Here’s a bold statement: the age-old belief that wider gravel tires are always faster might be more myth than reality. But here's where it gets controversial—recent tests reveal that the relationship between tire width, aerodynamics, and rolling resistance is far more complex than we thought. And this is the part most people miss: while wider tires often reduce rolling resistance, they can significantly increase aerodynamic drag, potentially negating any speed gains. Let’s dive into the details and uncover why this matters for your next gravel ride.
The conventional wisdom, championed by pros like Dylan Johnson, suggests that wider tires are faster. This idea gained traction after studies on road tires showed that wider options, up to 40mm, offered speed advantages. However, these studies primarily focused on rolling resistance, ignoring the aerodynamic implications of wider tires. Here’s the kicker: wider tires present a larger frontal area, making them less aerodynamic, which can offset their rolling resistance benefits.
To test this, we conducted a comprehensive study using the Vittoria Terreno Dry (now T-30) tires, ranging from 31c to 2.4” (61mm). We excluded sizes below 37mm for practicality, as most gravel riders aren’t considering such narrow options. Vittoria’s recent switch to a T-Score system added a wrinkle, but we adapted by focusing on as-fitted sizes.
Our testing methodology included both wind tunnel and pedaling efficiency rig (PER) tests. For aerodynamics, we tested bike-only setups to isolate tire shapes, using different sidewall colors for clarity. Rolling resistance tests standardized casings where possible, though the 2.25” (57mm) and 2.4” (61mm) tires used Vittoria’s ‘XC Race’ casing, which differs from the ‘Gravel Endurance’ casing used in smaller sizes. This casing difference may have influenced results, but the data remains enlightening.
In the wind tunnel, we tested yaw angles from -15º to +15º at 35km/h, a speed reflective of pro gravel races. We used two wheelsets: Zipp 303 XPLR NSWs (32mm internal width) and Hunt 40 CGRs (25mm internal width). Tyre pressures were set using SRAM’s online calculator, and we repeated tests to ensure accuracy.
For rolling resistance, the PER at Silverstone simulated three surfaces: smooth tarmac, setts (gravel analogue), and large cobbles. We tested a Lauf Seigla bike on the rear wheel only, multiplying results by 1.818 to account for weight distribution. New cassettes and chains ensured consistency, and we ran 60-second tests at 25km/h and 35km/h for each tire size and surface.
Here’s the surprising part: MTB tires (2.25” and 2.4”) showed significantly lower rolling resistance than gravel tires, even when accounting for aerodynamic drag. This challenges the notion that wider gravel tires are always faster, suggesting that MTB tires might be the superior choice for speed-focused riders.
However, it’s not all about speed. Grip, puncture resistance, and ride feel are equally important. While MTB tires offer better control and fun on rough descents, they’re heavier and less agile on roads. The question remains: should you prioritize speed or versatility?
For bike design, this data hints at a future where MTB standards replace road standards in gravel bikes, allowing for larger tires and better mud clearance. But for now, choosing the right tire size involves balancing lab data with real-world practicality.
Thought-provoking question: Are we sacrificing too much in handling and versatility by chasing marginal speed gains with wider tires? Share your thoughts in the comments—let’s spark a discussion!
