Making the most of your cycling power…
You put in the time with focused intervals and long endurance riding to build your “engine”… but how do you turn that into speed on the bike?
Shorter Summary:
Aerodynamics is the largest consumer of your cycling power, on average.
Aerodynamics isn’t something that you can eyeball as to what will “make you faster”. While we absolutely support and recommend the use of good bike fits for comfort and limiting injury potential, going to a fitter to put you in a “faster position”, doesn’t mean you will actually be faster… unless they have a method of quantifying the changes made. Likewise, automatically assuming that making your body lower or choosing X wheelset because some tests showed it was faster than brand Y may not be true for you.
Tri2Max offers two aerodynamic testing systems in central Iowa to evaluate your cycling aerodynamics:
4iiii/Stac Virtual Wind Tunnel. This method utilizes a complete 3D scan of you on your bike, utilizing Computational Fluid Dynamics to simulate wind tunnel performance and can provide comparisons of body position changes or gear alternatives and the impact on your speed or power. *** Note, 4iiii’s/Stac has temporarily halted this service due to personnel changes, but plans to offer it again later in 2022 ***
Field Testing. This is a comprehensive testing process that you perform on your bike, with your gear, to evaluate the impact of position or gear changes. Although more time and expense, this methodology will translate the most directly to real-world race performance. Tri2Max utilizes aerometers (field testing devices, measuring wind speed, ground speed, slope, temperature, atmospheric pressure, etc.) to estimate CdA and relative changes in gear or position.
Aero testing isn’t just for time-trial specialists or triathletes… it can be an important factor for ultra-cycling as well as gravel. Why? Long duration events typically mean athletes are riding with less power, so riding efficiently becomes extremely important… with no watts wasted. Tri2Max has evaluated unusual gear for aerodynamic testing (front roll bags or large rear bags) for multi-day self-supported events as well as body position changes (aerobars vs drops) for gravel, utilizing the VWT as both a cost and time-effective way of comparing alternatives.
If you are interested in aerodynamic testing, please contact Greg Grandgeorge at ggrandgeorge@tri2max.com.
Detailed Discussion:
Big watts may be great for bragging rights, but it doesn’t inherently get you to the finish line faster. At the end of the day, you need to turn that power (and associated work) into speed on the bike. There are certainly a lot of considerations, but aerodynamic losses are generally the most significant consumer of your cycling power. The key thing to understand is that the relationship between speed and aerodymics is not linear… aero losses increase by velocity cubed.
You can try this cycling power calculator directly at: https://www.gribble.org/cycling/power_v_speed.html
What impacts aerodynamics? Body position, bike frame, wheels, helmets, tire width, tool/food bags, water bottle position and even the clothing you wear. The challenge is that aerodynamics is very individualized… what may test as the fastest helmet on a mannequin may be a poor choice for you as an individual. Likewise, raising your aerobar hand positions may work well for a specific pro triathlete, but may turn out to be slower for you, based on the rest of your body position.
How can you quantify what will make you faster specifically? Cervelo has a great white paper on what they use for design, and it’s a combination of Computational Fluid Dynamics (CFD), Wind Tunnel Testing, and Real-World Testing, which would be relatively common for most major cycling manufacturers. The deep dive paper is located here. What about athletes… what are the options if we want to test positions or gear?
Wind Tunnel. Typically, this is what is used to test gear (bikes, helmets, wheels, etc.) as well as test athletes as well. Historically, this was seen as the gold standard for testing athletes, in terms of accuracy and repeatability. Although a great way to test overall, the practical challenges with wind tunnels are threefold:
Wind tunnels aren’t located in every city, so for most this means traveling with your bike to get access.
They can be expensive… $900 or more to be tested in the wind tunnel, not including travel costs.
The results are valid for idealized conditions. There aren’t wind gusts, riders are typically in their best position when tested, and the rider, wheels, etc. may not be moving (and certainly not moving relative to the ground) as we’d see in real life.
Computational Fluid Dynamics (CFD) Analysis. In a simplified sense, this is using computer modeling to simulate what happens with aerodynamic drag in a wind tunnel. CFD has been used for years in many industries and is used by most major bicycle frame and component manufacturers. More recently, CFD has been extended from just testing components to testing 3D scanned athletes on their bicycle, using 4iiii’s Virtual Wind Tunnel (VWT). The Pros & Cons of CFD are:
Better potential availability. Using a portable 3D scanner, a scan be performed in virtually any location, by a qualified VWT partner… minimal travel required.
Much more cost-effective. Typically, scans and the associated report are comparable to the cost of a bike fit. Tri2Max does scans in the Des Moines area for $250 per report and offers a discounted rate for T2M athletes ($175) and some participating cycling or triathlon clubs / teams ($200). This is around the cost of a bike fit, and is substantially less than the cost of new carbon wheels… and the wheels may not provide the benefits you had “hoped” they would. VWT can run simulations with slightly different body positions (e.g. stack height, elbow width, hand positions, head positions, shoulder shrugs, etc.) as well as different gear (different helmets, wheels, bottle positions, etc.). Each report contains 5 different alternatives (baseline plus 4 changes). Note that completely different body positions (e.g. aerobars vs hoods) or a different bike, would require a second body scan, and would be a separate report.
Like a wind tunnel, the results are valid for idealized conditions. The VWT is generally within 2% of a wind tunnel result, which means it also is for consistent airflow, and without moving conditions, similar to a wind tunnel. That said, both the wind tunnels and CFD can provide good relative differences in gear or position (e.g. this change will save you X watts or increase speed by Y). For those interested in more, episode 35 from Flow Cycling talks to VWT founder Andrew Buckrell.
For an example of a real VWT report performed by Tri2Max, see the following VWT Test Report link. Note that the positions evaluated are shown on page 3, baseline, elbows 30mm closer, elbows 30mm closer plus 20mm stack height, baseline shrug, and baseline shrug with high aerobar hands. In this example, the savings from baseline to the final position (shrug with high hands) was around 47 seconds on a 40k TT… with no changes in gear.
Real-World Testing. There are tools like roll-down testing, Golden Cheetah’s Chung Analysis, and Best Bike Split that can be used to estimate gear differences. The great news is these can be performed by most people themselves, with their own equipment. The challenge is the variation in outdoor testing (wind gusts, etc.) can create issues with repeatability and make accuracy questionable. In the past few years, Garmin (and others) have invested in technology to do aerodynamic testing inside indoor velodromes. Often they utilize power meters and on-bike sensors to estimate aerodynamic losses, similar to what you see in a wind tunnel. More recently, several companies have created packaged sensors that can be used outdoors, to measure speed, power (via a standard power meter), slope, vibration, and wind speed), to also estimate aero losses on the bike.
The pros and cons for field testings are:
Availability will be a function of distribution in the marketplace, but the cost of entry is much lower than wind tunnels, so likely this technology will become easier to access with time. Great availability for areas with a certified coach/fitter, as it’s not dependent on the use of a tunnel or velodrome… it can be done on any quiet, relatively flat, low-traffic roadway.
Cost is moderate, compared to CFD or Wind Tunnels. Typically, the Garmin aero testing in a velodrome is around $600 per session, not including the costs for velodrome usage. The cost is $400, which includes around 2 hours of testing time, to test multiple positions, gear, bikes… whatever you choose during that time. Practically, this may be about 4-6 alternatives, depending on how much time it takes to change positions, gear, etc. Discounts are available Tri2Max athletes ($275) as some participating triathlon clubs/teams $350 (TriRacers of Iowa, some local bike clubs, etc.). On a limited basis, Tri2Max will have an option available for remote T2M athletes to have an aerosensor shipped to them, along with a Garmin, to perform their own field-testing (with Tri2Max assisting with instruction, analysis, and generating a report of the results… contact Greg if you have an interest in performing your own field-testing).
In general, during field-testing sessions comparing predicted values to the Virtual Wind Tunnel, we’ve observed consistent differences between the two methods relative to gear changes and positions. General observations of when which method may make more sense:
VWT is likely better for very small changes (e.g. how much drag is there when I add a pump next to my water bottle on the downtube). Practically, small changes can be lost in noise during field-testing (e.g. small changes in head position while riding can impact the results more than adding a small pump).
VWT is simple and cost-effective to make changes and see relative differences for gear you do not own, or to make simple position changes. For example, if you’ve already been scanned and want to see the impact of different types of aero helmets that you don’t own, you can “try” (they can model) how different helmets (that they have models of already) will impact your CdA. Likewise, if you want to try different water bottle configurations, it’s easy for them to move them behind the seat, between the arms, etc. Some position changes are relatively easy, such as changing stack height or changing forearm position. Large changes, such aero position versus hoods, requires a separate scan.
Field-testing is better for comparing different cycling kits/clothing. VWT isn’t able to model material differences, and it makes assumptions about what you are wearing and how it impacts aerodynamics. Specialized has shown some pretty large differences in clothing in the wind tunnel, and field-testing provides a great opportunity to see the impact of your own specific kits and how they help or impair your aerodynamics.
Field-testing is likely slightly better for testing gear that you own or for finding nuances in positions, based on the normal head position you hold when riding. During a scan, you are in a static position. This may be an ideal position that you can’t really hold when dynamically riding (same is true in a wind tunnel). During field-testing, we often see slight changes in position as the ride continues (usually shakes out during the initial test period)… moving more toward what you actually hold during normal riding. This provides the opportunity to get more realistic comparisons between alternatives.