Team Sky released some of Chris Froome's power data from stage 10 of the Tour de France in an attempt to end speculation about doping

This year’s Tour de France has been dominated by arguments among pundits and former riders about the plausibility of the performances of Chris Froome and the rest of Team Sky.

In an attempt to address some of the questions, on the second rest day of the Tour the team’s head of athlete performance, Tim Kerrison, provided some of the team’s data to journalists. It was from the climb to La-Pierre-Saint-Martin, where Froome took a stranglehold on the race on Stage 10.

“It’s a about a 15.3 km climb,” said Kerrison. “Around 41.30 [in duration]. Chris’s average for the whole climb was 414w, and a VAM of 1602 Vm/h.”

VAM is a measure of climbing speed, measured in metres-per-hour. The biggest values ever seen in pro cycling, over sustained climbs, were in excess of 1800 Vm/h, from Lance Armstrong and Marco Pantani.

>>> Chris Froome in Tour de France ‘dream position’ despite criticism

At the other end of the scale, the grupetto on a climb like the Col du Soudet would be more like 12-1300 Vm/h. 1600 Vm/h is much closer to the climbing speeds seen in the pre-EPO era – although accurate VAM data is not always easy to come by, since it’s frequently calculated from historic TV coverage.

Asymetric chain rings mean that our power values over-read by about 6%, so corrected for that, his power-to-weight was 5.78w/kg,” he continued. This means that Froome’s corrected average for the whole climb was more like 390w.

“His average cadence was 97 rpm – his gearing was 52/38 and 11-28. His average heart rate was 158 bpm, and his maximum was 174 – that equals the highest heart rate we’ve seen from him over the last few grand tours.”

Chris Froome wins stage 10 of the 2015 Tour de France (Sunada)

Chris Froome wins stage 10 of the 2015 Tour de France (Sunada)

The data Kerrison presented for the full climb certainly appears to pass the plausibility test – it adds up with what we saw on the day. The problem is that it’s almost impossible to jump from there to any realistic physiological data.

Even attempting to calculate something like VO2max – the “golden number” that everyone has heard of – is impossible, because it requires assumptions about relative anaerobic and aerobic contributions to the climb, the proportion of his maximum that Froome can sustain, and his own efficiency. Kerrison pointed this out himself.

As for the Stage 10 data, Kerrison went on to discuss Froome’s attack. “The attack lasted for 24s,” he said. “The average for that was 556 w [522 w corrected] and the peak was 929 w [873 w corrected].

“To put the attack in context, in the four minutes leading up to it, when he was with the other contenders, his power was 449 w [422 w], and his VAM was 1777 Vm/h. After the attack, his power was 435 w [408 w], but he was still riding away from Quintana.

“Compared to what he’s done in the past, his maximum 30-minute power on the climb was 419 w [394 w], and Chris has exceeded that, by as much as 10%, on as much as 16 occasions in recent years in racing and training. His 60 minute power, which includes the lead into the climb as well as the climb itself, was 366 w [344w], and he’s exceeded that on 15 occasions.”

Expressing the data in relation to previous rides may be a pointer as to how Team Sky feel data might most usefully be deployed – as a sort of power version of the existing bio-passport which works by looking for dramatic changes in an athlete’s profile rather than relying on comparing single outstanding metrics against an ‘average’.

At the same press conference, Sir Dave Brailsford suggested the UCI might think about getting teams to provide power data to an expert panel to create just such a system.

The team will be aware that releasing selected data to journalists in the middle of a race is unlikely to put an end to the speculation. But they will certainly be hoping to have made a worthwhile start.

Chris Froome’s Tour de France bike

  • So, all data presented by Sky lead to an average climber! In this context, seems that Contador and all the others are pretty low and poor cyclists, and Sagan, Talansky I think that I can leave them behind!

  • Margaret

    Oh dear.. I hope the lab results for vitamin deficiency prove more reliable.. All that hard work done by students at Leicester university to establish whether or not winnie the pooh had a vitamin B12 deficiency are reliable is concerning… Not to mention the tooth decay…shocking

  • pilot101

    Is he riding the same bike as Lance did on that climb, does he have the same nutrition technology and other exercise regimes. Is he perhaps more dedicated to the race? How come people have gotten faster and faster at running the 100m in the last year, everyone who ever beat the first person to take a timed 100m run must be doping as well.

    Also climbing isn’t everything in the GC is it?!

  • Dr. Malcolm Robson

    VO2 is useless measured in a laboratory compared to actual road, it’s only a measure of pulmonary function. Unless you test for Biochemical indices, like lactic acid and prove the physiology, there will always be suspicion. I am surprised that the team staff are not measuring biochemical indices that would prove this one way or another

  • Craig Ross

    How do you know I “..have no physiology education”? I’ve got four university degrees, and while none of them are in physiology I know enough about reading, reasoning and writing not to take to the web with a chip on my shoulder and a load of unfounded speculation. Is it the case that you inherited a small “motor”, can’t tolerate discomfort, can’t train hard and can’t control your diet? The reason I ask is because it would be a pretty good explanation as to why you’re throwing around a load of idle speculation about Froome with no basis in fact whatsoever. I was on the Wattbike yesterday – fifty years of age, with twenty years of decline since my 5.02 litre Douglas bag run-to-failure test. I did a 30 minute interval session, with the recoveries the same length as the efforts. Five two minute efforts above 46k and five more one minute efforts above 47k. So, basically, ten 400W efforts. Froome is two decades younger than me with a bucket load more talent and nothing to do but train. You probably can’t wrap your head around what he can do because you can’t do a decent fraction of it yourself. If you’re bitter and twisted why not keep it to yourself.

    [I also note that Eddie Santos PhD looked at the numbers and concluded, “Froome averaged 6.06 W/kg over the penultimate 14.4 km of La Pierre-Saint-Martin. At a recently reported mass of 68 kg, this amounts to 412 W over 38:15.”

    412W. 412W. You turn the pedals at 412W and think, “Could someone really talented sit at this level of power output?” And the answer is, “Easily”. Old men (like me) can do 3/4 of it. Sorry. Some old men. Old men able to engage with the world and make the effort because they aren’t expending all their emotional energy slagging other people off].

    Six litre guys are rare, but we’re talking about 150 people from seven billion. Every cycling club has 5.3-5.5 guys. To repeat – because you don’t seem able to grasp it – 350W on a bike is only 4.58l of oxygen. If you are playing with nearly six litres and have off-the-chart efficiency then you can sit at over 400 and there’s nothing to explain. Froome and the other leaders are distinguished by having the ability to sit at (say) 5.3L just using their legs on a bike, something you can achieve if you’ve nearly six to start with and train all day.

    You bang on about the need to measure metabolic output when (of course) what matters is useful work done.

    You talk about Froome being lighter, but with your expertise you’re presumably familiar with the obvious fact that cyclists train precisely so that they can do what rowers and people who need to run on treadmill inclines can’t – use all the oxygen they’re ever going to be able to deliver using two quads and nothing else. I know a cyclist who is 62kg at six foot two: he looks like a picture from a Japanese camp and can still deploy those two skinny quads to maintain silly heart rates. That’s what cyclists do – it’s their thing.

    You think Wiggins picked a pace that could have resulted in blowing up? Er, yeah mate. Doing your absolute best means setting off in the full and certain knowledge that you might hit thirty five minutes and find you’ve nothing – on that particular day – left to give. Wiggins would have known to within a watt what he could reliably do. Sitting at high percentages of capacity is unpleasant for everybody, which takes me back to my first point: athletes are born not made. Wiggins found the hour record horrible because there’s little reason to suppose that his tolerance for that kind of horror is any greater than the thousand people who will ride up and down a bypass in Britain tomorrow morning.

    The VO2 max test/Douglas bag/Cooper test research was Grant, Corbett, Amjad, Wilson, & Aitchison (1995). A comparison of methods of predicting maximum oxygen uptake, British Journal of Sport Medicine. I was one of the “physically active members of the university community”, because I knew Kenny Corbett from the running club. He’s working in New Zealand now, I believe. The kid with the 80ml score was one of the guys in the Hares and Hounds. I shouldn’t name him but he could run about 4:15 for 1500m and was a renowned waster – flitting between the athletic club and the road running club, known by everyone to be talented beyond belief and totally unable to get a grip. [Just checked – he ran 3:54 for 1500 at about 18 years of age]. He trained with a bloke who scored 64ml on the Douglas bag run-to-failure: 64 plus some guts was as good as 80 and none.
    You’re just a bitter bloke libelling someone without any evidence because what they can do is so far away from what you can imagine that you refuse to accept that it’s possible. It has been well said that nobody can imagine anyone doing anything for a reason that they couldn’t have. It’s also true that there’s a cohort who can’t accept that some people can solve Rubik’s cubes in fifteen seconds, run four minute miles, solve maths equations, write symphonies……………….all because they can’t.

    .

  • JGault

    Craig this will be my last correspondence with you. I will touch on a few specific points in your reply.
    It’s a phrase. I was trying to be polite and not come right out and say you have no Physiology education just an incorrect opinion. 6 liter guys and 80 plus Vo2 Ml/kg/min guys are incredibly rare. 7watts/kg at threshold is even rarer.

    I was politely trying to explain to you that 7watts/kg is at THRESHOLD NOT MAX. (Multiple terms are used for threshold these days) which you incorrectly tried to compare with using a MAX ramp test.

    I was politely trying to show that you are mixing tests. You’re mixing formulas and your mixing results. Ramp tests by virtue of their name do not analyze gases. Beep tests which you also reference do not analyze gases. At this level ONLY a MET cart would be a valid tool for measurement.

    “Given that we’re talking about the most freakish people on the planet their performances are nothing extraordinary”.

    We aren’t talking about comparing Froome to your UNI boys. We are talking about Chris Froome destroying the best collection of climbers at the tour in past 10 years. A super extraterrestrial Freak toying with the best earth bound climbing freaks. I will admit that it is only opinion, mine and many other who are skeptical, Froome appears to be holding way back ever since he basically won the race on stage 10. The skeptics would love to see the data on the other climbing stages and see how low Froome’s HR/wattage is compared to his competitors and his stage 10 performance.

    I venture no one on this forum except you believes that Wiggins could set the hour record after 4 plus hours of a climbing stage at the END of the race on the LAST summit climb. That was my comparative point. I guess i didn’t make that clear for you even though you did understand that the specific performances were Iconic.

    A further comparison, had you bother to read Froome is 5 kilo lighter with similar body fat %. That’s a lot less muscle pushing similar wattage at the end of a 4 plus hour climbing stage. That is quite a CV system.

    You’re out of your mind if you believe Wiggins paced himself to just beat the current hour record. But don’t believe me. Wiggin said his goal was to put the record out so far that it would last for 15 years. He also said his goal was to go about a Kilo further. There goes your stated Idea that he could go further if incentivized. He also said it was the hardest thing he ever did.

    I have an undergrad degree in Exercise Physiology and am a retired physician. I am quite familiar with students work in the lab. Since you say that work at Russell Group university was published please reference the material.

    I look forward to reading about all the 6 liter recreational athletes milling around the campus.

    I will mail you $50, euros, pounds whatever. if you can show me a published abstract of an 80VO2 ml/kg/min human being with their body fat @ 20% or higher at the time of the test as you stated. heck i will make it $100.

    Oh and it doesn’t even have to be the nonexistent guy referenced at Russell Group University.

    No one cares about YOUR weight. Please

    The article i referenced was produced by one the leading EP’s in the elite competitive sports field. The guys at sports scientist have forgotten more about cycling performance than you will ever know.

    “Incidentally, this link doesn’t really amount to anything”

    Well well, Look what is the lead article at Cyclingnews today. Guess it amounted to quite a bit.

  • eminusx

    Armstrong fanboy? How’s that? did you actually read what I said and understand my point? My point is that just because someone outperforms somebody else it doesn’t automatically mean they’re doping, it isn’t beyond the realms of human performance to do so, so tell me that statement is false…..

    FYI I despise that cnut Armstrong

  • Craig Ross

    The only way that rings can give an advantage is by allowing a cyclist to get nearer their absolute ability. Cycling is a sport of local muscular endurance in the legs more than absolute oxygen consumption, which is why even elite cyclists could probably maintain a higher percentage of their VO2 max for longer on foot (assuming they’d been given time to learn to run). So what an Osymetric ring actually does is give you the chance to produce something more like a stamp, which means you can get more out of what you have. I’d wager that such rings have a bigger percentage impact with less experienced and younger cyclists, and probably also triathletes. Older and more experienced riders probably have enough local muscular endurance in their legs to use everything they’ve got.

  • Craig Ross

    Incidentally, this link doesn’t really amount to anything.

  • Craig Ross

    I’m not mixing metaphors because I’m not using metaphors. You could argue that I’m eliding over distinctions that matter, but I’m aware of the distinctions and didn’t fancy burning 500 words making that clear.

    My weight hasn’t moved in thirty years and nor has my percentage bodyfat: okay, being entirely honest immersion weighing with gas analysis in 1994 and bio-impedance in 2014 gave the same figure.

    Lab performances in students when the students are Russell Group university students doing intercollated exercise physiology degree, the lab work supervised by the staff and the results published, can be trusted. Wiggins and Froome are basically identical in absolute output, with Froome shading it per kg and with the deadspot in the hills and Wiggins marginally the better time trialist. Wiggins’ hour record was paced to produced a guaranteed success: if he’d been offered a hundred thousand pounds for ten yards further he’d have set off a lot quicker.

    Within a margin of error what you’re actually saying is that Froome can do in the middle of a race what Wiggins can do when trying to engineer a specific outcome, when they both have roughly the same ability. The Wiggins effort is measured to produce a good but not best ride and Froome is going mental while full of adrenaline in the middle of a battle. Err….yeah!

  • Osymetric Aust

    I think everyone is missing the point. The so called 6% over statement of Froome’s power because of the Osymetric rings is false. The tests I have done do not overstate actual power at the back wheel, it is a real power advantage. The reason is that there is less energy wastage at top and bottom points of the pedal stroke and more power on the downward points of the pedal stroke. The only reason that more pro riders do not use them is because of sponsorship issues. Take a careful look at the number of riders using Q-Rings, there must be something in non round rings. I can declare a vested interest, I am the Australian importer of Osymetrics, none the less, if Froome wins, that will be three out of the last four TDFs that Osymetric have been on the top of the podium! Cheers – Barry

  • Phil

    Can you point me to the power record for these riders and the model applied to these records. Basically – please show your workings. Normally you would expect someone cheating to have higher power so I’m not exactly sure what the accusation here is. The Doctor mentioned having to rule out a motor (which I’m sure is purely academic) but maybe the insinuation is tampering with the data? In that case why would they tamper with it in a way that was easily spotted, why not just make it match these models? But that is speculation because I’m not sure what you are implying.

  • JGault

    It’s a smokescreen.

    The other riders also released their data for that stage. I don’t know if Froome is doping but i do know Sky is lying about their data.

    Great article explaining what many have been saying.

    http://sportsscientists.com/2015/07/great-power-great-responsibility-less-power-greater-speeds/

  • JGault

    stupid. Sounds just like an Armstrong Fanboy.
    Well said orbifold.

  • JGault

    every rider who released their data for that stage matches the Models. Froome’s is the only data that does not match. his “Adjusted” wattage is lower. That is peculiar stacked on a peculiarly awesome physiological display.

  • JGault

    Yeah, Tim has no reason to lie. Err, well he just wouldn’t.

  • JGault

    you’re mixing metaphors VO2 max is different than VO2 ml/kg/min but related. 7watts/kg is independent from VO2 & VO2ml/kg/min.

    You may be able to do 300 watts for an hour at 50yr s old but i bet you weigh more.

    I am not disparaging you or anyone else but i have to question lab performances executed by students on random subjects and self reported PR’s. At the high end i would never trust a beep test or any other corollary. For these guys a MET cart is the only acceptable test. I am sure you have seen all of the fake Strava performances. I myself made huge errors when first using a MET cart in the mid 80s.. The technology is dramatically different now. Also errors are much less dramatic and less frequent.

    Bradley Wiggins just set the hour record.. It is reported he weighed 72kg and rode at roughly 450watts. Thats with a proper PLANNED warm-up, a controlled environment and predetermined set time of 1hour.

    Take Froome’s data AFTER sky down graded the wattage by 6%. In the second half of the climb He rode more than 20 minutes at roughly 440 watts with a huge 500plus watt 1 minute attack right in the middle. He dropped back to roughly 440 watts for 10 minutes after the attack which to me is the most amazing physiological part of the performance.

    I have Froome at 6.7watts per KG based on the Adjusted numbers sky released. ( i am counting the last half of the climb ONLY not the first half)

    This is after 4 hours in the saddle of a tough climbing stage.

    Froome last 20 minutes 6.7watts per kg with a 1 minute 7.5 burst in the middle.
    Bradley Wiggins hour record 6.2 watts per Kg. for 1 hour. 450 watts 72kg.

    Wiggins stated this was the hardest thing he has ever done. History shows how epic his ride was. That should give you perspective on the Froome performance.

    The other puzzling thing on Froome’s ride is that all of the Models VAM, p VAM, etc.. are extremely close to the actual data for the riders who released their data on that stage. The models however don’t match Sky/Froome’s data that was released.

  • Craig Ross

    At 80kg 350 watts is “only” 56ml per kg – 4.5 litres (IIRC). The point I’m making is that people you’ve never heard of, who are very good amateurs (50 miles in two hours) can sit at way, way over 300W. The Wattbike website is full of performances from nobodies in leisure centres – and I doubt they are all made up – that make it pretty obvious that you don’t have to be too many standard deviations away from the norm to be near where these guys are. Given that we’re talking about the most freakish people on the planet their performances are nothing extraordinary. Chris Langan – the IQ guy – is far more impressive than these sportsmen. There are plenty of people with high oxygen consumption figures. The UK won all those “sitting down” gold medals (rowing and cycling) by putting up adverts in universities and testing people who came forward. I’ve seen someone reach level 18 on the beep test. I was at university with a loser who had 20% plus bodyfat and still had a VO2 max above 80 per kg – a local hero and nothing more; too indisciplined to work.

    Froome’s figures just aren’t that remarkable. He may have been “riding for hours” when he goes ballistic, but 400w for the guy in front is 200w behind him and 160 for third in line.

    At fifty I could do 300 for an hour if I set my mind to it, maybe more. That’s from 5 litres at 28, so (probably) I’m on no more than 4.5 litres. If you’ve a VO2 max of nearly six litres and you’ve nothing to do all day but train is it really so surprising that you can do 300 plus a third and a bit – 420?

  • JGault

    Craig,

    sorry but 7 watts per Kilogram for 40 minutes is Stratospheric. It’s like seeing bigfoot and a unicorn on the same day. A 6 liter guy is almost as rare. I’ve only seen 2 in over a decade of testing. Both CX skiers. As a former EP I can tell you I have test many people who fail at (reach would be a better word) 400 plus watts on a ramp test. Few if any were 6plus watts/kilogram guys. Remember a ramp test is to to failure, last maybe 25 minutes Depending on the protocols , and starts at a much lower wattage. These guys are averaging 420w at threshold after riding for hours.

  • Paul Jakma

    425 Watts in a ramp test doesn’t compare with 400 Watts average sustained over 40 minutes. An athlete who can do the latter can probably hit 470W to 500W in a ramp test, maybe more.

  • Darkhorse

    Ehh….I’ve trained with a meter for years and climbed all of those mountains in extreme temps and cold/rain. The only variable that stays the same is the 10% grade prior La Mongie on the Tourmalet. Once you have experienced those, you dont need a meter to tell you what 7 mph or 10 mph or 12 mph feels like…..well I’ve never felt 12 mph on 10% climb.

    14 mph or thereabouts gets people’s attention….power meter or not.

  • Craig Ross

    I’m a fifty year old knacker. When I was very fit aged about 28 my VO2 max was just over 5 litres, or nearly a litre less than it would have to be for me to be really good. At the moment I train on a Wattbike three times a week, which measures power to within one percent. I can sustain 306 watts for twenty minutes – although I’m rubberized at the end of it – and 360 watts for four minutes. When I was at uni a good amateur cyclist was measured in the lab as having 7 watts per kg and a ramp test score of 425 watts.

    In other words, most elite athletes just aren’t doing anything that they shouldn’t be able to do. Indeed weeks of uni physiology tests demonstrated that a lot of elite athletes, including people on Scotland’s Commonwealth Games team, couldn’t go beyond their anaerobic threshold: they gave in when it became painful. Athletes are born, not made. They don’t train any harder, or suffer any more, than amateurs who were born with less ability. You’d be as well admiring tall people for their height.

  • eminusx

    Yeah it seemed like that could be a logical answer. The ring shape would affect the chain tension/power delivery and be picked up the power meter, which begs the question, what is the advantage of this, both physiologically and in terms of physical travel

  • Lee Wingate

    Darkhorse – that is a ridiculous statement! takes no account of headwinds, tailwinds, environmental conditions and a whole host of other factors. Irks me that people who have had a powermeter for 1 yr, think they know better than someone llike Tim Kerrison who has 10yrs + degrees specilising in this type of data.

    In addition…. the power data is not unrealistic at all for an elite rider!

  • Lee Wingate

    As an Engineer, I can confirm that essentially that is correct. the angular velocity changes and it is this value among others that change the strain values measured on the crank.

    it actually doesnt matter if the strain gauge (power meter par se) is in the pedal, crank or ring… the values measured are the same essentially. but oval rings will change the values and cause over-reading.

    Interestingly, oval ring makers claim an increase in power of between 2-6%!!! so essentially, it could be argued they dont actually make any difference whatsoever.

  • Jsmith

    A French so-called expert who is giving the French media the benefit of his wisdom was interviewed on radio last night. He has calculated the data and concluded that Chris is with certainty doping no question about it. However he did say that if Chris is an exceptional athlete his calculations would be wrong. Ruin a man’s career why don’t you. Without the full facts you cannot calculate anything and Sky quite rightly will not provide those details during the tour.

  • Phil

    So what you are saying is that there is an arbitrary climbing pace that if you go faster than you are probably doping. Why not go back through the history books and convict everyone based on previous times? Pretty obviously it is hard to compare the exact same climb on different years let alone different climbs. The race day tactics, the weather and the effect of the other racing days will all factor in. These aren’t climbs in laboratory conditions in isolation of all other cycling.

  • Fra Cazzo da Velletri

    Hmmm … sometimes the word “dope” needs to be used in it’s original context.

  • Kaptain Fries

    why is it this cycling organization are always got a negative words towards there athletes, after all of those Armstrong era they would publish to world that cycling had cleaned up, as they have bright scientist and labs to get the cheater,its seems to me that they are the one giving a sport of cycling a bad name, On my owned understand this riders got tested almost every day, Maybe should not invite the world to ride there race, just let all the french teams ride, then finally a french cyclist won the race, and see if the word “DOPING ” well come out or they still this billion of data,

  • orbifold

    If your niece, dad and you are below 10 sec in the 100m race, I would start suspecting.

  • eminusx

    ….and I run faster than my dad, who is faster than my niece….so I’m obviously doping. But my dad is likely doping also because he’s faster than my niece, which is inconceivable without the use of drugs right?

  • fre

    sorry, I still think, that this 6% difference is bullsh** , because Stages measures power only on the left side, so the asymmetric chainring does not have any meaning… or is the chainring now on the left side?!?!

  • Darkhorse

    I got a power meter lesson last year at the Tour from some data experts. In spite of all this technical talk and expensive meters, power output is not a measured output but rather a mathematical calculation of many variables. The reality is Froome averaged 22 kph for 41:30 on a climb comparable to alpe d’huez where Lance average 21.5 kph for 38:00. Decide for yourself.

  • JGault

    wouldn’t THE MOST ANALYTICAL CYCLING TEAM calibrate with the OSY RINGS. My understanding is that they only overage when calibrated with round rings then swapped out with OSY rings.

  • JGault

    First thought Sky doesn’t use SRM they use Stages meters.

    SRM measure at the spider. Stages on the left Arm. (new versions on both arms)

    According to SRM the OSY RIngs measure higher IF, IF your calibrate with ROUND rings then swap out OSY RIngs. Would an outfit like like Sky screw up their calibration. NO unless they Calibrate with the correct rings so they can SAY there is a 6% overage.

    Finally for anyone who digs deep into power meter files you know you can easily pull a raw file as an excel file. A child can enter a simple formula in excel to change the every data point by a set percentage then convert it back as a .fit (powermeter) file.

    Someone needs to calculate the difference between the estimation models and the wattage data. Bet their off by 6% or more..

    Also they should have these guys weigh in before and event.

  • ThePollitikat

    You might be on to something. The on off delivery of power might simulate a motor…. A motorised crank? Lol…I am not accusing just trying to understand. I do believe in science and data and the benefits of using data to enhance performance.

  • Mike Prytherch

    Typical forum experts ! the most analytical cycling team would of had years worth of power measurements across many platforms, I suspect they know exactly the differences between rings, power meter manufacturers etc., for example they would of almost certainly had to go back and recalculate power readings when they switched to Stages so they could compare, so I’m 100% positive they measured power readings for normal and asymmetric rings, perhaps I’m Mr Naive but I believe him, its what he does for a living and not what any of us do.

    I’m also sick to death of hearing about cheating, how can you prove you are not cheating, you simply can’t, can the press and anybody else please stop, its spoiling cycling and spoiling the tour, if you think they are all cheats go and watch football instead.

  • eminusx

    I’m no expert, far from it, but is it because the power is delivered in waves, not as a constant, hence the sum of peaks and troughs is the average power value, but the peaks indicate a marginal gain in power by virtue of the on/off delivery?

    More of a guess than anything to be honest. . . dudes on here know far more than I do!

  • enjo

    They do use the Stages, so your question is well-put. Anyone have thoughts on how the asymmetric ring would affect readings in the crank arm itself?

  • fre

    I thought SKY is usign Stages Powermeter? an asymetric chainring in this case, in my oppinion, does not change anything… correct me if i am wrong…

  • Ambientereal

    Froome used an 6% eccentric chain-ring, so it is expected that a 6% overestimation in Power appears. In fact power meters measure instant force in the pedal and cadence. The torque is evaluated considering a given ring diameter. For precise evaluation, the force should be measured in the chain directly.

  • Vertigo

    Thanks/ Yup looks like Q-rings aren’t a trade secret at all. Perhaps he’s got something hidden in those elbows..

  • Paul Jakma

    The powermeter measures strain (deformation of the material) in a crank or spindle. Strain relates directly to force. Power is force applied over distance or time. One way to measure this is to measure the cadence. (Measuring the cadence is self-clocking, while measuring time directly is much harder to do accurately and reliably, I suspect).

    What I gathered from an engineer at a well-known power-meter company is that some power meters sample the cadence to rpm accuracy, or otherwise reduce it to rpm accuracy in their calculations. The issue appears to be that, for the same rpm, crank rotation speed can vary significantly within a rotation with oval rings compared to round rings. This means the peak force might be happening over a shorter rotational distance with an oval ring, while the power meter assumes it was applied over a longer distance. And so it calculates a higher power than true power.

    The power meter engineer I spoke to told me this has been shown to lead to about a ~2% overestimation of power.

  • Steve

    From an article in March

    The credible tests and research that has been done is inconclusive, according to Kerrison: “Crank-based power measurement systems [e.g. SRM, Quarq] appear to over-report power when using Osymetric rings, which is probably due to the variable angular velocity of the crank throughout the pedal revolution. In other words, power reads higher, but this does not correspond with an increase in the power actually being generated by the rider.”

  • Horace Ho

    Force cause crank to shape shift. The shape shift is described in terms of strain. Power is measured as strain (shape shift) experienced by the crank on a stage power meter. They calculating force & hence power based on strain (obtained through sensor reading) on a processing unit. It could be the case of crank experiencing more strain giving same amount of force for a Q-ring set up.

  • Vertigo

    Fascinating.
    Why would asymmetric rings exaggerate the measured power? Is it instead that they increase actual power over circular rings by 6% so TK made the adjustment to allow physiological comparisons without the mechanical difference. It’s not that oval rings are new, but perhaps Sky have given away a trade secret here!