FLO Gravel Wheel Design #12 The A2 Wind Tunnel Results

From an aerodynamic perspective, the wind tunnel is the ultimate test of any product. Our goal was to show that a gravel wheel with gravel tires could be aerodynamic and this was the test that would prove it.

We tested the FLO G700 and FLO G650 against traditional gravel wheels. Traditional gravel wheels are low profile compared to the FLO G700 and FLO G650, which are deeper wheels with an aerodynamic profile specifically designed for gravel riding and tires—a first in the world.  For testing, we compared a Mavic Open Pro to the FLO G700 and a DT Swiss rim against the FLO G650.  We also tested different tires on the rim, described below:

In CFD, the FLO G700 was optimized with a WTB Riddler 37c tire. We chose this as the tire to use for rim comparison. We also tested other tires to compare on the FLO G700.

• Continental GP 5000 32mm
• Maxxis Rambler 40c
• Panaracer Gravel King SK 43c

The FLO G650 was optimized in CFD using a WTB ByWay 47C. We chose this tire for rim comparison. We also tested other tires on the FLO G650.

• WTB Horizon 47c
• Panaracer Gravel King SK 48c

For accurate results, you need a testing protocol. Small changes can have a large effect on the outcome, especially in a wind tunnel. For example, different tire pressures or different tires can change the results. Tires have different molds and each mold produces different results, so a testing protocol helps ensure these items remain consistent.  See below for our testing protocol:

1. Before testing the wheels in the wind tunnel, we run a tare run. This allows us to calculate and compensate for the drag caused by the fixture used to hold the wheels in place. This “tare value” is then removed from future tests so we have accurate aero results.
2. Then, we set tire pressures for each wheel using an Ashcroft pressure sensor. This allows us to set the pressures within 0.1% and make it repeatable. Over the years we’ve learned that removing a pump from a valve can result in a 5psi loss. We use a specially designed valve that allows us to close the valve and prevent air loss when the pump is removed.
3. Once the wheel was mounted in the wind tunnel and the fans were turned on, each wheel was swept from 0-20 degrees of yaw, in 2.5 degree increments.
4. A measurement at each yaw angle was taken twice and averaged.
5. This was repeated with the differences mentioned above, but we make sure same tires and tire direction is used for each test when comparing one wheel to another.

In 2015, we built a computer that mounted to the front of a bike we rode in multiple riding scenarios and collected over 100,000 data points. These data points taught us how a cyclist interacts with the wind when riding and what percentage of time they spend at each yaw angle.

In the wind tunnel, we measure the coefficient of drag (CdA) produced by the wheel at each yaw angle. Using this value and making the assumption that a cyclist is traveling at a relative velocity of 22mph, we calculate the number of watts the wheel produces at that yaw angle.

Since we know the average time a cyclist spends at each yaw angle and the watt value for each yaw angles, we can calculate the average watt value for any given wheel.

The results we receive at the wind tunnel are an important part to the whole development of the wheel. It gives us the aerodynamic part, but for these wheels, we also considered rolling resistance. These add up to Total Power, or a measurement of the number of watts it takes to overcome aerodynamic drag and rolling resistance. The wind tunnel tells us the number of watts consumed by aerodynamic drag. The lower the number, the better. If we’ve done our job, the wheel will consume fewer watts than an OE wheel.

The FLO G700 shows a 5.88 watt reduction per wheel.

The FLO G650 shows a 5.08 watt reduction per wheel.

The following shows the aerodynamic watts consumed by the following tires on the FLO G700. As you can see, the Continental GP 5000 consumed the least amount of watts. But if you’re looking something with more tread, you’ll want to move towards the WTB Riddler 37c.

The following shows the aerodynamic watts consumed by the following tires on the FLO G650. As you can see, the WTB Horizon 47c consumed the least amount of watts.

From the data, we are able to determine how many aerodynamic watts are saved using a FLO G700 and FLO G650 and we can estimate your time savings.  It’s important to understand that the time savings here are only considering half of the equation, the aerodynamic part, and not the rolling resistance improvement we’ve found with our wide internal rim width. So, you can expect time savings to be more when both are considered.

The FLO G700 and FLO G650 are the world’s first aero gravel wheels. It’s been a long process to develop these wheels but we are thrilled with the results. We hope you enjoy them as much as we do.