Wind Tunnel Testing Ironman Pro Thomas Gerlach - Triathlon Aerodynamic Bike Drag

Testing @ A2 Windtunnel 
This past spring I spent $1,000 for 2 hours of wind tunnel time at the A2 Wind Tunnel
in Mooresville, NC. Although costly, I knew this was something I had to do to continue to improve as a professional triathlete. Unlike physical training, which focuses on building a bigger engine to go faster, this trip focused on making me more efficient by helping my cut thru the air like a knife.

While I had been familiar with the wind tunnel based on the reports of others, actually going to a wind tunnel gave me an entirely different perspective. This perspective will not only make future trips more efficient in my own planning, goals, and expectations, but it also gives me better insight to ask better questions of others. While aerodynamics seems like something of a dark art, it represents an opportunity for improvement for those that are willing to spend the time, money, and effort.

Given the complicated nature of aerodynamics I will be displaying numbers in two different formats. The geeks prefer to see results in CdA. I will also present the numbers in a simple 'watts' format. In this format, I will show the number of watts needed to go 26.0 mph. 26.0 mph is my typical Ironman 70.3 speed which equates to a 2:09:13 bike split.

For those people who are not experts at aerodynamics, please note the watts showed only include aerodynamic drag, it does not take into account the energy it takes to overcome rolling resistance nor does it take into account drivetrain losses. In addition, I tested at different wind angles referred as yaw. I don't want to get overly complex and discuss yaw. The important thing to know is that the real-world wind angles a rider experiences while cycling vary moment to moment. I chose to test at 0° and 10° degrees. This represents the majority of wind angles that I am going to experience in my races.

1. Baseline - the first thing I did was establish my baseline numbers. This represent the starting point which I hope to improve thru further refinement.

0°  = .246 .CdA
0°  = 238.1 Watts (Watts to go 26.0 mph)

10°  = .215 .CdA
10°  = 207.8 Watts

2. Position Changes - I then moved to making various position changes. I narrowed elbows, moved the saddle back and forth, the aero bar up and down. The data and pictures below represent the final position changes that I accepted. The changes were raising my front end up 1cm and along with narrowing my elbow pads by 2cm (1 cm each side) .

0°  = .240 .CdA
0° = 231.8 Watts

10°  = .211 .CdA
10°  = 203.6 Watts

3. Helmet Changes - I then moved to testing helmets. I had already been using a helmet that had proven to be fast on a high number of riders - that helmet was the LG P9 Helmet. I also tested a Kask Bambino, Catlike, Specialized S-Works TT, POC Cerebel, and Wasp Air. Often times some big changes can be found with helmets but for me the LG P9 was already the fastest. Pictures below show the second fastest helmet choice for me - the Kask Bambino.

Please note that I went to the tunnel before the Giro Aerohead MIPS came out. I now use the Aerohead MIPS and I did a short write-up on why that is here.

0°  = .240 .CdA
0°  = 231.8 Watts

10°  = .211 .CdA
10°  = 203.6 Watts

3. Race Kit Changes - I then moved to testing clothing. I started in a 2XU one-piece sleeveless kit that I raced in for years and was a size small. I also tested the 2XU sleeved kit that I had that was size small, a Cuore small sleeved suit, and a Cuore extra small sleeve suited. The Cuore extra small kit tested fastest and the results and pictures below reflect that.

0°  = .235 .CdA
0°  = 226.9 Watts

10°  = .207 .CdA
10°  = 200.4 Watts

4. Compression Sleeves
 - Given my large calves, I thought that adding some compression sleeves might help reduce drag. In the end, I had some 2XU MCS Compression Leg Sleeves (Amazon) (eBay) (Trisports). They were faster and the results and pictures reflect the change.

0°  = .232 .CdA
0°  = 224.3 Watts

10°  = .208 .CdA
10°  = 200.5 Watts

5. Shoe Change - One last change was shoes. I moved from some Pearl Izumi Octanes to Giro Empire SLX. The end results was the Giro Empire SLX were faster. The below reflects the final accepted change. For those interested, I did a full write-up of my Giro Empire SLX shoes with elastic laces.

0°  = .229 .CdA
0°  = 221.5 Watts

10°  = .200 .CdA
10°  = 192.8 Watts

Final Analysis - Looking at where I started and where I finished you can see that I made some considerable improvements in reducing aerodynamic drag despite already having the optimal helmet.

0° .246 => .229 .CdA
0° 238.1 => 221.5 Watts (16.6 watts decrease)

10°  .211 => .200 .CdA
10°  203.6 => 192.8 Watts (10.8 watts decrease)

What this means in the real world is that it would take less watts to go 26.0 mph. Or I could keep putting out the same watts and go even faster. Overall I was satisfied with my experience and certainly recommend the process for anyone that really cares about their race time.

Feel free to ask any questions you might have in the comments section below. Also, I will be writing a lot of good stuff in the next year. If you haven't followed me please do so. Links on the right side of the page include: Facebook, Twitter, Instagram, Youtube, RSS, and Google+. You can also follow the blog by email as well.

My Links:
- Spreadsheet with all data
- Post: Fastest Ironman Bike Shoes - Aerodynamics + Weight - Cycling
- Post: Giro Aerohead MIPS Triathlon Aero Helmet Review

Product Links
- 2XU Elite MCS Compression Sleeves (Amazon) (eBay) (Trisports)
- Giro Empire SLX Review (Amazon) (eBay)

Lastly if you are triathlete or endurance athlete, I am setting up a FREE Q&A group on Facebook. It will always be FREE. As a long-time age-grouper I spent way too long determining what information I could trust and what I couldn't. As a TRUE student of the sport I have learned a lot, remain open-minded, and realize that so many people disseminate information blindly and then myths become lore. Hoping to shed some light and simplify things for people.


  1. If we take Specialized's math at face value (-15w over 40km equals 80s saved), that's about 6.5 minutes off the bike leg. That's quite a bit, it it can be sustained.

    Did you find any heat issues with the compression sleeves?

    1. Well remember this watts stated are only at 26.0mph. Wind tunnel testing is done at 30mph assumptions usually. I haven[t done the math as frankly there is more to racing than just the maths and numbers. What is important is that it takes significantly less watts to go the same speed and that is good. As for compression sleeves, I never once felt even the slightest bit of heat from these. The Giro Aerohead MIPS, yeah at Cozumel 70.3 it felt a little toasty. Thanks for the questions!!! Happy riding :)

  2. Hey Thomas- Interesting results. I'm guessing you could get a *lot* lower than that with some work, though likely with some sacrifice to power. Also, just a comment that the watts numbers don't correspond very well to CdA at 26mph. I'm guessing your weight is about 150, so system weight is about 170. If I put CRR very low at 0.003 then assume zero transmission losses (so watts stated are at the hub not at the crank), I still have to put the air density down below 1.1 to get your watts numbers. In some ways it doesn't matter much as long as you are consistent, but I think more realistic parameters might be more useful for readers.

    1. Also, I had some other details in there that I took out. I was actually around 156lbs at the time, maybe a little more after the 8+ hour drive. I am sure that doesn't help with fluid pooling in the LegCannons as #BigRig Ray Bothelo calls them, going from the drive right into testing. It probably doesn't help with back flexibility either. Regardless, I am also 5 8.75 inches and have an inseam of 33.63 inches so lots of legs. As you can see from the data file, moving up actually helped, and the way I moved up was kind of sketch by simply adding more and more pads to the existing pads, which certainly has to add some drag. Many years ago John Cobb worked with me on a fit. He was very "anti-slam" with me. He actually wanted me upright, rockin' and rollin', generating all the power from hips/glutes etc. At the time I asked him what I could do, he said, "yoga" but it really wasn't any help in getting lower. Hence why in the last run, I actually tested a jank Mantis position. Despite the additional hardware it tested faster at 0. The data is in the file if you want to see.

  3. Thanks for the reply I did some quick input into CyclingPowerLab. I dropped the weight of the system to zero to take out RR and for .246 CdA it is giving ~243 watts versus my ~238. My roommate, who has a bachelors from Villanova in Math and a grad degree from Columbia in Mathematical Finance noticed something irregular in the spreadsheet, she tested as well, but at the time I wasn't really too interested as I was personally more interested in .CdA anyway. Shoot me message and let's talk about it. Just going off the file provided by A2.

  4. Thanks for the great post, Thomas. This does a nice job of countering the lower is always faster debate/obsession

    1. No problem Jim. I will add that there are a lot of people out there that understand aerodynamics but they don't understand triathlon, they don't understand swimming for 90 minutes to two hours and then getting on the bike and sitting there for 6-8 hours riding. They don't understand nutrition sitting in the stomach at a horizontal position. It is not to say it isn't the right approach for some. Too many people don't look at the whole picture, they don't look at the goals of the athlete and what is realistic - it is a huge disconnect.

  5. Awesome I know this will pay off down the road as well

  6. Love the blog. Since you talked about using compression sleeves, I had a quick question. What's the secret for putting on the sleeves in transition. I would think it would be incredibly tough since you're still wet.

    1. Joe thanks you for the kinds words and the question. I only wear compression sleeves when I can wear them for the swim. If I can't wear them for the swim, due to rules, then I don't wear them. It takes too long to put on something that is very tight.

  7. Replies
    1. Devon is only on temporary time-out. We are going to have to have a phone discussion though before the ban is lifted.

  8. Great insight into even the small changes. My God, though, I can only dream of being able to do a 2:09 at even your original 238 watts!

    CDA is a killer.

    1. That doesn't including rolling resistance or mechanical drag.

  9. So on avg what wattage output does it take for you to go 2:09 including rolling resistance and mechanical drag, for a avg course?

  10. At 5 feet 8 inches in depends on the course and the competition. Ultimately my competition dictates my pace in these races and watts are all over the board but usually in the 265-290 range.