Introduction
At Speeco, our products are not designed based on hype. Instead, every Speeco product is backed by research. Recently a trend is emerging to close the gap between two aerobars to create a single surface. Something we have tested multiple times over the previous 6 years, but never actually tested faster. However, it is also not something we have optimized for. So Zeb set out on a process to 1. Analyse frequent positions. 2. CFD test and optimize the shape of a monobar. 3. Test the optimal shape in the windtunnel at different wind angles and 4. Openly show the whole picture.
Method
Position analysis
Over the last years we have made hundreds of custom aerobar designs based on the athletes positions. From the trend of this data 4 different arm widths in table 1, and the 2 different arm angles in table 2 are derived. The recently published Generic Cycling Model (GCM) from the University of Delft was morphed into these 8 positions to create a case where only the position is different between the tests. For each of these positions, a set of our custom dual TriX aerobars was designed.
| Name | Super-Narrow | Narrow | Neutral | Wide |
|---|---|---|---|---|
| Center-Center Cup width | 105mm | 135mm | 160mm | 195mm |
| Name | Low-Hand position | High hand position |
|---|---|---|
| Arm angle | 20° | 30° |
CFD optimization of monobar design
For all 8 positions, 20 different monobar shapes were iteratively designed, and then CFD tested. (some of these shown below). As a benchmark, our previously CFD- and wind-tunnel-optimized custom dual TriX extensions were used. All of these were tested in a modified version of the Airo CFD software. In each iteration, parameters such as hull shape, depth, and edge radii were adjusted based on the previous result, progressively converging toward the final optimized geometry. In this software, only a 0° windangle can be analyzed. However, in previous confidential testing it was already clear a closed monobar would have it’s maximum effect under 0°.
Windtunnel validation and analysis
In reality, long distance triathlon races are done under a range of wind angles. Some relative windless, but others like Kona are particularily wind-intensive. Therefor it is required to analyse the difference between the dual bars and the monobar under different wind angles. Additionally the CFD simulations have to be validated.
The windtunnel test was conducted at the BikeValley windtunnel in Beringen, Belgium together with Ironman 70.3 Aix-en-Provence winner Michele Bortolamedi. Yaw angles were tested in a sweep consisting of 0°, 5° and 10°. This was combined with his position testing, and because of time constraints only the three elbow position most relevant to Bortolamedi’s position have been included in the test.
For the test a modular setup was developed where the bottom of the aerobar could be replaced by different covers at each width, and therefor have the shape of the actual product while keeping all other parameters identical.
Results
CFD
After optimization of the monobar’s shape, the comparison to the orignal Speeco TriX dual bars, at 0° yaw is visualized in Figure 4. At a negative number (-x) the monobar is x Watt faster than the dual bars. At a positive number, the dual bars are faster by x Watt.
Windtunnel
Using the modular setup, Michelle Bortolamedi’s dragforce was measured in the windtunnel in different positions, with different covers and at a different wind angle (0°, 5° and 10°). At a negative number (-x) the monobar is x Watt faster than the dual bars. At a positive number, the dual bars are faster by x Watt.
Yaw weighted results
Based on an analysis of Michele Bortolamedi’s upcoming goals, a yaw weighting was made to analyse each setup over the complete situation. A comparison of the dual bars and the monobar is visualized in Figure 6.
Discussion and conclusion
Primarily, these graph all result in the same conclusion, there is no fastest aerobar shape for every position.
Looking at solely the CFD results (figure 4) it is clearly visible that elbows extremely close to each other is faster with a monobar for both the high and low hand positions. On the other hand, spacing out the elbows gradually shows a diminishing advantage with the monobar till a crossover to where dual aerbars are faster. This goes for both arm angles, but with a different crossover point. If a conclusion had to be drawn just from the CFD simulations it would be: “Elbows close together? a monobar is faster. Are your arms spaced more spaced out? a dual bar will be faster”.
Adding the results of the wind tunnel test into the mix brings more of a nuance. As the individual yaw angle test results show (figure 6), dual bars beat the monobar consistently when the yaw angle increases. Combining all these individual results with the yaw weights (figure 6) shows that at a position where the elbows are completely touching, monobars still perform better over the whole yaw sweep. At the neutral position, dual extensions perform better over the whole yaw sweep. In between the best solution depends on the experienced yaw angle and thus on which events the athlete priotizes.
Implementation (Now what?)
We set out to find the fastest bar, or at least the fastest bar at each specific position. We did not achieve this, however we are 10 steps closer to this point and have been able to make a start on a decision scheme to figure out what aerobar shape we have to use for which athlete. At most widths used by agegroupers, we know dual bars are faster. If Ditlev reaches out to us (PLEASE) a monobar will be faster for him. For the big group in between we will talk with the athletes about their goals and priorities after receiving their measurements in our custom process.
I’d have loved to throw some super nice claims here, but in reality aerodynamics always comes down to the same 2 words. It Depends.
