Positioned for Speed Course

Positioned for Speed Course

It's been a few months since PowerTap announced its partnership with Retül and Alphamantis in support of the Positioned for Speed Course that sees Retül fit philosophy paired with the Alphamantis track aero system and PowerTap power meters to optimize a riders position for...well, speed of course.

I made a trip out to ERO Sports (pronounced Aero) at the VELO Sports Center in LA for the second edition of the course June 3-4. I attended the first course in December of last year as well to help support the use of our equipment and see everything first hand. After leaving the LA after the first course, I was curious to say the least.

Observers check my data while I ride by in the Velodrome.

In addition to being a PowerTap product manager and having vested business interest in something that uses our products in a unique and valuable way (more on that later) I am a passionate cyclist and triathlete who enjoys going fast on a bike. So to say I wanted to get myself optimized would be an understatement, a big one. Luckily for me, I knew the guy who picks the subjects for the course (thanks Andy) and offered myself up for testing. This was a great opportunity to see the process first hand. I didn't doubt that it worked, but nothing can be more convincing that actually doing it.

It's no big secret that aerodynamic drag is the biggest obstacle a cyclist needs to overcome. The fight against the wind, if you will, has spawned an entire sub-market of products that promise to shave seconds and minutes. Some actually do but there is a lot of marketing fluff going on too, and it's really difficult to weed out the garbage. For the last 2+ decades cyclists have gone to the wind tunnel to improve their position and test equipment. I've spent some time in a wind tunnel and found it to be a valuable experience, but unless you have deep pockets or a sponsor backing your cause its cost prohibitive.

Here is where I shamelessly plug the Alphamantis track aero system, which is in a lot of ways better than the wind tunnel because what they have found is that when you are actually moving on your bicycle you move in ways that you wouldn't when stationary, and that can have significant effects on drag. The other reason is simple: value. The cost of wind tunnel testing is exorbitant, ranging up from $400 per hour. There is also the question of repeatability from one wind tunnel to the next. I have read reports that the differences between wind tunnels can be significant. The Alphamantis testing system has limited the variables right down to air density ensuring consistent measurement from test to test over long periods of time and geographic location.

The order of the day was to get me in the most aerodynamic position I could handle for an Ironman distance race. The process is pretty straight forward: 1) Baseline; 2) Test; 3) Optimize; 4) Repeat steps 2 and 3.

The first step is to baseline your current position using the Retül Vantage 3D Motion Capture System, which measures rider movement in 3D while pedaling and includes their Zin tool for really accurate bike measurements. Having a dozen certified Retül fitters overseeing the process makes things really interesting as I got an immediate second opinion and third...and fourth... and so on... I was lucky enough to be in a relatively efficient position already and had little tweaking to do before heading down to the track for testing.

Baseline position measurements using Retül Vantage 3D motion capture.

Once down on the track there are a series of multiple lap runs performed using a PowerTap hub-based power meter and the Alphamantis track aero system, which is a very sophisticated timing system and software that uses power meter data and speed to calculate drag (CdA). This is a gross oversimplification of what it actually does but I don't want to misrepresent myself as an expert of the Alphamantis system as there is a lot that goes into it. The piece that I can speak to is the importance of accurate, reliable power measurement and the reason Alphamantis has chosen the PowerTap hub as their go to power meter.

Baseline test in normal road kit and helmet.

All things being equal, measuring power at the hub is best for quantifying how much energy is being delivered to the road, which is exactly what is required for aero testing as any drivetrain inefficiencies do not come into play. For the gearheads out there, it is like the difference between measuring HP at the crank (engine) or at the wheel; there is always a difference as any machine with moving parts involves friction (bad). The other reason is true torque isolation. Bicycle power meters are designed to do one thing, measure linear torque. Couple that with an angular velocity component (let's call that speed) and voilà, you have power.

The design of the PowerTap hub is essentially a hub within a hub where the inner hub contains the torque measuring sensors (strain gauges) and is completely isolated from all the other non-linear forces put on the wheel, which is not a feature present when measuring power at other locations on the bike. Don't get me wrong, there are a lot of other capable, non-hub based power meters out there, but for this particular application the PowerTap hub is king.

Final test in skinsuit and aero helmet with shrug.

After about an hour and seemingly countless laps around the track, I had a new position and lowered my CdA by roughly 0.02, which may not seem like a lot, but represents minutes in time savings over the course of an IM bike leg. I will take free speed whenever I can. Over the next hour I tested a few different helmets and a skinsuit and was able to get another 0.02 improvement in CdA. At the end of the day I saw a drag reduction that could save me 18 watts, or around 12 minutes of time for 112 miles — which is huge when you consider most people train hundreds of hours to get the same benefit. I was able to do it in about 3 hours.

Skinsuit and aero helmet test — side profile.

The purpose of me going through the Retül/Alphamantis Positioned for Speed process was twofold: I wanted to be able to speak from experience when telling people about it and, selfishly, I wanted to see what improvements I could make in my position and equipment selection. Now that I have experienced it I wouldn't hesitate to recommend it to anyone serious about performance. The only thing I would say is do it soon, because your competitors will do it eventually — so you'll want to enjoy a little edge for as long as you can.

- Justin Henkel, PowerTap Product Manager




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