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Gravel Gear

Swiss Side publishes wind tunnel results for gravel tires

Schwalbe, Continental, WTB, Vittoria, and Panaracer gravel tires measured for aero drag in German wind tunnel.

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In conjunction with the launch of its two new gravel wheelsets, Swiss Side published a detailed report on the aerodynamic drag of several, popular gravel tires at different speeds.

In this cool report, Swiss Side first explains the basic efficiency splits of aero drag and rolling resistance for road bikes versus gravel bikes. (Surprise, gravel bikes have more rolling resistance and more aero drag!)

Related: 24 gravel tires lab tested for speed

Next, Swiss Side shows the aero differences between a ‘bad’ gravel set up and a ‘good’ one, using its own Gravon 250 and Gravon 420 wheels as examples. The numbers refer to the rim depth. Compared to the ‘good’ setup (a 420 with 35mm Schwalbe G-One Speed tire) the ‘bad’ setup (a 250 with a 45mm  G-One Allround) has an aero-drag cost of 1.8 watts at 30kph, 3w at 37.5kph, and 5.4w at 45kph on a still day.

Swiss Side goes further and examines the difference on a windy day.

For their testing, Swiss Side has for years used the GST wind tunnel in Germany. As a journalist, I’m a fan of the brand because of the open access company co-founder Jean-Paul Ballard and his team allow. In 2016, for instance, they let me test some ideas about aero helmets in the tunnel, and they are always up for sharing data and exploring ideas.

Swiss Side co-founder Jean-Paul Ballard is a former Formula 1 engineer.

But back to the windy day performance; Swiss Side measured the benefit of the taller wheels with skinnier tires to be between 5 and 20w at 30-45kph speeds.

Running a model of the Unbound Gravel 200 course, Swiss Side claimed that even the smallest 5w savings could result in an 8.5-minute faster overall time.

Perhaps the most interesting piece of the Swiss Side report was the aero-drag testing done on Schwalbe, Continental, WTB, Vittoria, and Panaracer gravel tires.

Using a Cervélo Aspero gravel bike with the Swiss Side Gravon 420 wheels, Swiss Side tested multiple widths of Schwalbe G-One Allround and Continental TerraSpeed tires. One main takeaway: the bigger the tire, the more aero drag they generated. Also, the 35mm Continental proved to be just a fraction of watt faster in aero drag than the 35mm Schwalbe.

In testing the Schwalbe, Continental, WTB, Vittoria, and Panaracer gravel tires for aero drag, Swiss Side found that the more knobs the tire had, the more drag they generated, underlying one of the many tradeoffs in bike technology. (You can’t have it all, folks!) Looking at only 35mm widths, the knobby Panaracer Gravel King was the slowest, while the slick Schwalbe G-One Speed was the fastest.

Aerodynamics of course is just one piece of the tire-speed puzzle. VeloNews recently completed a lab test of rolling resistance for 24 models of gravel tires at Wheel Energy in Finland. Join VeloNews today to read the full results of that test.

This is just one of many gravel-tire studies Swiss Side published on its site.