AeroLab Tech

Freeride analysis is now live in a beta distribution! This tool is to help coaches, fitters, and athletes understand how CdA can vary when training and in race like efforts! It also offers an excuse to get out on days like these! 😉

After a long winter the sweetest days are field days. Big developments on the horizon! Stayed tuned 😉

A great few days at the riding, racing, product testing, and spreading the love of aero!
R&D engineer competed in the B category of the circuit and road race with the primary take away of how fast the Californians are!
A few key take always from Matt’s tactics and analysis related to the importance of positioning and aerodynamics soon to follow!

How important is aerodynamic adaptation?

Above is a graph following the story of an athlete improving their aerodynamics and adapting over time. The blue curve shows the power to overcome aerodynamic drag while the yellow curve show steady state speed accounting for all losses. This athlete was able to increase their TT speed with no change in FTP (270W) or hours on the bike.

A recently tested athlete told us the story of how they got aero over the past two years. The first improvement was clip-on aerobars with their road bike (point A, CdA 0.295). Being well back of the leaders they were motivated to purchase a TT bike and adopted the “slam the stem” mantra. Needless to say, in their next race they blew up attempting to hold target power 270 Watts in a new “aero” position (point B, CdA 0.277). Their race performance hadn’t improved by simply purchasing a new TT bike.

Stumped, our athlete decided to visit a aero-certified bike fitter. Following an in-studio bike fit and trying on a TT helmet the athlete tested on the road at a CdA of 0.251 (point C). Optimizing helmet choice over a series of tests the athlete was able to drop further to a CdA of 0.244 (point D). The fitter explained to the athlete that achieving this position would result in a decrease in sustainable power without adaptation, notice the drop of about 15 Watts.

Consistent training over a 4 month period in this new position the athlete was able to bring up their target power from 255 back to 270. In addition, trying a aero-road helmet which better conditioned the air flow over the rider, the athlete was able to further decrease their CdA to 0.233 (point F). This reduction in CdA from point D to F is not solely due to the change in helmet. Due to the adaptation over the 4 month period the athlete was able to comfortably maintain position. The only change to the athletes daily routine was more training in aero.

From the CdA values we predicted the athletes 40km TT performance on a flat smooth course for positions A and F from 61 min and 22 sec to 56 min and 39 sec, a decrease 7.74%.

Wait? Isn’t drafting illegal?
In the Figure above we have plotted how much power you can save while riding ‘in the draft’ of a lead rider for various wind yaw angles. The vertical red lines show the legal limits for bike spacing within World Triathlon and Challenge events. You may wonder “why does wind yaw matter?”: Although crosswinds cause portions of the first rider’s wake to be redirected off-course (reducing draft effects), even at modest yaw angles it is possible to benefit from ‘drafting’. In the plot below at a 12 meter `drafting` distance and moderate wind conditions a rider can experience a reduction of 10 to 40 Watts (5 to 18%) to maintain the lead rider’s speed (44 kph in this example). In contrast, at a 20 meter distance the reduction is less but still significant at up to 15 Watts.
So what does this mean for you? If you can swim like a fish just hold a second while we catch up. For the rest of us, it is possible that burning a few matches on the swim to stay with a strong group can pay dividends in power savings on the bike even at legal ‘drafting’ distances 😉

Is this a simulation or is this something more?
Understanding cycling aerodynamics is at its core understanding how a rider influences his or her pressure field and intern how this pressure field produces forces on the rider i.e. drag (CdA). Wind speed and mechanical pressure are at ends with each other; neither can exist without the other and every where the wind goes pressure got there first. Below is a glimpse under the veil of how AeroLab’s cloud processing can account for these effects to accurately measure a riders CdA from three simple pressure measurements.
In brief, when a cyclist rides through the air they will experiences a relative wind vector, for example, a slight cross wind at 40kph. Slicing through the wind they affect the local pressure all around them resulting in the drag force slowing them down. Applying our data driven algorithms we are able to account for how the pressure field is modified by the cyclist. This allows us to determine with great accuracy the wind yaw, wind magnitude, and even detect disturbances like passing cars or other drafting cyclists. All of which is data driven and based on three tiny ports on the sensor itself and we think that’s pretty cool

This week we wanted to talk about something all cyclists and triathletes think about, weight. As most athletes are now heading into the off-season it’s time to look forward to holiday dinners and the occasional extra beer! It’s normal, if not beneficial, for an athlete to put on a little extra weight as we wind down our training volume in preparation for the next cycle! We wanted to put it in perspective how adding up to 2kg compares to any equivalent decrease in the magnitude of CdA.
Using the same example rider from our previous post we assumed an input power of 250 watts to calculate our steady state speeds. In the first slide we have iso-contours of the additional power required to maintain speed for the added mass (y-axis) vs road gradient (x-axis) if CdA is constant. In the second slide we the same figure except solved for for the amount needed to decrease CdA in order to maintain the same speed.
The most important difference between the two figures is the shaped of the contour lines and how quickly the colour changes. What we mean by this is in the power map (slide 1) it is clear that an athlete would have to increase their power as the grade increase with additional weight, news to no one. However, in the CdA map (slide 2) there is much more blue and a more gradual change in the required CdA decrease. This shows that even modest improvements in CdA can account for fluctuations in weight as until the road is very steep.
All in all, we wanted to show the relative importance of weight and CdA and how even up to 2kg is only a 6 watt increase! As long as we don’t go crazy in the off-season that weight will come off come race day and any improvement in CdA will just be gravy 😉

How much slower is it to sit up during a time trial?

We’ve all heard from our “fast friend” that sitting up on climbs and focusing on power is faster than trying to hold position when the road tips upward. Here at AeroLab we wanted to shine some light on this statement by offering a sample calculation 🤓

To start off we assumed our test athlete is able to hold a target power of 250 watts over the duration of their event. This rider plus bike and kit weighs in at 83kg with a CdA of 0.225 when in aero and 0.350 when sitting up but not standing.

Assuming a drivetrain efficiency of 98% the power input to the system is 245 watts propelling our rider forward. How this energy is distributed into aerodynamic drag, rolling resistance, and potential energy as the road gradient increases is shown in slide 1. We can see at roughly 1.5% the contribution of aero and potential energy is equal at about 110 watts with the potential energy increasing as the road gets steeper telling us what we already know; going uphill is hard!

In slide 2 we have a comparison of the total power required to go the same speed in aero (blue) and out of aero position (orange) as the road gradient increases. To do this we assumed our rider was in aero the entire ride, solved for the steady state speed, and increased the CdA and solved for the power required. As you can see even up to a 3% grade there is still an advantage of holding position of roughly 30 watts! As expected this difference shrink as we approach a 6% grade but the road has to get a lot steeper before holding position becomes unimportant! This would be even more power if the rider was standing with CdA values exceeding 0.4!

So what does this all mean? In slide 3 we took the half of Ironman Mont Tremblant course and calculated the rider’s speed in and out of position at each road slope and added up the lost time. If out of position whenever the gradient is more than 1.5% it would taking an extra 5 minutes and 6 seconds or our rider would have to hold an extra 30 watts over the entire 90km course, showing once again that

Ever wonder how aero is aero; how you stack up in terms of both W/kg and aerodynamics; or how much faster you can be through improvements in either power or position? Using our database of outdoor aerodynamic tests we were able to put together some basic graphs and charts to answer these questions.
In slide 1 we have a distribution of rider CdA values while in the TT position. These values range from 0.337 to 0.164, but this isn’t the whole story. This graph describes how riders compare from an aerodynamic point of view but not how fast they will go.
Dividing the rider’s W/kg by certain CdA percentiles (from 5 to 95%) we are able to produce a performance ratio (slide 2) that captures how strong a rider is but also how limited they are due to aerodynamics. For example, if you are a Cat 1 in the 68th aero-percentile capable of producing 4.88 W/kg your performance ratio is 22.03. This very close to a world-tour pro pushing 6.03 W/kg in the 50th aero-percentile!
Now for the good stuff. In slide 3 we are able to take this performance ratio and solve for the rider’s average speed on a flat course assuming a weight of 75kg. We can see now that our Cat 1 rider is able to hold 48 kph while the pro is at 49.8 kph.
So how do we use this information? Say you are able to produce 3.5 W/kg for the duration of your event but you keep coming up short averaging just under 40 kph while the winners in your category are closer to 42 kph. You know the potential at your W/kg is close to 45 kph meaning there are lots of aerodynamic gains to be made!

This early Apollo road bike is a snapshot into the state of the art in cycling aerodynamics back in the 1980s. Equipped with Dura-Ace AX Series aerodynamic bicycle components this is a true work of art and engineering; from airfoil frame tubing to aero optimized water bottle, brake callipers, wheel hubs, and even pedals. The industry has come a long way but we still like to look back and appreciate the early innovators!