Time Trial Observation Part 3: Difference in Air Resistance in the same Bike Position

Hello, this is Saita from LEOMO.

This is part 3 of our time trial prep blog series. In this post I’m going to talk about improving race time by being conscious about maintaining a more aerodynamic position (aero form) while keeping the same bike set up.   

Essentially, time trialling is all about overcoming air resistance, so staying in the “aero form” becomes particularly important. In addition to having a bike setup that already puts you into a streamlined position, actively engaging parts of the body to make yourself smaller (ex. assuming the “aero shrug”) can be highly effective in further reducing the air resistance.

Image 1: Aero Form (Left) vs. Relaxed (Right)

Image 2: Aero Form (Left) vs. Relaxed (Right)

Figure 1: MPI and Ant+ data when relaxed and with Aero Form

Let’s look at the data comparing “when conscious of aero form” vs. “when relaxed” (Fig 1). In an effort to reduce the influence fatigue had on the second trial, I implemented a 30-minute rest period between the two trials.

In both the aero form and relaxed trials I rode on the same course (13.6km), with the same cadence, and holding the power near constant around my FTP.

When I look at the Torso Angle between the two trials, it is 11.8 degrees in the relaxed position and 8.9 degrees when I’m holding the tension in the body to assume my aero form (really focusing on tucking my head and lowering my upper body). The almost 3 degree difference in the two torso angles indicate how much more of my upper body is exposed to the wind when I’m riding in the relaxed position.

Comparing the two trials, I produced an average of 335 watts during the relaxed position and 327 watts in the Aero Form position. In the Aero Form position I produced 8 watts less, but rode 7 seconds faster. So I was able to save energy and still ride faster.

Let’s take a look at the Pelvic Angle. In the relaxed position my Pelvic Angle was 47.8 degrees and it decreased to 47.0 degrees with the aero from. From the Pelvic Angle, one can see that I was trying to really “tuck-in” and lean forward to maintain an aerodynamic position. However, this ‘tucking’ position interfered with my ability to fully articulate my thighs during the pedal stroke, which, in turn, reduced my ability to produce as much power.   

As shown above, even if the bike setup and riding positions are same, the times can be different with the posture of the upper body. Perhaps the most interesting part of the time trial is whether you choose a form that is easy to relax and maximize pedaling power even if the air resistance is high, or a form with low air resistance even if it means slightly sacrificing power.

In this blog, I hope I was able to demonstrate the influence the upper body form has on time-trial performance. Perhaps the most interesting part of the time trial is understanding the trade-offs among assuming a sustainable posture, reducing aero drag, and maintaining maximum power generation.  Time trialing has many components to consider, and that’s just part of the interesting decision making in optimizing the performance.

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