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Power and Speed

lbmxj560lbmxj560 Posts: 51
Hi guys

I have recently invested in a power meter that I am switching between my road and TT bike. The TT bike is a new addition this year and something I built myself. That said, it has a modern frame and I have got it setup in a relatively good position (certainly not perfect, but not bad either).

Now, I have been out for some spins just to see what kind of power I can hold in the aero position, at what heart rate and RPE. I have already worked out that I cannot quite put out the power on the TT bike that I can on the road bike, but it's not by much. Probably around 20w less at threshold (which for me is 240 - at the moment).

I am 6"1 and 72 kg. Relatively tall but pretty slim.

The other day (albeit on winter wheels) I had a laugh to see what 400+ watts would feel like. I managed about 30 seconds before I started getting a little bit short of breath :oops: . On looking at the data, I topped out at just under 30mph and this speed was pretty steady for most of the effort.

What I can't work out is this... on looking at various blogs (for example, Super Murph's excellent TT blog), it seems like people are able to avg 270 - 310 watts and crack 30 mph yet I needed to push out around 430w to not even crack 30. Hmmmmmm.

I know some of it will be down to position, wheels and clothing, but I cannot believe that would account for in excess of 100w difference.

Just wondering if anyone had any thoughts? I know it's a very open question, I just wanted to see what ppl thought about it!

Thanks all

Posts

  • slowbikeslowbike Posts: 8,490
    Which bike did you do this test on?

    The answer is, of course drag and gradient. Drag will increase with headwind too - but also from lack of overtaking traffic.
    Don't forget - power readings are a relative thing - they can vary depending on which device you're using.

    Which power meter are you using? and were you looking at averaged power?
  • Hi guys

    I have recently invested in a power meter that I am switching between my road and TT bike. The TT bike is a new addition this year and something I built myself. That said, it has a modern frame and I have got it setup in a relatively good position (certainly not perfect, but not bad either).

    Now, I have been out for some spins just to see what kind of power I can hold in the aero position, at what heart rate and RPE. I have already worked out that I cannot quite put out the power on the TT bike that I can on the road bike, but it's not by much. Probably around 20w less at threshold (which for me is 240 - at the moment).

    I am 6"1 and 72 kg. Relatively tall but pretty slim.

    The other day (albeit on winter wheels) I had a laugh to see what 400+ watts would feel like. I managed about 30 seconds before I started getting a little bit short of breath :oops: . On looking at the data, I topped out at just under 30mph and this speed was pretty steady for most of the effort.

    What I can't work out is this... on looking at various blogs (for example, Super Murph's excellent TT blog), it seems like people are able to avg 270 - 310 watts and crack 30 mph yet I needed to push out around 430w to not even crack 30. Hmmmmmm.

    I know some of it will be down to position, wheels and clothing, but I cannot believe that would account for in excess of 100w difference.

    Just wondering if anyone had any thoughts? I know it's a very open question, I just wanted to see what ppl thought about it!

    Thanks all

    Thanks for the comment. I'm not able to offer a scientific explanation for your point but essentially don't worry, it's quite normal to do 400W+ for an interval and not hit 30mph. I was doing a 30s all out sprint every 5 minutes on Friday, https://www.strava.com/activities/440182595/overview reaching over 1000W averaging maybe 500W and was only just hitting 30mph on some occasions.

    Terrain will make a big difference, aero also, but the "270-310 average" you mentioned above is over 10 miles, not a few hundred metres. Anyone who is doing 30mph (long 19) average on a 10 mile TT at that wattage is undoubtedly very aero or is on a very fast course like the V718.
  • jibberjimjibberjim Posts: 2,810
    Are you really that unfit or old? 6w/kg at a lean weight for a young man who's been cycling for a number of years is appalling. It's the sort of number anyone should just jump on a bike and do, and it should respond quickly to training. It makes me doubt your power meter. As supermurph says, because of the acceleration actual speed in an interval will not be the same as you could sustain.
    Jibbering Sports Stuff: http://jibbering.com/sports/
  • fenixfenix Posts: 5,437
    Are you really that unfit or old? 6w/kg at a lean weight for a young man who's been cycling for a number of years is appalling. It's the sort of number anyone should just jump on a bike and do, and it should respond quickly to training. It makes me doubt your power meter. As supermurph says, because of the acceleration actual speed in an interval will not be the same as you could sustain.

    That's a bit harsh isn't it ?

    And I really doubt anyone should be able to jump on a bike and do that.
  • Have a look at Best Bike Split. The models on there allow you to put in your size, weight, position etc and calculate the power needed to do a certain speed or the other way round. It can also allow for road conditions and weather etc.

    6w/kg isnt bad for 30 seconds or so.
  • jibberjimjibberjim Posts: 2,810
    6w/kg isnt bad for 30 seconds or so.

    Yes it is, 6w/kg is the typical "untrained" value for a minute, thirty seconds should be significantly higher.
    fenix wrote:
    That's a bit harsh isn't it ?

    And I really doubt anyone should be able to jump on a bike and do that.

    All evidence suggests otherwise. And my point was that it's more likely that his power meter is inaccurate, and under-reading, either just during the test or more generally, because people who are genuinely doing max efforts at 6w/kg for the 30seconds when lean like the OP, and not because they're 50kg's overweight are not really considering buying TT bikes etc.
    Jibbering Sports Stuff: http://jibbering.com/sports/
  • RChungRChung Posts: 163
    This is at steady state, ignoring acceleration. Depending on acceleration, gradient, rolling and aero drag, and wind you could need quite a bit more than this -- though the model of speed for drag is so well-understood that if you knew those things you can quite accurately determine speed. Though I'm sure there are riders who cannot do 6 watts/kg for 30 seconds, I would think it easily attainable by almost all riders whose FTP is 3.33 watts/kg (=240 watts/72 kg).

    watts-cda.png
  • NapoleonDNapoleonD Posts: 18,632
    I always chuckle when I see that graph as its so bang on (for me anyway!)
    Twitter - @NapD
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    ABCC Cycling Coach
  • giropaulgiropaul Posts: 414
    There's a danger in looking at internet forums and comparing your power with others'.

    Everyone, it seems, pushes out watts that should see them with a pro-team contract.

    In reality, things are a bit different. I help with the Maximum Minute Power (MMP) tests on the Wattbikes locally, for use in training classes there - to accurately establish zones. It's worth remembering that Wattbikes were developed with, and used by British Cycling and are much more accurate than many other measuring methods.

    Typically, with riders who are regular cyclists, triathletes and some racing cyclists, we might see figures from 200 Watts to 400. Some of the around 400+ watt riders are National standard racing cyclists.

    So don't beat yourself up over watts, people "overstate" on the web sometimes.

    As far as your road bike/tt bike go, I'd look at your position on the tt bike versus your road bike, and how your saddle/bracket/angle of leg alters if it does. It may mean that you could do with a tt bike fit, but more often it just means that the rider needs to do regular rides on the tt bike to get accustomed to the position.
  • amaferangaamaferanga Posts: 6,789
    6w/kg isnt bad for 30 seconds or so.

    Yes it is, 6w/kg is the typical "untrained" value for a minute, thirty seconds should be significantly higher.

    6W/kg MAXIMAL 30s effort is pretty poor, but did the OP say it was maximal? He does say he got a bit short of breath after 30s, but that in no way suggests maximal to me.
    More problems but still living....
  • I know some of it will be down to position, wheels and clothing, but I cannot believe that would account for in excess of 100w difference.

    There are many factors that can explain the power difference at same speed. If we assume your power meter and speed is correct, then there are many things things that can cost ~ 100W at approx 40km/h (25mph). Three of those include wind, the gradient and your coefficient of aerodynamic drag and frontal area.

    Headwind increase from 0km/h to ~7km/h:
    power%20impact%20of%20wind_zpsv1ytkp2j.jpg

    Gradient increase from 0% to 1%
    power%20impact%20of%20gradient_zpsxjlib1vk.jpg

    Coefficient of Drag Area increase from 0.28m^2 to 0.39m^2:
    power%20impact%20of%20CdA_zpslje7ymmw.jpg

    Or a small barely noticeable contributions from each of these factors combined:
    power%20impact%20of%20gradient%20%20wind%20%20CdA_zpse1bclzjx.jpg

    Another is an acceleration. Over 30 seconds, 100W is required to increase kinetic energy of an 82kg mass by 13km.h from ~30km/h to ~43km/h, or by 10.5km/h from 40km/h to 50.5km/h.

    So one needs to factor in any differences in starting and ending kinetic energy as well.
  • Hi all

    Thanks for the (mostly) constructive feedback.

    I was just curious more than anything. The power meter is a stages power meter. I have no concerns about its accuracy (or about the left/right balance - i have been on a watt bike and it stays pretty much 50/50 at various power levels). And, just to clarify, that was not my max 30sec effort, it was hard, but not max. Yes, 3.3 watts per kilo means that I am not fast... guess what, that's why I am training. It must be really nice to push out 6 watts per kilo in an ivory tower.

    Anyway, back to question at hand... those graphs are very useful indeed. The morning was cold, it certainly wasn't a still day (pretty windy, in fact), I was wearing winter clothes and neoprene overshoes, a standard helmet and was using very basic wheels with cheap tyres. Looking at all of this I suspect that I was "bleeding" a lot of wattage via these various parts.

    And yes, Nap, I definitely need a fitting. I saw in your post that you had gained 40w at threshold after a fitting with Adrian, so that is something I am going to invest in.

    Long term, it would be nice if I could boost my wattage to c. 4 watt per kilo at threshold. I just wanted to make sure that I wasn't doing something drastically wrong when I appeared to be having to push out serious wattage to not go particularly fast!

    Thanks again all
  • cougiecougie Posts: 22,512
    Sooo sorry to be dumb but would my trainerroad 30s record not be the same as my maximal 30s power?

    I've been riding for years and I'm not hitting 6w/kg there?
  • Sooo sorry to be dumb but would my trainerroad 30s record not be the same as my maximal 30s power?

    I've been riding for years and I'm not hitting 6w/kg there?

    Have you ever done an all out 30 second effort on trainer road/turbo before? If so that is your max 30 sec power (on the turbo which will be lower than you should be able to manage on the road).
  • Sooo sorry to be dumb but would my trainerroad 30s record not be the same as my maximal 30s power?

    I've been riding for years and I'm not hitting 6w/kg there?

    There's a good chance your TR 30s record is not the same as your maximal effort; it depends entirely on the workouts you've been doing on TR. There certainly aren't a lot that include an all-out 30 second sprint.
  • fenixfenix Posts: 5,437
    My plans are for 25m TTing - so sprinting speed isn't an out and out priority for me.

    That said - there are some sessions with flat out 30 second sprints - and I do 2 spin classes a week that have 20s to 30s sprints.

    I'm not hitting 6w/Kg :-(
  • AK_jnrAK_jnr Posts: 717
    edited December 2015
    It cant be right, are you using a PM or virtual power? For example I hit 10w/kg for 30 seconds during a 1 minute effort to breakaway for the win in a 3rd cat race. The 1 min power was 8.5w/kg which look at the rough guide on this chart is nothing special.
  • RChungRChung Posts: 163
    My plans are for 25m TTing - so sprinting speed isn't an out and out priority for me.

    That said - there are some sessions with flat out 30 second sprints - and I do 2 spin classes a week that have 20s to 30s sprints.

    I'm not hitting 6w/Kg :-(
    Sigh. I'll be 62 years old later this week, I haven't ridden the bike much over the last three months, my FTP in watts/kg is lower than the OP's, my kg is higher than it should be, I've never in my life won a race (except for the race to avoid finishing DFL), I've had no illusions that I've been anything but slow all my life, and last week I put out 6 watts/kg for 45 seconds. And that was just an effort needed to hit the traffic light on my commute to work. (Yes, at the moment I'm commuting on a bike with a power meter; that's unusual but luckily for this conversation I happen to have the data). I think I could've done more but once I knew I could hit the light I backed off a bit. I'm embarrassed to admit to such meager output.

    6 watts/kg for 30 seconds ain't the same thing as 6 watts/kg at FTP. If your FTP is 3.3 watts/kg, 6 watts/kg for 30 seconds isn't that hard.

    But then I don't do spin classes. I ride on the road. Maybe that makes a difference.
  • amaferangaamaferanga Posts: 6,789
    Turbo trainers have their uses, but they're definitely not for short duration maximal efforts. Any number on the turbo is likely to be well below true max power.
    More problems but still living....
  • Just to mention that you can find out approx power / speed combinations on local routes using strava. Also on a personal note I am about your weight and not dissimilar FTP. I can hold 400w for only about a minute and achieve about 40kph at 1% uphill and 50kph on the level. 50mph = 30mph so thats almost exactly what you found. When trying to go fast outside wait for a v calm, warm day those are optimum conditions (unless you are trying to be wind assisted).
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