Continuing to have issues with PT on trainer

Discussion in 'Power Training' started by bgoetz, Jan 3, 2013.

  1. bgoetz

    bgoetz Member

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    Ok, I have posted regarding issues with my PT on a trainer before, I really thought replacing the bearings corrected my issues, but after today I don't think it did. I have always figured my power to be lower inside, so only gave a little thought to lower numbers, but what I notice with my 3 second power readout does not seem right. It seems if I am not near my max output and my pedal stroke is smooth (i.e the majority of the time) everything is fine and power readings look consistent. When things get strange is when I start to get fatigued and my pedal stroke is not as smooth or I lower my cadence the power readout from my 3 sec average goes nuts, one moment it reads 340, the next 260, as it does this it works its way to the low end to the point where I know I am going harder then I was previous yet the power displayed is lower. It really seems to me that the PT on the trainer somehow over compensates dead spots in my pedal stroke. I have also gone back and forth about if it matters when I zero my Garmin should I do it with roller pressure on the rear wheel or off? Anyone have any experiences similar?
     
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  2. Freddy Merxury

    Freddy Merxury New Member

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    Is it possible you are getting rear wheel slippage at the lower rpm and higher torque? That would explain the fluctuations in power and jerkiness.
     
  3. RapDaddyo

    RapDaddyo Active Member

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    What does the raw data look like? The PT precession effect causes some of the variability in the power observations even if your cadence and power output are absolutely constant. I don't know if the precession effect would cause such a large variance, but it is significant due to the fact that virtually all of the power per stroke occurs in two short arc segments. FWIW, I normally set up my handlebar computer with 5sec averaging for watts.
     
  4. daveryanwyoming

    daveryanwyoming Well-Known Member

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    That sounds like some form of sampling artifact. When you look at the data in WKO+ what does it look like with no smoothing vs say 10 second or longer smoothing applied? The PT uses time sampling in units of a second or more depending on the vintage of your PT hub. If you're pedaling less than 60 rpm then you won't complete a full revolution per sample which can lead to strange aliasing artifacts. You wouldn't expect to see those with 3 second display smoothing but perhaps if they're very pronounced or the aliased components peak at a multi-second rate you might see something like you're describing.

    The other thing to check is a pair of static torque (aka stomp) tests, one with the bike out of the trainer and one with the bike mounted in the trainer to see if the torque tube is being loaded unusually and changing readings when clamped into the trainer. That shouldn't change as much as you say, but perhaps there's something else happening at lower, less smooth, cadences. IOW, you could be rocking the bike more at those times and if there's an interaction between your trainer clamps and your torque readings that could introduce some variability.

    -Dave
     
  5. bgoetz

    bgoetz Member

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    I lowered the pressure and tightened it more than normal today. I didn't hear it slipping, although today seemed to be the worse yet. My 1st 15 min I started at 340ish, I wanted to target 330 so I actually backed off a bit. I was watching my computrainer readout for pacing as I try to look ahead and targeting 298 seemed to keep me around 330 as I don't ever bother calibrating the computrainer. The second interval again 330 target, I held 300-310 on the computrainer not even looking at my true power until 5 min to go and to my surprise it was 310. The thing is it was the same effort as previous HR and PE. Once I noticed I was low I tried to up it a bit and at that point noticed just how erratic my readout was. My PE, HR, and looking at what should have been a consistent # on a warmed computrainer all lead me to my conclusion that something is not right.
     
  6. bgoetz

    bgoetz Member

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    Dave, if I look in WKO I can visually see where thing get erratic on my power graph followed by a slow downward trend in power. I have stomp tested out of the trainer maybe I will try it in the trainer. It is so frustrating because it seems more pronounced when I am suffering the most, but I have watched my power before outdoors when I am hurting and it never does this
     
  7. bgoetz

    bgoetz Member

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    As far as calibrating my Garmin with the roller clamped vs not clamped would that make a difference?
     
  8. daveryanwyoming

    daveryanwyoming Well-Known Member

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    It shouldn't, but it would be another interesting test to see if you can introduce static calibration differences in or out of the trainer.


    Some or all of that could be due to inertial differences indoors vs. outdoors. Are you running the CT in ergo mode or programmed resistance (course profiles) mode? In erg mode especially you're rewarded inertially for keeping wheel speeds high and as wheel speed drops (e.g. same gearing but getting tired and producing less power or downshifting hoping to ease things up as we get tired) the effort level can skyrocket as we lose a bit of power but give away wheel speed which costs us precious inertia and turns a mid to high cadence effort into a pulsing slog.

    The insidious thing is that it's hard to climb out of since we'd need more wheel speed to regain the inertia but now the erg unit has bumped up the braking resistance and it doesn't react immediately to changes in speed so we've got to punch out even more watts at a time when we're tired to try to 'make it easier'. I often struggled with this during hard erg mode intervals on the CT as I got tired and tried to stay on top of the power. Maybe what you're experiencing is very different but I didn't realize you were talking about a CT and if you're also talking about erg mode then it triggers some memories of similar things.

    -Dave
     
  9. daveryanwyoming

    daveryanwyoming Well-Known Member

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    P.S. I'd also add that at the kind of power you're sustaining in these intervals, cooling the CT load unit is a very good idea. Sustained work in the 350 watt range, especially if you let your wheel speed fall translates to a lot of heating in the CT load unit and that could be causing some additional trouble in terms of the effort not feeling smooth and having a jerky feel along with power spikes and dips. Strong folks like you often point a small secondary fan at their CT load unit to help with its cooling.
     
  10. bgoetz

    bgoetz Member

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    Ahhhh! I think you have it Dave!! I have been doing all of my testing and hard intervals on spin scan @ 1%, as opposed to a flat course. Now that you mention it my best efforts have all been on a course. Hell I did an effort at the end of a 13 mile L2 that was 5min @400 and I was pretty deep into my training week. It was hard, but I felt I could have gone 20 watts deeper easy. I tested my 5 min in spin scan when I should have been far more fresh and only got 390!
     
  11. bgoetz

    bgoetz Member

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    The more I research though the more I am thinking Spin Scan should be the same as course, so maybe that is not the issue. But your description is spot on and spin scan does seem to "feel" somewhat different. BTW, I have the old NES version if that matters.
     
  12. Alex Simmons

    Alex Simmons Member

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    It is, and changing the gradient on your course to 1% simulated gradient will probably replicate that feel.
     
  13. Alex Simmons

    Alex Simmons Member

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    and just to check on aliasing effects as mentioned earlier - what cadence are you doing these efforts at?
    and what model of PT?

    newer model PTs will readily see aliasing effects at 95-105 rpm and 75-85 rpm
     
  14. bgoetz

    bgoetz Member

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    The PT I am using is the Pro+. I typically start my intervals at 90ish, but tend to drop cadence as I fatigue. I will have to check to get an exact figure, but I am thinking I was down around 83 when I was having issues. Something is going on during my MP efforts on the trainer beyond normal indoor effects, I just wish I could figure it out.
     
  15. bgoetz

    bgoetz Member

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    Well cooled the CT, confirmed that the torque is the same regardless of clamped or not, reset the roller tension, switched to a course the second effort, and even calibrated between 15 min efforts and no luck :(. It gets awful the worse my pedal stroke gets, it actually went clear down to 0 watts at one point. My two efforts were within 10 watts and truthfully my second was not as good of an effort as my first, but it has to be effecting my AP. I guess if it acts up outside maybe it is the PT. Update: after actually looking at the files I had multiple zero readings both this a.m and p.m. The strange thing is I am losing everything, speed, cadence, and power for about 3 seconds. It also seems to be happening when I am not going hard. It is certainly having an impact on AP, and looking back seems to have just started today. So, I may have corrected the previous issue with the bearings and this may be a whole new problem that just started.
     
  16. RapDaddyo

    RapDaddyo Active Member

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    This sounds like either bad batteries (hub or handlebar computer) or your hub needs service. You should not be getting data drop-outs.
     
  17. Alex Simmons

    Alex Simmons Member

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  18. bgoetz

    bgoetz Member

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    I am losing everything though and my Garmin shows 100% :(. I have not looked to see if it dropped anything this a.m., maybe it was some type of interference that just happened yesterday. If it keeps dropping things I may reinstall the software or do a hard reset, I sure hope it is not broken.
     
  19. frost

    frost New Member

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    Check/replace the hub batteries.
     
  20. bgoetz

    bgoetz Member

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    Might as well just replace the batteries, they are cheap. I just looked though and I only have 100 hours since the last change, so much for the claimed 400.
     
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