The conventional wisdom about gravel tires is that wider is faster. But is it that simple? We set out to explore this belief, inspired by professional riders like Dylan Johnson and the trend of pushing clearance limits on pro bikes. Our previous studies on road tire width supported this notion, but we wanted to delve deeper into the specifics of gravel tires.
Our investigation focused on rolling resistance and aerodynamics. We selected the Vittoria Terreno Dry model, ranging from 31c to 2.4" (61mm), for a comprehensive test. We standardized the casings, using Vittoria's 'Gravel Endurance' for most sizes and 'XC Race' for the larger MTB-style tires. This setup aimed to reduce the 'drum effect' on the rolling resistance rig, ensuring accurate measurements.
However, a crucial aspect often overlooked is the increased frontal area of wider tires, which can negatively impact aerodynamics. To address this, we conducted aero testing in a wind tunnel, using a bike-only setup to minimize variables. We tested various widths on two sets of wheels: Zipp 303 XPLR NSWs with a wide 32mm internal width and Hunt 40 CGRs with a more standard 25mm internal rim.
The results were intriguing. On all surfaces, rolling resistance increased with width until we reached the MTB-style tires, which surprisingly exhibited lower rolling resistance. This contradicted our initial assumption that wider tires would reduce rolling resistance, especially on rough terrain. The data also revealed that the differences in tire performance were more significant than those caused by aerodynamics, with variations reaching 43 watts between the fastest and slowest setups.
When combining the aero and rolling resistance data, we found that for gravel tires, going as narrow as possible is generally faster, except on extremely rough terrain where wider tires excel. The exception to this rule was the MTB-style tires, which were significantly faster even with their additional aerodynamic drag. This finding challenges the conventional wisdom and highlights the importance of tire construction.
The construction of the tires played a pivotal role in performance. Vittoria's 'Gravel Endurance' and 'XC Race' casings had different thread counts and designs, impacting rolling resistance. This suggests that tire construction, not just width, is a critical factor in performance. The data also revealed that the 'XC Trail' casing, with its 60-TPI nylon, might have been a closer match to the gravel models, but further testing is needed to confirm this.
Our findings also raise questions about the applicability of our previous tests. In 2025, we found that wider tires were faster, but this may have been influenced by construction differences, especially for the 2.1" size. In 2026, we tested 'T30' models, which could have had construction tweaks compared to the 'Terreno Dry' tires from 2025. These nuances highlight the complexity of tire performance and the need for comprehensive testing.
So, should you fit MTB tires to your gravel bike? The data suggests yes, but it's not that straightforward. MTB tires are likely made more supple than gravel options, which could explain their superior performance. However, we tested only one tire model, and further research is needed to confirm broader market trends. Additionally, this advice might not be practical for all riders, as many gravel bikes can barely accommodate 2.1" or 2.25" tires.
The implications for bike design are significant. As gravel racing gains popularity and professionalism, the industry is focusing on performance. Fitting extremely large MTB tires to gravel bikes offers clear wattage gains, but it's limited by road standards. Many new gravel bikes can fit 2.1" or 2.25" tires, but there's a growing need for designs that accommodate larger volumes. MTB standards, with wider bottom brackets and boost-spacing rear wheels, could be the solution, allowing for bigger tires while maintaining mud and stone clearance. This shift might cause some initial resistance, but it's a logical step towards the industry's goals.
In conclusion, while wider gravel tires are often believed to be faster, our findings reveal a more nuanced picture. Tire construction and width both play crucial roles in performance, and the ideal setup depends on various factors, including terrain and rider preferences. This research underscores the importance of comprehensive testing and highlights the potential for further advancements in gravel bike design and tire technology.
