Dot Physics

Do Bikers Cheat?

Well, maybe that isn’t the best title. You see, there is this video going around saying that it is possible that a professional bike racer was cheating by putting a hidden motor in his bike. I am not really going to talk about the cheating aspect (my gut feeling says that it would be too easy to catch, so he is not cheating).

Actually, there was an interesting analysis by Ron at CozyBeeHive. Quite a thorough job. He even used Tracker Video Analysis. However, he didn’t use some of the nicer features of Tracker, so I figured I would do this analysis also. Plus, you know I love bikes.

Although I like bikes, I don’t know too much about professional cycling. I am just going to trust Ron about which guy to look at. Here is the whole video that he takes the clip to analyze from.

Video Analysis

There are a couple of things that Ron missed with his use of Video Tracker. First, calibration point pairs are awesome. Basically, you can just take a couple of points in the background and find how the background moves. Then when you mark your objects, it will give you their motion. Here is an example I did with calibration point pairs.

The other thing is that you can actually do linear fits (and more) in Tracker itself. No need to export to Excel.

There are a couple of problems I had with Tracker though. First, I couldn’t see how to show a graph with two different objects. I am sure this can be done though. My second problem was that this track was quite long. For some reason, I couldn’t keep making an infinite number of calibration points. Ok, well, I just broke the motion into two parts. Here is the first part with the guy in question (Fabian Cancellara).

i-422545f21c252c0edf335afcbf7da5f3-2010-06-07_data_tool_11.jpg

So, during this first part, Fabian has a speed of about 13 m/s (about 29 mph)

What about his acceleration during the first part? I could make a plot of velocity, but it would be easier just to fit a quadratic function to the data. Here is a description of finding the acceleration from position data, in case you are curious. Here is the same data with a different fit.

i-32f8ed71926251b562fd4d68161b744f-2010-06-07_data_tool_12.jpg

During this part, Fabian has an acceleration of 0.698 m/s2, or if you like it could be 1.56 mph/s. Also, for comparison, I plotted the speed of the lead biker guy. Here is his position with a linear function fit to the data.

i-59f11f3f3f906dbf1b684a8cc971a605-2010-06-08_data_tool.jpg

From the fit, he is going about 10.8 m/s (or 24.2 mph). What about the second part of the motion? The two bikers (or should I say cyclists) have about the same speed as they did during the first part.

How does this compare to the values that are posted at cozybeehive? He got a value of around 25ish mph. So, in the same ball park.

Maybe the real question should be how does the speed of Fabian compare to the pack? I still could not figure out how to show both riders positions on the same graph in Tracker. So, I exported that data to Logger Pro. I also fit both a linear and a quadratic function to both sets of data. Here is what it looks like.

i-9657fed18e8a287a4840c90d4cd2e9d1-2010-06-08_untitled.jpg

Both riders are accelerating just a little, but Fabian is going faster (with a greater acceleration also). I am not going to (yet) go into a power discussion like Ron did, but I will just say that neither of these biker motions seems too crazy.

Bonus

This is how awesome Tracker Video can handle stuff (even if I didn’t do the best calibration job).

Comments

  1. #1 dean
    June 8, 2010

    The bike weighs less than 16 pounds (possibly, if not probably, closer to 14) – every gram of weight is agonized over. How light could the engine be, and would it provide enough oooomph at the critical time to justify carrying the damn thing for the rest of the race? I don’t buy it (the bike, @ about $10000, or the assertion)

  2. #2 Eric Lund
    June 8, 2010

    I agree with Dean. The Beehive link quotes a mass of 7 kg (roughly 15 pounds) for the bike and 80 kg for Mr. Cancellara. I would assume, as Dean does, that 7 kg is about as light as you can make the bike and still have it do everything a competitive racer needs to do. If Cancellara has a clandestine motor in that bike, he also has to have a battery pack and a control system (TdF stages are typically several hours long, so using a motor for the entire distance is obviously impractical), and the whole thing has to weigh not very much. That last part is the tricky part.

  3. #3 Rhett Allain
    June 8, 2010

    @Dean and @Eric,

    That is really a great point. You couldn’t use the motor the whole time, so it would probably not help.

    Also, I just don’t see how he could hide this (sound of the motor included).

  4. #4 Emory Kimbrough
    June 8, 2010

    So, riders juiced on steroids and bikes juiced on solenoids…

    This story received enough attention that it recently made it to the New York Times “Most E-mailed Articles” list. Here’s the Times article:

    http://www.nytimes.com/2010/06/05/sports/cycling/05cycle.html

    The diagram accompanying the Times article isn’t as clear as it could be. Here’s a better diagram of the Gruber assist device:

    http://www.gruberassist.com/wp-content/5-technik02.jpg

    A comment buried deep below the Cozy Beehive post says that the Gruber device wouldn’t fit on Cancellara’s cycle, but then claims that there’s a similar device from Hungary that would fit.

    I’m also skeptical whether the boost would be worth the effort of dragging the extra weight around. (And if so, does that imply the Gruber device is a fundamentally bad product?) But to avoid maybe being too quick to debunk, note two things:

    (1) Isn’t it alleged that this is being used for the shorter sprint stages, not the longer endurance stages? For a short enough race, the balance tips in favor of using the device. Can we calculate what’s “short enough”?

    (2) Isn’t there a minimum weight rule for these bikes? Assuming the unmodified cycle is at the minimum weight , you could then add the weight of the motor + batteries, but then _shave off other weight elsewhere on the cycle that the minimum-weight rule would otherwise have prevented you from shaving_. If so, then maybe adding the booster and dragging it around isn’t the energy problem that it first appears to be.

  5. #5 dean
    June 8, 2010

    Even if the allegation is that these are used on shorter rides, I still don’t believe the extra weight would be worth the brief boost.

    There is a minimum weight limit for bikes in these races – I believe it is about 13.5 pounds, and many pro bikes push that limit. The examination of bikes pre-race can be extremely intense, although scales seem to have a disconcertingly large bit of variation.
    A couple years ago, in the TDF, one team using Cannondales or Treks (if I recall correctly) actually had to add a few grams of weight to get their bikes to meet the weight limit. I’m not sure how an engine, even if it were to provide enough aid, could be hidden during the pre-race bicycle examination.

  6. #6 Omega Centauri
    June 8, 2010

    If it is a time trial on flat ground, then I don’t think the extra weight would be more than a trivial penalty, i.e. well worth it. Even a one percent boost in sustainable output could make a very big difference. If you could disquise some photovoltaics (Bike Integrated Photovoltaics anyone), you wouldn’t even need a battery. A few watts could make the difference between a champion and an alsoran.

  7. #7 Eric Lund
    June 9, 2010

    @Emory: Even if the device is only used on shorter stages, that implies one of two possibilities: either the device (along with its attendant power and control systems) is removable, or the racer is using two different bikes, one with the motor for short stages and one without for the longer stages. I’m not sure whether the latter is allowed. A removable motor would have to be more easily detectable than a permanently installed motor because you could also detect it by spotting either the opening through which the motor is installed or removed, or the points where an installed motor would be attached.

    @ΩC: Even with photovoltaics, you still need some kind of conductor to carry the power to the motor, and a second (“ground”) conductor as a return. That means wires, which a bike inspector might notice.

  8. #8 KeithB
    June 9, 2010

    They switch bikes all the time, if a tire blows out, you switch bikes, you don’t fix it.

  9. #9 Markk
    June 9, 2010

    Even on a short time trial of say 20 or 30 minutes if you got a one percent boost in rider power you are talking about several watts say 30 watt hours. More likely you would need 100+ watt hours due to transfer inefficiencies, You only have a small number of square inches of area to get sunlight – those bikes are narrow, You are talking milliwatts of available solar power. So there would have to be a battery and you couldn’t have any kind of a real transmission as that would make way too much sound. Thus you are looking at some kind of system inside the crankcase or inside the cassette – those are the only places with any room that wouldn’t be noticed. You can’t have a thick rear hub. So some kind of system turning on and off a magnet every tire rotation I would guess, doesn’t sound too useful.

    By the way the races discussed were not short but the longest single day races there are – the classics, with cobblestones all over the place bouncing the bikes around enough to break forks sometimes. Not a nice environment at all.

  10. #10 richr
    June 10, 2010

    The UCI weight limit for bicycles is 6.8kg or 14.96lbs. (http://www.uci.ch/Modules/BUILTIN/getObject.asp?MenuId=&ObjTypeCode=FILE&type=FILE&id=NTI0MDY&LangId=1) There are bikes sold commercially at and below that limit, there are also shops that specialize in assembling the lightest parts available (these bikes often come in the 11-12lb range). The idea of this particular motor is to provide a 50 to 100 watt boost at a critical time, called an attack. An attack is a short accelleration with the intent to seperate yourself from the pack of riders. Even 50 watts is significant considering an approximate power output of 400 watts during a time trial at speeds of around 30 mph. I am not even guessing at whether this is what happened in the video, only that it is possible and why.

  11. #11 J.T. Wenting
    June 10, 2010

    “Even if the device is only used on shorter stages, that implies one of two possibilities: either the device (along with its attendant power and control systems) is removable, or the racer is using two different bikes, one with the motor for short stages and one without for the longer stages”

    This is exactly what riders do in multiday races with sprint and endurance stages.
    Not sure if Paris-Roubais has similar stages with different equipment in use, but if they have distinct sprint and endurance stages with each their own start and finish it may well be (there are also sprint events during the endurance stages, where the first X riders over a specific point on the course get extra points towards some reward on the finish line, switching bikes for those isn’t the norm if even allowed).

    “. Thus you are looking at some kind of system inside the crankcase or inside the cassette ”

    The batteries could well be hidden inside the frame, reducing the size penalty.
    Of course hiding the drive train from visual inspection would be tricky, anything that looks out of place would attract the attention of race officials so it’d have to look like it belonged there.
    And if it looked like it belonged there, where’s the thing that it mimmicks in looks?
    Say it looks like a brake assembly, it would then have to replace the actual brakes which sound rather dangerous (of course it’s theoretically possible to have a motor perform magnetic breaking, but that would increase the power requirements, thus increasing battery weight).

  12. #12 Jared W.
    June 10, 2010

    As a longtime cyclist and pro cycling fan, I simply don’t see this type of cheating happening; especially with Cancellara. It’s not like this is the first race Fabian has won. The guy wins races in A LOT of different scenarios. Most importantly, he’s a world champion in time trialing – solo races against the clock. We can talk all day about having switched bikes, a Hungarian version of the motor fitting inside his bike, and other hypothetical situations. The reality is that this guy is an incredible talent.

    As for that motor, the racket the thing makes when turning it on would be enough to give anyone away. Sure, races are noisy, but not THAT noisy.

    On the analysis, the difference in power outputs really isn’t that large. The difference is completely within the realm of possibility. Cancellara turns up the speed a notch and flies away from his competitors. If you watch the entire race, Spartacus did an excellent job of staying in the front, conserving energy, and keeping an eye on his rivals. When he saw that Tom Boonen (his only real threat in this race) wasn’t paying attention, he attacked. Bad for Tom, good for Fabian.

    A great race, a great analysis of power output, but certainly no cheating.

  13. #13 CCPhysicist
    June 10, 2010

    First, Cancellara is an amazing sprinter. I’d love to see the power meter output for him in real time.

    As others have noted, there is a minimum weight for the bikes used in competition. (I am told by an amateur racer that this is done for the same reason that NHRA does not let teams touch their rear wheels. There is too much temptation to reduce weight to the point where failures would be common and fatal.) It is also easy to make the bike lighter if you have enough money. For example, it is not uncommon for amateurs to spend thousands of dollars on a single bike wheel and tire combination. (The top end is $5,000 for one that weighs less than a kg.) It is quite conceivable that someone would remove weight in one place to make room for it somewhere else. They might already be ballasting the lightest bikes to keep them legal. That said, the race clip included a stretch on a really nasty road where a super-light bike might not survive.

    So I am not worried about his carrying extra weight. I’d be more worried about the claim of “no friction” from the bits that must remain attached to the drive train and would sap some energy for the duration of the race.

    Tech inspection can only catch what they look for. Now that they (and the competition) are looking for hidden switches, the magnets used in the motor, and the heat evolved from the batteries when in use, it would be a lot harder to get away with it. (Will we see a FLIR camera watching sprints? Someone tossing paper clips at the frame?) But people cheat in cycling all the time despite the risk of getting caught, so I consider anything to be possible.

  14. #14 Calibration Equipment
    March 10, 2011

    I am not really going to talk about the cheating aspect (my gut feeling says that it would be too easy to catch, so he is not cheating). This is exactly what riders do in multiday races with sprint and endurance stages. Calibration How light could the engine be, and would it provide enough oooomph at the equipment critical time to justify carrying the damn thing for the rest of the race?
    Calibration Equipment