Dr. Chester Kyle : Pioneer in Human Powered Vehicle Aerodynamics

Chester Kyle, PhD is a pioneer in cycling science and the aerodynamics of human powered locomotion. Now retired, he served as an adjunct professor of mechanical engineering at the U of California at Long Beach for several years. He also served a stint at Nike designing aerodynamic clothing. 

When you read the breadth and scope of his work, you really will be surprised how much of aerodynamic design and technology that has infiltrated cycling, whether real or gimmick, had been already explored by him and his students. From drivetrain efficiency to the aerodynamic drag of a shaved vs unshaved cadaver, there was practically little he didn't explore and write on.

Several ideas introduced by him and his peers at the US Olympic committee and human powered vehicle circles went onto win international cycling championships and setting speed records. At the height of his career, the UCI was hot on the chase of these "ideas", banning several of the improvements broguht to the UCI sanctioned cycling races. As Dr. Kyle likes to joke, 'the minute they saw them [plop], they became illegal'.

Dr. Kyle's investigations into technical aspects of cycling through simple experiments driven by a sense of economics and curiosity for the science should serve as an example for any investigator today. The most important aspect of these investigations was that he helped produce a body of empirical data that let other researchers and designers go about their business.

On 13th May 2010, he was invited to a seminar for the students of MAE297.  The following is the video from that lecture. An amazing little talk, and made no worse by Dr. Kyle's upbeat attitude and quirky sense of humor. 

Credits :
Film by the UC Davis Engineering distance learning program, 2010.

Perspective : Why is There No Indian in the Tour de France?

Such was a recent question on Quora.

There’s little reason to pick the Tour de France if you want to inspect the absence of Indians in international professional cycling. It’s what goes on at a more fundamental level of international racing that counts.

A quick example to analyze the parity (or lack of) in Indian performance with respect to other competitors in order to understand why it’s challenging to move up :-

At the 2017 Asian Road Racing Championships held in Bahrain, India did seem to have “decent” amount of pedal power in terms of two national time trial winners representing at the ITT and a total of six talented roadies at the TTT. Even though numbers weren’t on their side, certainly it was commendable that these six got an invitation to represent the country.

However, it panned out that the Kazakhs, South Koreans and Japanese would go on to cream the competition. The best placed Indian at the ITT was a distant 5th place from last in a total field of 18.

For a flat TT course, it is instructive to look at absolute power outputs as they tend to be an objective marker of sustainable intensity. The following power duration chart is from a Kazakh rider, who was among the winners of the men’s TTT that week.

You can see that 30 min power is pushing 500W. I’ll leave digging up the Indian power duration chart as an exercise for you.

These Indian pros could better describe the intensity of racing at this level to you. But personally, I see a gap of over 100 Watts for this duration between a Kazakh and an Indian, which is a,,,, little PACIFIC OCEAN to bridge in cycling parlance.

Performance in any sport is multi-factorial. Sympathisers will tend to say that national poverty plays a big factor in setting back the sport. On the other hand, if national poverty were the only deciding factor, you shouldn’t even be seeing a war torn country like Iraq or even for that matter, Mongolia or Uzbekistan showing up to the races, let alone place well in contention for podium spot at these races.

I’ll explore some other points that I think are important.

Facts of Life :

1) Physiological : As long as there is no raw talent, you will always be trying to fit a square peg in a round hole. At a fundamental level, performance in cycling is determined by a high VO2max and the maximum velocity and/or power output you can sustain AT steady state lactate level in your bloodstream. You take two cyclists - A and B. If B has a higher VO2 engine and can process work at a higher fraction of that for a longer period of time without fatigue, B is atleast on paper the faster cyclist at the end of the day. Unfortunately, sports science research and papers in Indian cycling are lacking in the public domain so we can’t make comparisons of national level Indian cyclists against similar international competitors. I do suspect there is a big gap in prime physiological indicators that define success in cycling.

2) Winning : One of ways to get into the TdF is through wild card teams. To be noticed for selection, you have to simply perform. You can have all the talent and train like a madman all year, but if you’re not winning and arguably by big margins, it’s going to be difficult. Essentially, the meat of a pro’s career is done and dusted by age 35 and the rest will be sobering to watch. It’s in the younger years that you can do some crazy things in life. For example, when ex US pro George Hincapie was still in his tender years, he was entering crits and lapping the entire field. Young Alberto Contador would show up at races with a heavy iron bike and still fry the field. The infamous Lance Armstrong competed in traithlons as a teenager and gave older experienced competitors a serious run for their money. Answering when can you see an Indian at the Tour de France is similar to how Africans entered the Tour de France in 2005, or for that matter, how Columbians entered the Tour de France in the 1980’s. Fundamentally, you need talent yes, but you need to win some BIG races on the cycling calender and you need the likes of Mr. Eddy Merckx and Mr. Bernard Hinault to notice you and bless your move forward. The Columbians had over 3 decades to mature as a cycling nation, today they have several top cyclists posted in the Tour de France.

3) Cultural : Cycling is a relatively new professional sport in India. In western countries, cycling talent is identified at a tender age and nurtured through the teens. People give a damn about it, they appreciate it. In India, families like to see their girls and boys get a good job, marry before 30 and get settled in life. Loitering the streets on a bicycle comes with a stigma. Furthermore, the collective culture of bike racing, when compared to other national pasttimes such as cricket, is dismal. On this point alone, we can write a big essay. On the other hand, one can argue that India is talented in sports like cricket, badminton, hockey and wrestling. TV air time and press coverage going to something India is good at, cannot be really argued against. There can be some balance, however.

4) Financial : There aren’t many bike races and professional development programs in the country. A few are springing up in parts of India, but nothing at the level to show normal average joe Indians that there is a professional future in cycling. If you can’t put food on the table and feed your family, I don’t care what it is - lorry driving, or gold merchandising, you won’t be doing it. In this respect, Indians are like any others from any other nation - they have their priorities.

5) Environmental : What we describe as the ‘quality’ of cycling, whether recreational or sport, depends in large part on the quality of the surroundings. Prime among them : clean air and good, safe roads. I observe that several Indians in inner cities defy the odds to enjoy cycling during weekends. However, the amount of particulate pollution (PM10, PM2.5) in cities like Delhi and Bangalore are ridiculous and exercising in these conditions would arguably shorten life span. Those who ride motored 2 wheelers on these roads are found to wear face masks to block pollution. Cyclists, on the other hand, are completely exposed and elevated breathing rates mean a lot of crap is going in. Something of a sea shift needs to happen in the traffic and emissions scene in India to provide an environment conducive to performance. This is a long term change that I don’t see happening any time soon. Even legislating that drivers are not allowed to use certain roads at certain times of the day comes with massive uproar. Until these changes come about, cyclists have to ride long miles to get out into the country from places of inhabitation. (The nice thing about India is that it is a democracy and if you make enough noise, people responsible for change will listen….or something like that. So use that vote!)

Positive Signs of Change :

The sport does seem to be exploding in India which is a positive sign. Bike shops and cycling themed cafes are springing up. Several cycling clubs attract people to buy bicycles and take up recreational riding and racing.

Another positive sign is a strong Indian presence in the management circles of the Asian Cycling Federation since Mr. Onkar Singh took office as it’s Secretary General.

A third is, as I mentioned, the growth of junior cycling development programs which is identifying talent and taking them abroad to countries like Belgium. One example is the Indian Pro Cycling Project.

One hopes these developments bring in :

1) A fresh pool of genetically talented Indians into the sport, whether that is nationally or from overseas residing Indians.

2) Support for Indian cycling at the international platform. Such is happening currently at Asian level as I already mentioned.

3) Provides Indians an exposure to international racing and a glimpse of the true demands of a professional career.

4) Encourages businesses to notice cycling and support talents with sponsorships.

5) Encourages talented sports scientists to study indian cyclists and publish findings in international journals. What are the physiological gaps and what training methodologies can best bridge them?

As a summation, I would argue that a string in essential supply chain needs to pop up to support the upward movement of Indian cycling professionals. Good bicycle manufacturers, mechanics, scientists, coaches, sport directors, sport management consultants, aerodynamicists, nutritionists, business people, sponsorships and importantly, partnerships with international facilities and people. The list goes on and on. In a challenging sport like cycling, you really have to sit on the shoulders of giants.

An Answer to India's Olympics Medal Drought

On the eve of Rio 2016, a BBC‬ writer managed to tie the words "Olympic", "losers" and "India" all in one headline. 

Cringe worthy? Indian papers say India has it's strongest contingent yet (this includes a 43 year old Leander Paes in the tennis squad!). Critics on the other hand argue ‪that ‎India‬ has a long culture of sublime laziness, kicking athleticism down in the priorities and engaging kids to be studious so they can be doctors or lawyers and a perhaps a better "value" proposition in an arranged marriage. 

Those things aside, in progressive cities like Bangalore, people are "discovering the sports" and a new means of ego-boosting. I doubt the next wave of Indian super-athletes will come from wide waisted middle managers riding expensive carbon fiber bicycles or aunties/uncles running marathons and brandishing their "also ran" medals. It keeps the spirit up but IMO there's little to show performance wise when they compete with athletes from Western countries. 

So what are the options? You can take the current crop of sportstars and keep hammering them to do better. However, there is no substitute to raw talent if you want to beat the best. 

Which is why I maintain this idyllic sense that it's in the cold high mountain states of North India or in poor and isolated foresty villages of Central and South India where people with statistically anomalous genetic potential reside. You would hope that in these parts of the country, teachers, sports coaches and sports governing bodies are keeping ears and eyes open to tap into this potential in a sustainable way, i.e giving new people an opportunity into sports without subjecting them to exploitation.

Ultimately, I think you can, with an outpouring of lots of money, organize fantastic training camps and bring up athletes over a long term to be world champions. But you can't organize training camps without first correctly identifying that golden potential by technically adept coaches.  Its a challenge but it's a big part of the answer to winning more ‪medals. Perhaps there ought to be a serious national hunt for athletes (and even coaches) in the same rigor as we search for beauty pageants, singers and dancers. 

In the following video, Indian coaches compare the Indian runner to the Kenyan runner by going over key physiological attributes required for maximum performance. It's an enlightening discussion on what's missing in Indian athletics by using running as an example.

Mechanical Cheating in Pro Cycling : An Analysis

The controversy of mechanical cheating in professional cycling is building up like an orchestra crescendo. Like the beginning of Lance Armstrong's infamous doping saga, reporters in Europe are mostly driving the exposé of this recent development. It sounded like a ridiculous claim to many until for the first time this year, a female Belgian rider was caught racing professionally with a motorized bike. Therefore, further attention to this issue is validated.

6 years ago when I explored a newsbreak by Rai TV's Davide Cassani on Cozy Beehive (see link), I looked into a power assist e-motor called 'Gruber Assist' just to find out the state of the art in pedaling assists. I estimated then that the 900 gram motor-control unit powered by a 1000 gram Li-Mn battery could supply a nominal 135 Watts for an hour from a 4.5 Ah capacity battery. There is a sleeker version of the Gruber Assist called 'Vivax Assist' which can reportedly supplement 110 Watts with a 6 Ah capacity battery. 

The motor’s maximum power can be calculated with a stall current and a nominal voltage and is about 50% of the stall torque for DC (see illustration on left). On assuming that Gruber's maximum short-term power was close to 200 Watts, it sounded like an appreciable supplemental power to use on a decisive cobbled climb. Such was the allegation from Cassani atleast.  

News broke a few days back that two French reporters, using infrared cameras, were able to track signals of "hidden devices" within certain bikes at the Strada Bianche and Coppi e Bartali races this year. No cyclists were officially named to the public. Five or more bikes were reportedly found emitting heat signals, with 5 of them at the seat tube and 2 at the rear hub and cassette.

At this point, the curious question might be : what is an estimated peak power necessary in cycling, for example, in an attack? Secondly, what are the required forces and crank torques? With those questions answered, one could begin an attempt to look for a motor. 

These questions was explored in a rough but fun estimation in a post titled Anatomy of a Cancellara Attack. As the title suggests, I was interested in plucking apart the physics behind a Cancellara attack using a video playback analysis technique. The focus was on a decisive segment in the 2010 Paris Roubaix when Cancellara attacked a pack of breakaway riders including another venerable specialist Tom Boonen. Cancellara would go on to win that race.

According to the estimations I made then, the speed transient in the attack went from 49 kph to around 58 kph (+/- 2 kph due to the error from the video analysis) in less than 5 seconds. The full results from the transient analysis based on estimations of Cancellara's racing weight, cadence and chosen gearing were as follows :

The 1190 Watts was reasonable for a Cancellara attack (infact just before this race, he had reportedly put 1400 Watts in an attack on the Muur at the 2010 Tour of Flanders). To drive this power at the estimated 100 rpm required an estimated 92 N.m of crank torque. 

Some years back, Andy Coggan Ph.D had shared plots from his "quadrant analysis" in which raw power meter data files were used to extract average effective pedaling force and circumferential pedaling velocity, which were then plotted on an x-y axis. Being a lover of all things technical in cycling, I quickly saved these for later reference and now they become useful.

The plots presented below show the signature of the preferred neuromuscular response of a rider to the stress of the riding scenario. Over several thousands of pedal strokes, a map is drawn out on the pedal force vs pedaling velocity chart specific to the racing scenario.

The first plot is from a flat 40k TT at an average power of 294 W at 80 rpm average. One finds variations are less and force is more or less concentrated around 200 N for majority of the time. Using 200 N yields a torque of 35 N.m using an assumed 175mm pedal crank. A high value of 550 N in the plot corresponds to a torque value of 96 N.m. This comes very close to the torque number from my own calculations into Cancellara's Paris Roubaix attack (see above). 

The second plot is from an actual road race on flat to rolling terrain at an average power of 250 W at at 78 rpm average. Here, unlike the sustained efforts of the TT, pedal force shows much more variations. 

In this plot, observe there were excursions in pedaling force upto 600 N and beyond. 600 N at 1.5 m/s pedal velocity using an assumed 175 mm crank length is still only 930 Watts at 105 Nm of crank torque. 

From the above discussion, one finds that crank torques in excess of 100 N.m are visible on a rider's pedaling signature, so the earlier estimate is not unreasonable. For the race winning attack at the 2010 Paris Roubaix from Cancellara, the first few seconds required 102-103 N.m at 110 RPM (assuming a 175mm crank length). 

Now what remains is to find a suitable motor able to deliver  approximately 100 N.m. My understanding of the precision motor market is limited, however there are very compact motors and planetary gearsets available. 

Below is a preliminary selection for a 4 pole x 200 W brushless DC motor. At 60-65 mm in length and just 30 mm in diameter, it's a tad smaller than an oversized road bike seat tube.  At a stall current of 171 A, it produces a maximum short term power of 171A x 36V = 6000 Watts, providing safety margins for cycling application. 

Since nominal motor torque is low, the motor has to be coupled with a precision ground gearset to be able to amplify torque at the low cadence of around 100 RPM. My previous experience in planetary gearsets have shown that "planetaries" offer low footprints with low noise generation. 

The preliminary gearset I could find was 80 mm in diameter. At 93:1 reduction in 3 stages at 70% efficiency, it can deliver a max continuous torque and power of 120 N.m and 410 Watts. Note that I had to go to the biggest gearset in this particular OEM's range to ensure the calculated torque estimate from earlier fell within the range of the device. At 81 mm, I suppose it could fit within the oversize 90 mm bottom bracket area but this needs checking.

Finally, a 90 degree 1:1 bevel gear is required on the gearbox output shaft to convert vertical downwards rotation to sideways rotation of the crank. A thorough investigation might yield a more optimal motor and gearing selection than shown below. 

What is interesting is that my preliminary selection totaled around 4 kg in weight, excluding weight of the battery pack and other required accessories.  A 45000 mAh powerbank I recently bought weighed 0.9 kg. So if we added another 1 kg, you're left with a total of 5 kg conservative that the cyclist has to carry. In a world where we have sub 7 kg carbon fiber bike frames, this exceeds 70% of that weight. I'm surprised that a commercial offering, if at all, could deliver attractive specifications within the weight and dimensional requirements of professional cycling.

That said, a custom built motor package specifically for someone intending to cheat makes sense. However, a package built in someone's garage could end up producing appreciable levels of heat due to low efficiency, unless the individual(s) making it knew what they were doing.

For example, a 200 W motor at 75% efficiency will produce, according to one chart online, 0.2 kW x 250 W/kW = 50 Watts heat loss which is 25% of the nameplate power rating. If this is the case, then using the given value of housing-air thermal resistance of 7.4 K/W and an assumed air temperature of 25 degree C, one expects the temperature of the motor itself to cross 300 degree C. Since the motor is constrained inside a sealed tube, that heat will build up within the space. Motor heat loss increases with efficiency drop.

Therefore, the claim that French reporters picked up heat with thermal detectors warrant a full fledged investigation.

Motor Selection (Example) 

Reduction Gear Selection (Example)

Heat vs Efficiency - Electric Motors

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Human Power at the Tour de France

To technically appreciate bicycle racing in the Tour de France is to fundamentally appreciate Newtonian physics, although purists will disagree to such bland reductionism. If you want to race up a steep mountain road, you need a net human power exceeding the retarding effects of tire rolling resistance and gravity.  When the road is a bit more nice and flat and where you tend to reach higher speeds, you need a net human power exceeding the retarding effects of aerodynamic drag. 

If you have large pockets, have your own bike fitted with a cycling power meter and inspect the wattage as you pedal. If you're savvier with numbers, fire up an MS Excel and program a little spreadsheet based on the math described in this paper by Martin et al titled "A Mathematical Model for Road Cycling Power". It should give you numbers that are unsurprisingly close enough to the reading from a power meter (exception to high windy days) because as mentioned earlier, cycling is Newtonian physics. 

The figure of merit for a Tour de France cyclist can be represented in terms of speed, absolute power, or power to weight ratio. Since the Tour is always decided in the mountains, being able to ride a bicycle uphill for long periods of time at somewhere between 10-15 mph (16-24 kph) is top class. During a sudden acceleration, a strategic move called an "attack" in cycling, being able to punch 18-20 mph (29-30 kph) for 10-20 seconds at a time is sheer top class. 

Power wise, being able to maintain between 330-350 watts for 20 or more minutes is great, somewhere around 380-400 watts or greater is top class. Power to weight ratio wise, a figure between 5.8-6.0 watts/kilogram is what it takes to deliver serious firepower in the mountains. Therefore, it doesn't assist you if you weigh 100 kilos rather than 70 kilos, because 70 x 6 = 420 watts is easier than 100 x 6 = 600 watts to do the same job.

The power to weight ratio allows for comparison between different riders. Since margins at the Tour is over minutes and seconds on a climb, a difference of 1 watt/kilogram between two riders makes the difference between sitting overall in top 10 or sitting overall in top 20 spot. In terms of money, that's worth something to a guy who earns his bread racing a bicycle. It's really as simple as that.

Riders often "warm up" on stationary bikes before the start of a stage, particularly before the start of a time trial, which is an individual race against the clock. They have a warm up routine, an instruction telling them how many minutes to spend at specific power levels.

Below is such a warmup sheet pasted on Alberto Contador's bike during a recent Tour de France. Alberto is a top tier professional cyclist and rides for Team Saxo Tinkoff. Inspect the numbers. He is asked to warm up at less than 150 watts, ramp up his output from there 30 watts each time all the way to 420 watts, followed by an easy spin at less than 150 watts. For an average individual, reaching 380-420 watts for extended periods of time can involve profuse sweating, high heart rates and dry-as-bone breathing.

A recent video posted online (see below) by hackers shows power and speed data of Chris Froome from Stage 15 of the 2013 Tour de France. On this particular day, Froome became the first British rider to win on the high mountain road to the summit of Mont Ventoux. Known as the "Giant of Provence", this road has a staggering average gradient of 7.6% for 21 kilometers. Froome would go on to win the 2013 Tour de France.

The Tour is especially interesting because of these dramatic incidences, where a community of rabid fans view extraordinary cycling performance and begin to have their own doubts about them. While there are people who can make careless mistakes with statistics, a simple understanding of physics and the records broken in the past Tours can tell any average Joe what might be possible in the realm of "ethical" sporting. I leave any judgment of Froome's performance aside and simply enjoy the action.