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  • slowbikeslowbike Posts: 8,494
    slowbike wrote:
    Possibly under-estimated my weight and you need to take into consideration temperature and wind (it's an exposed hill).
    So it's not a million miles out ...
    20% difference is quite a lot isn't it?

    1) under estimated weight on Strava - commute home would've been at the end of the day - possibly carrying backpack, a bottle of drink, saddle bag, pump - everything you need for self supported short ride (it was over 2 years ago I can't remember!) - the later ride was a hill climb - so strip everything off to the bare minimum - worse case is a 0.9 mile walk ...
    2) weather - 21st May vs 2nd Nov - May is going to be warmer for sure - warmer air is less dense. I remember the TT being a headwind and not very nice weather.

    Does that add up to 50w ? Dunno - probably not - huge variances in the calculated power on strava for the same time as me - one other power meter recorded ride at 345w - I guess he's heavier than me then - or had a massive headwind....

    Oh - and Strava segment don't work on the exact start and end point - just the nearest ...
  • craigus89craigus89 Posts: 887
    If Strava knows everything needed, including the weight of your bike AND if you have a reliable segment and trace, then the number it churns out should be reliable. Problem is a lot of segments are not what they seem and others are not meaningful for the purpose of measuring a VAM or power output.
    Round here (Warwickshire) there are two climbs which I think are perfect for the job as they are both steep and regular: "Edge Hill" just off Kineton and Dovers hill from Weston Sub Edge. My time up the latter varies between 7 minutes and 7:15, which means at best we are looking at a VAM of 1150 mt/h, which in my case means just under 300 Watt.
    Bear in mind this is not fully aerobic, as I would not be able to go at that pace for longer... for longer fully aerobic climbs (which are hard to find in the UK) we are looking at 250-260 Watt and a VAM of 950-980 mt/h

    So does anyone know how Strava uses elevation data for these calculations? Presumably the only way would be the difference between the start and finish elevation so that any dodgy data in between wouldn't be taken into account and it would know the avg gradient from that?

    There is a hill around me that I just checked back on, I put in an effort up it taking 6:17 and according to a couple of calculators online I was putting out around 290 watts, but the strava segment says avg 236 watts. Also my VAM seems quite low at 812 for that climb according to Strava. But then checking other hills that I haven't put in an effort on some are showing a VAM in mid 900's.

    Maybe I'll go trawling through the Strava help pages and see if the calcs are on there. Not that I'm that bothered, just curious.
  • ugo.santaluciaugo.santalucia Posts: 25,265
    craigus89 wrote:
    If Strava knows everything needed, including the weight of your bike AND if you have a reliable segment and trace, then the number it churns out should be reliable. Problem is a lot of segments are not what they seem and others are not meaningful for the purpose of measuring a VAM or power output.
    Round here (Warwickshire) there are two climbs which I think are perfect for the job as they are both steep and regular: "Edge Hill" just off Kineton and Dovers hill from Weston Sub Edge. My time up the latter varies between 7 minutes and 7:15, which means at best we are looking at a VAM of 1150 mt/h, which in my case means just under 300 Watt.
    Bear in mind this is not fully aerobic, as I would not be able to go at that pace for longer... for longer fully aerobic climbs (which are hard to find in the UK) we are looking at 250-260 Watt and a VAM of 950-980 mt/h

    So does anyone know how Strava uses elevation data for these calculations? Presumably the only way would be the difference between the start and finish elevation so that any dodgy data in between wouldn't be taken into account and it would know the avg gradient from that?

    There is a hill around me that I just checked back on, I put in an effort up it taking 6:17 and according to a couple of calculators online I was putting out around 290 watts, but the strava segment says avg 236 watts. Also my VAM seems quite low at 812 for that climb according to Strava. But then checking other hills that I haven't put in an effort on some are showing a VAM in mid 900's.

    Maybe I'll go trawling through the Strava help pages and see if the calcs are on there. Not that I'm that bothered, just curious.

    The VAM is an easy number to calculate, you only need elevation and time... if that is wrong, then it's not a good starting point.
    Does Strava know the weight of your bicycle as well as your weight? That matters, unless it defaults to some random number like 8Kg or even worse does not include it at all
  • bflkbflk Posts: 240
    Alex99 wrote:
    craigus89 wrote:
    [*]
    for a decent estimate of power output without spending money on technology, you need a hill... the longer and steadier the hill, the better and with a gradient of at least 6%.
    You then plot your time against the hill elevation, your weight etc in a calculator you can find online and you get a fairly accurate estimate of your power output based on simplified physics. You will find that as far as aerobic output goes (which means you can sustain that effort for at least 20 minutes), you are probably somewhere between 200 and 300 Watt depending on your level of fitness, higher if you are a well trained athlete, lower if you are a novice (or you are very small).

    Hmm, is that not what the Strava power estimates are? Presumably that is done via a basic calculator like you mention, but people are always saying they are pointless and not worth looking at.

    Strava power estimates on hills can be OK. It depends on how good the topographical data is and how good your GPS trace is. The point it, if you have a local hill that you know is 8% for say, 2k, you can get a decent measurement using a stop watch and a calculation.

    The main problem especially where I live is the wind. Our local classic climb (the Crow Road) goes roughly NW and for most people including myself our PRs were all set on days with freak easterly tailwinds. Usually there is some degree of headwind. So my Strava PR which is just on 200W estimated may be a bit flattering. That''s why I thought an out and back flat course might be more useful.
  • Omar LittleOmar Little Posts: 2,040
    bflk wrote:
    On the basis of a local 7M TT course which is flat and out/back I am likely producing <200W (or even << 200W) riding solo on it (ie not an actual TT). That's estimated from data from the riders who have power meters. It takes me over 20 min so for me roughly corresponds to the 20min power test (obviously the top guys are more like 14/15 min though). I weigh 62kg. My bike setup and riding position is probably poor so I'm not that bothered really.

    https://www.strava.com/segments/1246484

    With it being a TT course many of the times there will be set on TT bikes, so you might not be as low as you think. I know the road quite well and i dont think 200 watts for 20 minutes on a road bike with a non aero position would be a million miles away.
    paul2718 wrote:
    I averaged 710W for 30s at the end of a race this evening. All that matters is that it wasn't enough.

    Boardman's comparison seems about right, but I think 800W might be an over-estimate. I found an old paper from 1996ish that suggested that for 60kph the powers for the four would be 607W, 430W, 389W, 389W. This would seem to be a good ball park even today.

    Paul

    World record is about 10 seconds faster than in 1996 - and they would have been using the superman position back then too.
  • paul2718paul2718 Posts: 471
    Alex99 wrote:
    They're going faster than 60 these days :shock:
    About 62.5.

    All else being equal that would put the lead rider on 686W. But we know that the equipment is better.

    Paul
  • ugo.santaluciaugo.santalucia Posts: 25,265
    paul2718 wrote:
    Alex99 wrote:
    They're going faster than 60 these days :shock:
    About 62.5.

    All else being equal that would put the lead rider on 686W. But we know that the equipment is better.

    Paul

    I also thought 800 did seem excessive, but I had no basis to think that
  • AnonymousAnonymous Posts: 28,799
    philthy3 wrote:
    bflk wrote:

    Functional Threshold Power of FTP and watts per kilo is a good indicator of someone's ability.

    Screen_Shot_-_Power_calculator.1408529835.png

    power-profiling-chart.gif

    This is the most important and accurate figure to aim at. If I do an FTP and average 250 watts and the guy next to me does 300 does that make him stronger/fitter than me? It depends on the weight, age, body shape. I know loads of people who will kick out a better FTP than me but when it comes to actually riding in the real world they are slower. Longer limbed, taller people will have an advantage over me here but only here where there is no hills or wind to push against.

    Why? I am around 5'7" and 66kg. I have a reasonably good watts per kilo average (around 3.7 to 3.8 ) and I will always beat some heavy stomper up a hill. Unless you live in Norfolk or Lincoln there is a decent chance you will hit a climb sooner or later. I also create a small frontal area so I am a lot more aero than most. I can get low down and cut through the air better. This also works to my advantage as I can sit behind a big guy and draft but I am of no use to him doing the same to me. In a flat race I will always be beaten by someone who can churn out 50 watts more than me but in the real world that does not happen very often. Hence why big muscular riders with lots of power only are good at one thing and thats sprinting. Why do you think Someone like Cav or Greipel get left well behind on anything other than a flat as a pancake day?

    If you can improve your watts per kilo average this will make you faster more than just raw power. Losing weight will in my eyes always trump more power if you are only using that extra power to push a heavier bulkier frame through the air.
  • okgookgo Posts: 4,368
    Boardman was bang on.

    For anyone even slightly alright on a bike (unless they're under 60kg) 160w is pootling.

    Re powers required, given Wiggins etc could do 570w for the individual pursuit, I should think about 700w on the front is about right, though some riders do longer turns than others. Clancy would find 700w very very easy, while it may be harder for Wiggins, but he could hold 600 for quite a long time, and Clancy being more sprinty probably burns off quicker.

    I would also say that the chart above is probably not all that accurate given its got me as Div 1 pro, and I'm actually a 2nd cat. Also on most roads in the UK - w/kg less important that having more watts, we don't have many long climbs. Good example was a clubmate of mine who is VERY light did 5.5w/kg for 25 minutes yesterday in the National 10 mile time trial and came 50th, I did less than 5 w/kg and was 14th and it was on a rolling course too.

    People read about pro cyclists and their obsession with w/kg and then think it makes any odds to the riding they do round a largely flat country. You'd be far better concentrating on generating more power, Cancellara/Boonen/Stannard all over 80kg, and all do well in races that are more similar to the terrain in the UK (with a few exceptions of course).
    Blog on my first and now second season of proper riding/racing - www.firstseasonracing.com
  • AnonymousAnonymous Posts: 28,799
    okgo wrote:
    Good example was a clubmate of mine who is VERY light did 5.5w/kg for 25 minutes yesterday in the National 10 mile time trial and came 50th, I did less than 5 w/kg and was 14th and it was on a rolling course too.

    What were your times? What were the times of those placed 15 to 49? The other guy could just have very poor technique or a an extremely poor TT position if he suffered that heavy a loss. .5 of a watt/kg is not that much different if the other variables work more in your favour than his.

    If a PRO cyclist is obsessed with his watts/kg then I would assume that there is something in it. Its their livelyhood at the end of the day. The examples of Cancellara Boonen or Stannard can be countered with Peter Sagan who seems to be quite successful at everything at the moment an weighs about 74 or so.
  • okgookgo Posts: 4,368
    okgo wrote:
    Good example was a clubmate of mine who is VERY light did 5.5w/kg for 25 minutes yesterday in the National 10 mile time trial and came 50th, I did less than 5 w/kg and was 14th and it was on a rolling course too.

    What were your times? What were the times of those placed 15 to 49? The other guy could just have very poor technique or a an extremely poor TT position if he suffered that heavy a loss. .5 of a watt/kg is not that much different if the other variables work more in your favour than his.

    If a PRO cyclist is obsessed with his watts/kg then I would assume that there is something in it. Its their livelyhood at the end of the day. The examples of Cancellara Boonen or Stannard can be countered with Peter Sagan who seems to be quite successful at everything at the moment an weighs about 74 or so.

    I was wrong, it was actually 23 something, but the point remains re placing. I was about 90 seconds faster. He doesn't have a poor position and 0.5 wkg for me is 40w, which is a HUGE amount and one that technique has little bearing on. The issue is that 400w that I did is going to beat 250w that he did on nearly all roads in the UK, apart from long sustained climbs, and for him, ideally the steeper the better. There are not many of those here, hence the importance of w/kg being somewhat less than someone who is constantly climbing up 30-50 min climbs like pro cyclists are.

    74kg is a lot for a pro rider, if it was really super important to him he would lean down, like Geraint does. The bulk of the peloton in classics type races (which have terrain more like the UK) likely don't care 'too much' what they weigh, rather than they're powerful. Chris Froome would not win the tour if he weighed a hand full of kg more. But for the average rider, n the uk, they'd be best eating to be lean, and training to be more powerful.
    Blog on my first and now second season of proper riding/racing - www.firstseasonracing.com
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