Why fat tires are actually faster for gravel racing

Tires in gravel racing keep getting bigger. In fact, some of the fastest riders are ditching traditional gravel tires altogether and switching to mountain bike tires. Why? Because they believe they’re faster.
Wait, what? How could a fat mountain bike tire with big, chunky knobs possibly be faster than a sleek, narrow gravel tire?

Testing wide tires vs. narrow tires

To put this to the test, US Lifetime athlete Dylan Johnson took a bunch of different tires to Silverstone’s pedaling efficiency rig. This machine measures how much power is lost as energy moves from the pedals through the bike and into the road. The goal? Figure out what the optimal tire size is for both road and gravel racing.

Now, before we get into the results, let’s get one thing straight: there’s no single best tire for every situation. Gravel racing is complex and so is tire choice. But if you’re here for a straightforward answer, here it is—bigger tires roll faster on rough terrain.

The surprising results

When testing on pavement, narrower gravel tires (around 35mm) were the fastest, no surprise there. But once the test moved to a rougher surface, something weird happened—mountain bike tires started winning.
At 36 km/h, the fastest tire on cobbles wasn’t a gravel tire at all. It was a 2.2” mountain bike tire.
At this speed, the narrowest gravel tire (35mm) lost nearly 42 watts due to rolling resistance. Meanwhile, the mountain bike tire lost only 8 watts—a massive difference. Even at higher speeds (40 km/h), the mountain bike tire was still the best on rough terrain, although the advantage was smaller.

So, why does this happen?

Why fat tires are faster on gravel

According to Johnson, it all comes down to three things:
Rolling resistance: The bigger the tire, the less it sinks into loose surfaces. Narrow tires cut into the ground and waste energy, while wide tires float and roll more smoothly.
Lower vibration loss: Rough roads create vibrations and vibrations slow you down. Wider tires absorb those bumps, keeping you moving forward instead of bouncing up and down.
Casing thickness: Mountain bike tires can get away with using a thinner casing without increasing puncture risk, which actually makes them roll faster. Most gravel tires don’t do this.

Dylan explains it like this:

“Every time you feel vibration, energy is being wasted as the bike goes up and down instead of forward. Not feeling the vibration is actually a good thing—even if it doesn’t feel faster.”

It’s like driving an old, beat-up car at 100 km/h versus a smooth luxury car. The old car feels faster because of all the rattling and shaking. But in reality, the smooth ride is actually covering ground more efficiently.

What about weight?

Some riders avoid big tires because they think they’ll be too heavy. But the weight penalty is minimal. In Dylan’s test, switching from a 35mm gravel tire to a 2.2” mountain bike tire added about 450 grams total. In real-world riding, that weight difference only costs you about 2 watts on a steep climb—while saving you way more than that on rolling resistance.
So if you’re worrying about weight before considering rolling resistance or aerodynamics, you’ve got it backwards.

What this means for gravel racing

Does this mean everyone should ditch gravel tires entirely? Not necessarily. If your race has a ton of pavement or high-speed sections, a narrower tire might still be best. But for most gravel courses—especially rough ones—wider tires are a clear advantage.
And this isn’t just one test proving it. More and more top gravel racers are making the switch and they’re winning races doing it.
At the end of the day, tire choice is all about trade-offs. But if you’re serious about speed, don’t assume that narrower is always better. It’s time to start looking at real-world performance—because the data is clear: fat tires are fast.