What a difference a wind screen can make, and the harsh reality of the legal draft. Back to my aerodynamic beginnings. Today, on Tri Talk. And…it’s good to be back.
Welcome to Tri Talk your podcast source for triathlon tips, training, news and more. To new listeners in the Czech Republic I want to thank you for your recent hospitality when visiting your great country last month, and that I worship your fellow countryman, Petr Vabrousek who finished 11 full Ironman events in 2008, coming in 3rd at Ironman Florida. My goal at Tri Talk is to help you swim, bike, and run faster, to meet your personal triathlon goals. Whether you are an elite or amateur triathlete, we cover sprint distance to Ironman distance. I’m your host, David Warden, and this is Tri Talk Episode 65.
I know it’s been a while since the last podcast, but I’m glad that you are back with me and ready for a consistent series of Tri Talk podcasts in 2009. You can count on at least monthly episodes, although they will likely be a bit shorter and less technical than previous publications. I’ve dusted off all the recording equipment and I think I can remember how all this stuff works. I’d feel al lot better if I could only figure out what this big sliver thing is in front of my face. Wait, I think it’s a microphone.
Today on Tri Talk I’ll be discussing a home-grown wind tunnel test I did over the summer. Most of that testing on bike setup and apparel simply reinforced what I had seen from previous wind tunnel tests, but there was one surprise in particular that I’d like to share with you. Plus, how much difference does the wave you start in an event make to your overall time? Let’s look at some simple math behind the legal draft.
Let’s get onto the good stuff! Last summer I decided to waste an entire morning doing some home-grown wind tunnel testing, and I think that some of the results are fascinating. I actually got the idea from a Tri Talk forums user who was experimenting with the same kind of thing. Now, before I start explaining how I did these tests, let me make it clear that this is was primarily for fun, for some easy podcast content, and I don’t hold these amateur tests as gospel at all. I can just see my good friend Professor Jenks of Iowa State University whipping out his calculator and practically fainting aver my lack of a controlled environment, sample size, margin of error, and statistical significance. This test was essentially me preaching to the choir, although I did try to make it as accurate as possible under the circumstances and I think you’ll find the effort was well worth it.
The testing took place on a long, low grade decent from a mountain road. I was able to start from a dead stop and slowly coast for about 75 seconds, reaching 25 miles per hour without ever peddling and holding 25 miles per hour for just less than the last minute of the run, until I hit the arbitrary end of the course, which happened to be a speed limit sign.
I would time a descent, sprint back up the mountain, change gear or apparel, and test again. To minimize environmental factors, I would terminate a test if I was ever passed by a car. Since the air temperature was rising as the sun came up, I alternated the tests back-2-back. For example, one descent with the Zipp wheels, the next decent with road wheels, the next with Zipp, and the next without for a total of at least 3 pairs of tests. If I did 3 tests in a row with Zipp wheels on, I was worried that by time I started the next 3 tests with road wheels the air temperature and pressure would be too different. I stayed on the white painted stripe on the side of the road to ensure that I maintained the same line as much as possible for each descent. I only drank fluid at the start of a new set of tests to make sure my weight was consistent for each set of tests. Even with all these measures, the test was riddled with flaws, but I got a real kick out of doing it.
After 3 test descents in a “baseline” position, I was really pleased that each run was within a fraction of a second of each other. I felt good about my ability to hit the stopwatch at the same point at the end of each run.
My first real test testing with and without the Profile Aero Drink up front. Again run #1 was with, run #2 without, run # 3 with etc. This was essentially revisiting John Cobb’s famous water bottle tests from earlier this decade.
I was a bit disappointed that although the descents without the Profile bottle were never faster than with the bottle, the biggest delta I ever got was 0.4 seconds faster with the aero bottle. Based on that 75 second descent, that would only represent at the most 19 seconds over a 40K ride at 25 miles per hour, which is a far cry from John Cobb’s 45 seconds he reported in his legitimate wind tunnel test.
I was disappointed but not surprised. The head tubes on modern tri bikes, like mine, are extremely short, much shorter than the bikes that John tested years ago. The ability for the Profile bottle to break up the air flow over the head tube cylinder is diminished when there is less head tube. The good news is that on my bike it didn’t make me any slower, and with the ability to get a drink without ever leaving the aero position, that bottle will stay on my bike for as long as I can see.
The second test was with aero helmet compared to a standard helmet. This test gave me the greatest benefit in understanding my setup, but I’m going to save the results of that test for the end of this section.
Third test was with Zipp up front compared to a Mavic Cosmic Elite up front. I did not ever swap out the back wheel because it was just too much of a hassle. Both wheels were at the same pressure, although the Zipp is tubular and the Mavic is clincher. There is certainly a difference in rolling resistance between these two tires, but the whole point was that I really wanted to see how if it was worth dropping $800 on a Zipp 404 up front instead of just sticking with my solid Mavic wheels.
The results at first were frustrating. The Zipp and Mavic had the exact same times, or at least the Zipp was not faster all 3 times, with the Mavis being faster once, and even when the Zipp was faster, it was never by more than 0.2 seconds. I was about to run my 4th pair of tests when what you have already probably figured out hit me. The Zipp 404 weighs 570g while my Mavic wheel is a whopping 850g, and that is before the tire where the Mavic wheel could easily add another 30 grams. Conservatively, the Mavic weighed more than 300 grams more than the Zipp, and since this was a downhill test, that extra rotational weight (rotational weight, not static weight) was pulling me down the mountain faster than the light Zipp. I came away feeling better about my $850 investment. It was so aerodynamic that I could add 300 grams to it and be just as fast as my old wheel.
The final test was swapping out apparel. I did the tests in either a Zoot Ultra tri tank and bottom, or a DeSoto one-piece LiftFoil. The Zoot stuff was nice and tight on my body, no flapping. To stay modest, I put the LiftFoil over the Zoot apparel, and then took it off for the Zoot runs.
I was thrilled to see that my little test mirrored the tests I saw from Colorado Premier Training, where they showed an 80 second difference over a 40K between apparel. Over my 75 second run, the one-piece was consistently more than a second faster than the two-piece, which would be at least 48 seconds for my test. To be fair, I was slightly heavier with the LiftFoil test because I was wearing two sets of clothes, but were talking a very small amount of static weight, as opposed a wheel’s rotational weight. This result is no commentary on Zoot or DeSoto. It is just the difference between a two piece with lots of pockets in the shorts and tank, and a one piece with no pockets at all.
Alright, let’s go back to my second test which I am saving for you for last. By the way, if you are thinking that I didn’t do that many tests groups, only 4, consider that I did a total of 38 descents (due to some cars passing me and having to cancel the run) at 75 seconds each, and that meant I did 38 ascents that took 150 seconds to get back up to the start of the run, plus time to swap gear and clothes in and out. I was there for over 3 hours, with 38 sprints up the mountain. I could barely pedal by the time I was done.
OK, the climax of the report was the helmets. I almost didn’t even do this one because I was so sure of the outcome. A standard Giro cycling helmet compared to a LG Rocket aero helmet. After doing the test 5 times, there was practically no difference, the biggest difference was 0.3 seconds once, and that was in favor of the regular helmet! What the heck was going on? The weight difference between the two helmets was almost non-existent, if anything the aero helmet weighed more and should skew the test in the aero helmets favor.
Now, I had removed the windscreen from the helmet for the test. On a whim I put it back on the helmet. The windscreen on an LG rocket is basically a plastic sheath over the eyes that molds very tightly to the helmet, like a built-in pair of sunglasses.
Doing the test 3 more times resulted in more than a second for each run with the aero helmet, or 48 seconds over a 40k. I was wearing regular sunglasses for all tests previously, but if you can picture an LG aero helmet, you know that the front of the helmet has somewhat of an protruding section, and this leaves the glasses pretty far back from the front of the helmet, whereas with the LG windscreen, it adds quite a bit of surface area flush with the front of the helmet. My theory is that without the windscreen, my facial area creates a pocket of dirty air, and somehow the windscreen keeps the flow even over the rest of the helmet.
In summary, these tests ultimately are more of a novelty than true science, but I they went a long way in boosting my confidence in the race setup of me and my athletes. Fvor those of you with an aero helmet, I would recommend the $20 investment in getting a wind screen, if they offer one. Also, the next time you go to buy a new set of clothing, you’ll generally pay the same price for a one-piece tri suit as you would for a high-quality top and bottom. You might was well get the one piece next time you buy some new clothes.
By the way, not only do you get free shipping at PowerTri.com for orders over $50, you also get a free Sprint or Olympic training plan written by me for orders over $99. This plan will guide you through 22 weeks of a Sprint or Olympic plan, for a beginner or an advanced athlete. If you are going to get some new gear for 2009, you might as well get free shipping and a free training plan from PowerTri.com . Who else is going to give you free shipping and a free training plan for spending $100? No one! I should know, I’ve looked.
Moving on! I’d like to begin this section on the legal draft by telling you a story.
Once upon a time there was an athlete named David. David lived his friend, the woman with the yellow hair. David was a good little triathlete, but, he was always curious.
David had another friend named Zane. In 2008, Zane beat David 3 out of 5 races. In each event, their swim and run times were very consistent. Zane consistently beat David on the swim portion, and David consistently had a faster time on the run. But their bike times were often different. David was curious. What could cause such consistency between the two athletes in 2 of the 3 sports, but such a difference on the bike?
Do I have your attention? Alright, let’s switch this story from 3rd person to first person. After talking to Zane after the last race of the year, he clued me in on something that should have been obvious to me at the time. In 3 of the 5 events where his bike time was faster, we were in different waves. In the two events we had the same bike time, we were in the same wave. Why would this make so much of a difference?
The first event we did was a duathlon where the cycling was done and then the entire bike portion. The race directors allowed the cyclists to start whenever they wanted, and their chip time simply began when they crossed the mat. I was so excited I was the first one out the gate and led from end to end, only to find out when all the times had been calculated, that I have actually come in third. Two people who had started behind me had a net faster time. Unlike me, Zane had waited 10 minutes after the first cyclist had left, and almost all the field was on the course before he began his chip time.
Why would he do this? Because by starting out behind several dozen or a even a few hundred cyclists, he was able to get a legal draft on each one he passed.
Let me give an even more extreme example. In the final event of 2008, Zane creamed me on the bike, and I was outraged because I had hung with him on so many other events. In this wave start triathlon, I had registered in the Elite division, where only about 30 left in the first wave. I came out of the water in 9th, and passed just 4 people on the bike without being passed.
Zane, however, went age group instead of Elite and was in the 4th wave. This was an 1,800 athlete event, and by the time he got to the bike, there were 1,000 people already ahead of him. However, 600 of them had already gotten to the run by the time he finished his ride, and so he passed only 400 people during that 40K ride.
What would it do to a bike ride if Zane was able to pass 400 people? Let’s assume that for the 15 seconds you are legally passing another cyclist in a triathlon, you realize a 20% reduction in drag. Since drag is 90% of the resistance on the bike at speeds over 20mph, let’s conservatively say that he would be just 15% faster for the same effort for those 15 seconds. In fact, let’s just give him 10 seconds that he was in a legal draft zone instead of 15 to pass a cyclist because he is a fast rider. Again, I passed 4 cyclists, he passed 400.
Even though he passed 400 people during his ride, I’m not going to assume that all 400 were lined up nicely for him one-by-one. Realistically, he probably passed a total of 100 groups of cyclists.
So let’s do the math. 15% faster for 10 seconds times 100 cyclists means he was going 15% faster for 16 minutes of his 1 hour ride, which equals over 2 minutes. Heck let’s just say it was only 50 groups of cyclists. That is still over a minute saved in legal drafting. I advertised this as the harsh reality at the top of the show, and that reality is, for every cyclist you pass legally, you will likely shave about 1 second from your ride time.
Before you become outraged at my suggesting you take advantage of a legal draft, consider this as well. What if you are passed by 400 cyclists? You have very little control over this. Would not the benefit be the same? The draft zone you gave him will be there for just as long for you as he pulls ahead of you. In fact, one could argue that the benefit in being passed is greater than the benefit in passing, because it will take a longer amount of time for the passing cycling to get a lead of 3 bike lengths, than it took him to close the gap of 3 bike lengths when he began his pass. Essentially, for those 20 seconds, the two of you have become a team in a little peloton together, both taking advantage of a legal draft.
You simply can’t help being a beneficiary of a legal draft if you ever pass or get passed. It is simply a legal and necessary part of the sport if you complete the pass within the allotted time.
The legal draft is like commodities trading. It thrives on volatility, whether going up or down, you make money. Whether being passed or passing, you get some benefit. Like me passing just 4 cyclists over 40K, there was no volatility. But passing or being passed by 50 or more cyclists over 40K can make a big difference.
But can really use this information and create a strategy around how to race so that you will either pass a whole bunch of people or be passed? The only practical method I can think of is exactly what Zane did. If you are an above average cyclist, whenever you have the chance to start behind a large number of athlete, such as age group vs Elite, it might give you a real benefit to do so.
Episode 66 will be a two part series, with the first part out in just another week. This episode is a fascinating and lengthy look at the USAT ranking systems, with a review of the ranking systems of 3 other major triathlon federations. This information is one the most exciting episodes, at least for me, that I have ever done. If you are a member of USAT, don’t miss this episode.
I’d like to do a quick shout out to my athletes. Congratulations to Darren and John for their courageous finish at their first Ironman in November. This episode is dedicated to you, John. I’m going to miss you this year, Darren. To Kim who worked her hiney off in 2008 and qualified for the World Championships in Australia. And to Jeremy and Michael I am looking forward to working with both of you in 2008.