303 XPLR TECH DEEP DIVE

The progression of race speeds

Gravel is getting faster. Every year, both elite and amateur athletes go farther and faster. Pictured here are the winning times from Unbound Gravel starting in 2006. You can see dips of the average speed in some years which were caused by slow, muddy conditions, but in general the race is getting faster with average speeds above 32kph. From the beginning of the development of 303 XPLR in 2021, we knew the fastest gravel wheel needed a truly aerodynamic profile that complemented tires big enough for gravel. We needed a wheel built for speed.

With its 32mm internal width and 54mm deep rim profile, the 303 XPLR achieves speed through measurable gains in Aerodynamics, Vibration Loss, Control, and Durability.

The aerodynamic gains found in our wind tunnel testing are attributed to the overall design concept of the 303 XPLR: identify the right tire sizes and design a rim around those tires.  In the image above, you can see how the wide rim complements big tires to make an unbroken aerodynamic profile.

On the left, we have the dimensions for 303 XPLR and on the right we have the dimensions of what many gravel athletes are racing on today. The difference is clear: wider rim allows for a seamless transition from tire to rim.

What is vibration loss?

When you encounter a bump while riding, your speed is converted into an upward displacement that lifts the rider and bike’s entire mass up and over the bump. In physics terms, this would be described as kinetic energy converting into potential energy. A portion of the potential energy gets converted back into speed as you roll down the back side of each bump, but less than 100%.

This is because the system is damped; the collision force of the tire against each bump is greater than the restitution force of the rebounding tire on the back side of each bump. The result is a net loss of energy which demands additional power from the rider to maintain speed.

In short, it takes more power to go the same speed on rough terrain than it does on smooth terrain.

How do we test?

At our facility in Indianapolis, we test all our products on the Rolling Road. The Rolling Road is a large treadmill that we can modify to simulate different surface conditions, from Roubaix cobbles to velodrome boards. For 303 XPLR, we set up the road speed to 32kph and we vary tire pressure and/or surface conditions to see how a rider’s power requirement changes.