokohama A052 — Theoretical Alternate Strategy
We also modeled an alternate, theoretical Yokohama strategy that included a tire stop at the 4-hour mark. In that scenario, the tire would still open with a fast lap of 1:46.80 and an Hour 1 average of 1:48.30, followed by 1:49.00 from Hours 1-3 and 1:49.04 through Hour 4. After the tire change, the model resets to an Hour 5 average of 1:48.30 and an Hours 6-7 average of 1:49.00. That produces a total race average lap of 1:48.81. After 1 tire change penalty lap and 25 seconds of Code 60 tire change time, or roughly 0.24 laps, the strategy projected to 230.35 theoretical laps over 7 hours.

What stood out

One of the takeaways from Sonoma was how strong the Pirelli’s peak pace was, while still maintaining relatively low pace degradation over its usable life. The limiting factor for the slick was not that it fell away dramatically on lap time, but that it eventually approached the end of its usable tread and rubber, showing signs of nearing cording.

The Yokohama behaved in a similar fashion. Its limitation was also tied more to remaining tread and rubber than to any major pace collapse. What was especially notable was that the Yokohama lasted the full 7-hour race at Sonoma. For competitors, that should help illustrate just how low degradation was at Sonoma, because under more typical conditions the tire is usually much closer to a 4-hour tire.

The Continental showed a similar overall degradation shape in that it also gave up pace as the run went on. The Continental degraded at a similar rate in pace as the Yokohama and Pirelli, but did so differently than we expected based on our initial tire testing at Barber and NCM. Overall tread wear looked very good and it appeared fully capable of covering the full race distance from a durability standpoint. What stood out was that the tire still gave up noticeable lap time once it got hot, meaning the Conti showed relatively low tread degradation but more pace degradation than expected.

That distinction matters, because while all three options can complete meaningful race stints, they do so with different tradeoffs in outright speed, durability, and how that performance changes over time.

Sonoma strategy model

Based on the Sonoma findings, we believe that a track that rewards peak pace of softer compound tires needs an increased lap deduction over our current ruleset. Additionally, a track that exhibits very low tire degradation also requires an increased lap deduction over our current ruleset. For Sonoma, we would expect the appropriate tire change deduction to be 1 lap per tire changed after the initial free single tire change, as it exhibits large gains for peak performance of softer compound tires and incredibly low degradation.

Using Sonoma as the comparison point, the strategies would have modeled as follows:

• Continental, no tire change: 228.71 laps
• Pirelli, two tire changes: 229.29 laps
• Yokohama, no tire change: 230.60 laps
• Yokohama, one tire change: 228.35 laps

Based on these findings, we can see that the peak performance delta of the slick versus the 200tw tire was significantly larger than what we found at our Barber Motorsports Park test. Sonoma also appeared to produce very low degradation on the Yokohama, which lasted nearly double its more typical lifespan, extending to roughly seven hours rather than four. The Continental likewise exhibited degradation characteristics that aligned more closely with the Yokohama than we expected, not in tread depth, but in the form of overheating and pace loss that reduced its overall average performance.

Looking ahead, we believe Barber will exhibit more tire degradation than Sonoma based on historical data from the circuit, and our previous testing has shown that the peak performance delta is narrower there, even with a shorter lap. As such, we will be increasing the tire change lap deduction to 2 laps per tire change after the initial free single tire change, up from the current 1-lap deduction.

Just as importantly, this process will continue beyond Sonoma and Barber. We intend to keep testing tire strategies throughout the season, continue publishing those results for competitors, and keep refining the deductions as we better understand how each circuit rewards pace, longevity, and pit strategy. Over time, we expect that work to lead to a track-specific tire change deduction table that more accurately reflects the characteristics of each venue. It is a big investment, but one that we believe strongly aligns with the series vision of creating fair, fun, and competitive race environment.

We will also continue posting updated tire change lap deductions prior to each event in the supplemental rules as the series keeps refining this part of the regulations. The goal is to continue evaluating the available strategies in a real race environment and make adjustments that support close, competitive, and strategically interesting racing for the field.

We are excited about the level of effort being put into the fairness and competitiveness of Zenith Racing Series, and Sonoma was only the beginning of that process. The BMW program, the support from Matt Million, Colin Garrett, and NineFour Motorsports, and the data being gathered throughout the season are all part of a broader investment in building the strongest possible experience for competitors.

For teams interested in trying the series, Barber Motorsports Park on April 25-26 will be the next opportunity, featuring our 5+6H event format. You can also follow along with the series on YouTube at Zenith Racing Series and across our social media channels for more updates, race coverage, and future testing results.