Virtual power on a Turbo - how realistic?

mickisup
mickisup Posts: 295
edited November 2014 in Training, fitness and health
How accurate is Virtual Power on the KK Road Machine? I ask as although I think the 1 minute, 5 minute and FTP values I am getting as are fairly accurate and realistic, I am finding the 5 seconds max power figure targets impossible to achieve.

As I have never used a power meter on a bike outside I have no idea whether my very poor watts/kg figure for a sprint is indicative.

The turbo when setup correctly is harder surely than a flat section of road when attempting max effort?

Comments

  • davidof
    davidof Posts: 3,115
    Watts is watts. 1000 watts on the road is the same as 1000 watts on the turbo for a given cadence (at least using a power meter).

    However with VP you are measuring power at the back wheel based on the speed you can turn a flywheel against how much you can bend a bit of metal (pedal, crank arm) so there is going to be a good deal of inertia on the turbo which will be reflected in VP measurements.
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  • bolingbroke
    bolingbroke Posts: 32
    It's entirely possible that you could just have a poor sprint that you need to work on. I have found virtual power can be off by a fair bit to actual power but I've always trusted it to be calibrated so it is consistent. i.e. if my actual; power is 220 and TR shows me 200, it will also show me 500 when I'm actually at 520.
  • jgsi
    jgsi Posts: 5,062
    bolingbroke wrote:
    It's entirely possible that you could just have a poor sprint that you need to work on. I have found virtual power can be off by a fair bit to actual power but I've always trusted it to be calibrated so it is consistent. i.e. if my actual; power is 220 and TR shows me 200, it will also show me 500 when I'm actually at 520.

    Thats a pretty good proximate guestimate on the part of Trainer Road and the virtual power profiles it uses.
    A range of 10 to 4 % being off difference is actually no deal breaker in general terms of the normal Bike Radar person who is training for a bit of amateur sport.
    I really dont think many pro or semi pro riders have to rely on virtual power in this day and age.
    If ever I receive my Vectors, I'll be doing the same of checking what the difference is.
  • Grifteruk
    Grifteruk Posts: 244
    A couple of months ago I repeatedly tested my KK Rock n Roll with the Kinetic inride power output against my Stages powermeter by riding both on the turbo at the same time (and no my carbon frame didn't break on the turbo :D ).

    I did not go for any max power outputs as I don't tend to use the turbo for max sprint efforts (I am training for the Haute Route 2015 so plenty of base at the moment with longer sustained efforts in the new year). However over a range of power zones up to around 650watts readings came out pretty close to each other (within 10 watts over the hour session and on shorter intervals) to the point where I was comfortable I was within the same training zones on both the road and turbo. Agreed that the readings are from different places (wheel or crank in this case) and the results were not perfectly symmetrical, but good enough for me. Worth checking out the DC Rainmaker site, who some time ago tested the KK inride against other powermeters and found it comparable in many respects. Google it and you will find it I am sure.

    That is not to say that for me the turbo does not feel different to the road, but not sure if that is the question you are asking. Personally I have always found it much harder to replicate sprint/max efforts on the turbo for very short durations. By way of example on the weekend without really paying attention to output I put out 998 watts on the road bike, but whilst I have not tried in many months I suspect doing that on the turbo would be a different prospect entirely.
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  • mickisup
    mickisup Posts: 295
    (Interesting reply from Grifteruk above)

    Without wishing to start a competition I would be interested in what max 5 seconds power others are getting.

    On the Turbo I can just about sustain around 500 for 5 seconds which gives me a maximal power output of just 5.88 w/kg.... :oops:

    According to my power meter book World Class sprinters can push out 25.18 w/kg, which means they are pushing upwards of 2100 Watts for the same time interval.

    I am convinced I can could get more than 500W on the road, just wondering whether others find it easier to get better figures on the road or whether its just as suggest my bad sprinting!

    I am fairly fit and my FTP is not as bad.
  • bigmat
    bigmat Posts: 5,134
    My peak power on the Wattbike is around 1700W, not sure re 5 second power but I would guess around 1200W? Never used a power meter on the road but fairly sure my readings would be lower, I personally find it easier to get my head down and power away to exhaustion on the Wattbike whereas I always seem unable to "jump" in an actual sprint, probably due to crap reactions, tiredness etc.

    FTP is around 340W for reference.

    Hoping to get hooked up with trainerroad this winter so will be able to compare power outputs on there and hopefully confirm the Wattbike is in the right ballpark.
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  • mickisup
    mickisup Posts: 295
    We have a couple of Watt Bikes in work gym so maybe worth using that as a comparison, thanks for the idea.
  • jgsi
    jgsi Posts: 5,062
    3.jpg power numbers from a pro rider
    I do believe that Andre actually did a dyno test in the lab last year and pushed out 1400 watts... so take from that some comfort ;-)
    Personally I'd be more interested in matching his 225 watts for 100 miles...
  • Alex_Simmons/RST
    Alex_Simmons/RST Posts: 4,161
    To generate maximal power, you need a sufficient resistance load when accelerating which most home indoor trainers lack.

    Trainers like the KK don't have anywhere near the inertial load that a bike rider riding outdoors has. It requires a large and very heavy flywheel with double reduction gearing to get close to the sort of inertial load of a bike rider. Plus tyre slip can be a problem.

    Apart from that I'm not sure the models used by these systems account for changes in kinetic energy, are they not simply reading from a curve that matches speed with power? these are for steady state power only and not realistic when any form of acceleration is happening.

    IMO it's pointless to consider such trainers for neuromuscular power development or such virtual models for peak power measurement.

    As for Greipel, I'm sure that when fresh his peak power is much higher, but even so he's an endurance rider, not a sprinter which is what the power profiling tables for 5 second power are based on. Indeed I suspect the highest peak power is from a BMX rider now and not a track sprinter. Their peak power abilities are very similar and far higher than pro roadie "sprinters".
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