Lessons from the windtunnel

Along with the folks from SwissSide we spent some time in the windtunnel testing gear and position. In the first of a three-part series, a look at the best position for descending.

| July 23, 2018 | GEAR

How much difference does an aggressive position make when you are descending? We hit the wind tunnel to find out.

How much difference does an aggressive position make when you are descending? We hit the wind tunnel to find out.

Photo >Kevin Mackinnon / spomedis

It is fresh here - just 16 degrees Celsius, which isn't too bad until the air is accelerated to 45 km/ h as it goes past you. Thanks to an invitation from Jean-Paul Ballard from Swiss Side, we're here in Immenstaad, Germany, where triathlon stars like Patrick Lange and Jan Frodeno have worked on their aero positions.

Immediately after the Eurobike, we accepted the invitation from Swiss Side to the wind tunnel that's part of the Airbus development area - of course with all sorts of aerodynamic tests in mind. Are modern triathlon bikes faster with our without hydration? How much time do you lose with a water bottle between your aero bars? What is the optimal head position? Here comes part 1 of our tests: What is the best position for descending?

The bike is clamped to a balance that registers all kinds of data with extreme sensitivity.

The bike is clamped to a balance that registers all kinds of data with extreme sensitivity.

Photo >Kevin Mackinnon / spomedis

Getting aero on descents

We've all watched the pros tuck when they're descending. Once they hit downhill speeds above 50 km / h, some athletes stop pedaling, grab the base bar, make themselves small and lay their buttocks on the top tube (see photo below). How much of a difference does this position make in terms of aerodynamics? A lot. It's extremely aerodynamic.

For one of our test riders, this position brought savings of 66.2 watts compared to the baseline (front-facing in the aero position). In a second rider, who had a lower CdA value than driver 1, there was a saving of 29.8 watts. This position is better aerodynamically, but you're also getting that extra speed while giving your legs a break.

That said, we can't recommend this position for everyone. All the speed gains in the world won't help if you are on the side of the road. Riding like this is incredibly dangerous. A bump on the road can send you off the bike or cause other trauma (remember, for guys, certain sensitive parts are on the top tube of the bike). A firm grip is mandatory and holding this position requires not only courage, but also good muscle strength  and a high degree of concentration.

Conclusion: Even if you save valuable watts with this position, inexperienced and insecure cyclists should avoid it.

This descending position markedly reduces aerodynamic drag.

This descending position markedly reduces aerodynamic drag.

Photo >Kevin Mackinnon / spomedis

More stories to come from our testing in the wind tunnel.