The surprising link between running economy and range of motion, significant variation of rolling resistance between tire brands, and hard numbers around the use of latex innertubes. It’s flexibility, rubber, and latex. No kidding. Today, on Tri Talk.
Welcome to Tri Talk your podcast source for triathlon tips, training, news and more. To new listeners in Uruguay and Hawaii, I hope you are enjoying the ride. In Uruguay, I am impressed with the triathlon community that it established in that country. Keep us the great work. In Hawaii, I’m embarrassed to confess to you that up to the age of 30, I thought that pineapples grew on trees. Please forgive me. 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 64.
Today on Tri Talk its classic physics and physiology, the scientific comfort food of the triathlete. I’ll be covering some very interesting data regarding the specific costs of rolling resistance by tire brand and width. Some of the data is reassuring, and some of it is disturbing. Plus, is it worth dropping $10 on an innertube? We’ll find out with a look at the speed advantages of latex innertubes. Finally, flexibility is always good right? Right? It turns out that it depends on you goals as an athlete
In episode 63 we discussed the risks of going too hard on the swim, particularly in a sprint-distance event. One listener, William Jenks, pointed out an error on my part when I delivered that information. I frequently used the term “effort” instead of the term “velocity”. The researchers who tested the triathletes were very specific that they had the triathletes swim at 3 different velocities, not 3 different efforts. William reminded me that there is not a linear relationship between effort and velocity. When the researchers found that an 85% velocity was the best velocity for a sprint-distance event, that does not mean the athlete should aim for 85% effort, a term I misused in the podast. 85% velocity might only be 80% effort. Each triathlete needs to time their individual sprint-distance time trial, use that as a 100% velocity base-line, and then aim for 85% of that velocity, not 85% of that effort. Thanks, William for keeping me in check.
Also from episode 63 we looked at performance gains from swim apparel, specifically a speedo vs. a speed suit, with the speed suit coming out ahead by 19 seconds over 750 meters. Carl from Toronto asked if the study done considered any body hair on the athletes, as the speed suit would have covered that hair. Perhaps shaving the chest, back and thighs of an athlete would have the same 19-second advantage as covering that surface area with a speedsuit. Sadly, the study did not discuss how hairy the athletes were, only saying that the subjects were elite triatheltes, but it is a good point. Given the choice between shaving half of your body, or donning a speedsuit, I’d still pick the speedsuit.
Let’s get onto the good stuff! I came across a fascinating report from a site called biketechreview.com. If you have a chance, take some time to visit this site. This is not a commercial for these guys, I have no idea who they are, but I am impressed with what they have done. One of their forums users took the time to test the rolling resistance of dozens of tire brands. A reminder that rolling resistance, which sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a surface. It is caused by the deformation of the object, the deformation of the surface, or both. The simplest definition is that rolling resistance is the amount of energy required to overcome the friction between the road and tire.
A common misconception on rolling resistance is that to overcome it, you need to have 19mm wide tires and pump up the tire to the maximum PSI, thus reducing the contact patch between the road and the tire. When overcoming rolling resistance, the goal is for the tire to maintain a small but constant contact patch to the ground that can absorb the forces applied to it. Skinny tires with high PSI tend to lose contact frequently, and can’t absorb the forces placed on it as well as a wider tire with some give from a lower PSI. Of course, like anything else, more is not better, and this does not mean that a PSI of 90 is better than a PSI of 130. 120 is widely considered the optimal PSI to minimize rolling resistance.
Also, clincher tires almost universally have less rolling resistance than tubular tires. If you were to take a cross section of a tubular tire mounted on a wheel, you would essentially see a garden hose. If you were to take a cross section of a clincher on a wheel, you would see that the shape is more of a U, as the tire has to constrict at the rim to hook under the rim wheel. That U-shape in a clincher result in less rolling resistance that the perfectly round tubular. Does that mean that clinchers are superior to tubulars? Not necessarily, but I’ll cover that later on in the podcast.
What was most interesting to me from this rolling resistance report was the confirmation that not all tires are created equal. Some have the ability to maintain their shape much better, or have a stiffer sidewall, and the difference in rolling resistance is much more than I thought.
For example, the tire tested with the lowest rolling resistance was the FMB Silk Tubular, which is a bit surprising because it is a tubular, and I would have expected clincher. But, it was one of the only silk tires tested, and was also a very wide tire at 24mm wide. It’s rolling resistance coefficient was 0.00240. To give you an idea of what this means in terms of watts on the bike, if we were to take a trained cyclist, in a good aero position, 180 pounds total weight for bike, rider, fluids, the whole package on the bike, at sea level air density on a flat course, to maintain 24.6 miles per hour would take 340.4 watts.
Compare that to another popular triathlon tire, the Continental Competition tubular, 22mm wide. The rolling resistance coefficient on that tire is 0.00340, which for that same rider on the same wheel in the same aero position would take 349.3 watts to maintain that same 24.6 miles per hour. I find this very disturbing because this is the tire I race on my front wheel, and I race with a 19mm tire as opposed to the 22mm tested, which means the rolling resistance is probably even higher than that 0.00340.
But, I’m not totally depressed, because my back wheel has a Vittoria EVO Corsa tubular, with a rolling resistance of 0.00275, placing it at only 343 watts to maintain that 24.6 miles per hour, just 3 watts off the fastest tire tested. There is also another catch to this test which I’ll go over in a few minutes.
But 11 of the top 12 tires tested are not tubular, they are clincher. The clincher tested with the least rolling resistance was the Vittoria Ultra Speed, which unfortunately is no longer made by Vittoria. The next lowest rolling resistance, which is still easy to find is the Bontrager Race X Lite Pro, 23mm wide, with a rolling resistance coefficient of only 0.00244, requiring just 340.8 watts, or half a watt more than the top tire tested.
Another tire that was tested frequently, with different widths, that consistently came up on top was the Michelin Pro Light and Michelin Pro 2 Light. These tires at any width just dominated the low rolling resistance, with no tire having a resistance greater than 0.003. What is interesting is the Michelin Pro Race series was one of the worst across the board. Michelin makes both the Light series of tires and the Race series, and that Race series does not do well on these tests, but the Light series performs very well.
The Zipp clincher was another good choice, with a 0.00275 coefficient, requiring 343 watts. Overall, however, Michelin, Vittoria, and Bontrager at all widths dominated the top 20 in terms of rolling resistance.
But, there is more data to this that makes a huge difference. These tests were all done with latex tubes in the clinchers. 99% of all tubes that you’ll find in a bike store are the butyl tubes, not latex. In fact, the only makes of latex tubes I know if is Michelin, and at $10 a pop, it is heart-breaking to get a pinch flat when mounting them to your tire. There were some limited tests done with the same clincher tire, but comparing butyl and latex tubes.
Let’s look at that all-around good rolling resistance tire, the Michelin Pro 2 Light. With a latex tube, a rolling resistance of 0.0026, or 342.7 watts using that same rider at 24.6 miler per hour. If you were to switch to a standard Bontrager butyl tube, your rolling resistance goes from 0.00266 to 0.00322, 347.7 watts. A full 5 watts slower, which would equal about 9 seconds over a 40K time trial. At 2 butyl tubes at $10 a piece, that is a couple of dollars per second, not the biggest bang for your buck, but definitely a low-cost way to gain 5 watts of power. The report tested several other tires using butyl or latex, and the results were the same, about a 5 watt gain in power from using the latex tubes over the butyl.
Basically, any advantage that clinchers have over tubulars in terms of rolling resistance is wiped out unless you use the latex inner tubes. You can do a search on the internet for latext tubes and cycling, and you’ll find various on-line retailers who carry latex tubes. I wish I could say that PowerTri.com carries them, but they don’t yet. I can tell you that PowerTri.com does sell Vittoria tires, which were one of the best tires tested in this report.
Now, based on this information, should you go out and sell your tubular wheels and go back to clinchers? This data is telling us that we can put out 3-9 watts more if we use a clincher with a latext tube. Here is why I’m not switching:
Wheel weight. While a clincher tire might have lower rolling resistance over a tubular tire, a tubular wheel has a significant weight advantage over a clincher wheel. Since a tubular is glued on, it does not require that extra hook system the outside of a clincher rim requires. That extra rim material can add several hundred grams of weight to the wheel, and it is adding it to the worst part of the bike: the very outside of the wheels where the rotational inertia means that weight is more significant than anywhere else on the bike or rider. A 500 gram difference between two sets of wheels will cost a trained cyclists 20 seconds over 40K. Let’s make that more reasonable and say that a clincher wheelset is 250 grams heavier, and drop that down to 10 seconds. We know that 5 watts for our test cyclist was 9 seconds, and to me the benefit from low rolling resistance matched by the benefit from wheel weight. Plus, as soon as you hit the hills, rolling resistance won’t change, but your wheel weight will suddenly make a significant difference when climbing. That is why the tie-breaker to me goes to the tubular.
It is also interesting to consider the weight of the tires as well. For example, the Bontrager Race Light Tubular weighs in at 300 grams, compared to the Vittoria Triathlon EVO weighing in at only 190 grams. While both have similar rolling resistance ratings, That is 220 grams over both wheels, and that is a 10-second difference just between tubular wheels in terms of weight.
All tests were done at 120 PSI in an admirably controlled environment. You can read this report yourself by visiting the Tri Talk blog and clicking on the URL at the top episode 64, I’d read it to you on the podcast, but the URL is just too long. It is kind of interesting to look up and see if your tire is listed, and where it turns up on the list. This report was done by a gentleman named Al Morrison, and it must have taken and incredible amount of work. Al, wherever and whoever you are, you have done a great service to the triathlon community.
Two weeks ago Joe Friel presented a live e-clinic on how to pace for a steady state event such as a triathlon. If you missed that 1-hour presentation, don’t worry, we recorded it! Just go to TrainingBible.com and click on Camps and Clinics to find out how you can access this webinar. Also, while you are there, register for the upcoming live TrainingBible Coaching webinar on Aug 27th discussing the Paleo Diets for Athletes. Presented by Kelly Cawthorn, this live presentation will include a Q&A session at the end. This is your chance to learn from the expert how to apply Paleo Diet to your training plan and lifestyle.
Moving on. This next topic might ruffle a few feathers. Back in episode 36 I discussed two studies on the effects of flexibility. One concluded that flexibility was linked to decreased risk for injury, and another linked flexibility to increased strength and endurance. Those 3 reasons alone: injury prevention, strength and endurance, were enough to convince me to adopt a more aggressive flexibility routine. However, none of these studies actually linked flexibility to speed. Let’s take a look at a couple of other studies on flexibility and running economy.
The first study from the Int J Sports Med took 34 elite international distance runners and compared their running economy to the sit and reach test. This test will test the flexibility of the hamstrings and lower back. Each runner had their running economy tested at 16kph, or in other words how much of their VO2max were they using at that speed. A lower VO2max for the same given speed would mean better running economy.
The researchers found no relationship between running economy and weight, height, or age. Of course, since all 34 were elite international runners, it goes without saying that they had to all be young and lightweight. The only correlation that the researchers could find between these 34 runners and their running economy was their flexibility.
The runners with the worst sit and reach scores had the best running economy. The researchers concluded that, “stiffer musculotendinous structures reduce the aerobic demand of submaximal running by facilitating a greater elastic energy return during the shortening phase of the stretch-shortening cycle.”
OK, so maybe you are thinking that this only applies to elite runners. They are so fast that flexibility has no meaning at their level. Well, another study from the University of North Carolina took 19 well-trained but not elite 10k runners and assessed 9 measures of flexibility after a 10-minute warmup. They then performed 2 running economy sessions. Once again, even at the age-grouper level, there was no correlation between economy and flexibility. Again, of the 9 flexibility measurements, 2 of the 9 showed an inverse relationship. The less flexible the runners were in their dorsiflexion and hip rotation, the more economical they ran. These researchers also concluded that, “these results suggest that inflexibility in certain areas of the musculoskeletal system may enhance running economy in sub-elite male runners by increasing storage and return of elastic energy and minimizing the need for muscle-stabilizing activity.”
There was even a third study that was cited, but I could not find it. It claimed that 100 male and female subjects across a range of treadmill running speeds (0.9-3.13m per second), had a battery of 11 tests to assess trunk and lower limb flexibility. Analysis of the data revealed that subjects who exhibited tightness in the trunk (limiting turnout of the leg from the hip and trunk rotation) were the most economical at every test speed. Since I could not find the actual study or even the abstract for this, I’m not as confident as I am with the first two studies I discussed, but I still trust the source that cited it.
In summary, there is no study that I could find that links increased flexibility to increased speed or running economy. In fact, all the studies I found showed the opposite in terms of running economy. Now, one could argue that increased running economy does not necessarily mean increased speed. But this is a pretty weak argument to me. If someone can run at 16kph at 80% of their VO2max, vs someone running at that same speed at 85% of their VO2 max, all the first athlete has to do it go to 85% of their VO2max and they will pull ahead of the second runner. If running economy is not the holy grail of predicting run race performance, I don’t know what is.
However, I do believe that increased range of motion and flexibility is important in the following circumstances. First, in swimming, flexibility is critical. I don’t have anything yet to confirm this, but from what we know if the differences in swimming and running, I’m confident that this is the case. I do think that upper body stretching is important for swim performance. I don’t have an active upper body stretching routine, but after 10 years of putting on my own sunscreen on my back, I have managed to accidentally have great upper body flexibility.
Second, if you have a history of injury, or if avoiding injury is critical to you, continue with an aggressive stretching routine that targets those areas at risk. Missing 3-4 weeks of running from an injury does not seem worth any increase in running economy. But, if you have no history of injury, and you don’t stretch currently, maybe you are on the right track.
I recognize that at this moment, dozens of coaches are franticly loading their e-mail to write me. I hope this data is wrong, and that there is some data to backup flexibility and running economy. I just couldn’t find it.