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TSS different PT vs Garmin 910

Michele CellaiMichele Cellai
in General Training Discussions

Yesterday for RR, I used PT and Garmin 910 during ride. 4.5 hrs on CT, 1.5 hrs outside.

When downloaded, TSS on PT read 284 vs Garmin of 334. 

This is a huge difference.

However... I trust the PT, and here is why.

The PT is reading my distance off the spinning wheel, while the Garmin is trying to do it by satellite. Obviously this is useless during the 4.5 hrs I am inside.

If you look at the 1.5 hrs I was outside, the TSS are close: 69 by Garmin, 71 by PT.

Next ride I will try to be outside the entire time and compare. But this is interesting.

Comments

  • jhbinscjhbinsc

    I haven't used my 910 for TSS calculation as I trust my SRM however my SRM PC7 and 910 agree within 1 watt for AVP on numerous outdoor rides. I have noticed that occasionally the 910 needs to be calibrated as for some unkmown reason the offset will drift, sometimes dramatically. Have you calibrated 910 or did you before this ride?

  • tuckermtuckerm
    I can't help with the difference here but am wondering why would the 910 be using a satellite to calculate TSS? It's a mathematical formula. I get that the distance would be wrong if your 910 was using satellites for that, (can you turn off that satellites?), but there is no distance input the TSS formula.
    Also, you say you trust the PT. I assume Powertap? What were you using to get the TSS from the PT?
  • Michele CellaiMichele Cellai
    All downloaded to WKO.

    Satellites for distance on 910. Didn't think about turning them off as I use PT for distance.

    I haven't calibrated 910, but the watts match PT exactly. It seems that when on the trainer, the 910 thinks I am working very hard to go not very far.

    Perhaps I misunderstand calculation of TSS. But if they are identical for outside ride, and vastly different for inside, I feel like the distance must have something to do with it.
  • tuckermtuckerm
    TSS = [(s x NP x IF) / (FTP x 3,600)] x 100 Zero distance component.
    Honestly I have no idea why it isn't working.
    But another question, how is the 910 giving you TSS? I thought that firmware had not been updated yet?
    And I only suggested turning the satellites off while inside because this is what many will do when running on a treadmill with a footpod.
  • Michele CellaiMichele Cellai
    I get the TSS from the 910 only on download to WKO+.

    WKO+ is calculating TSS on PT and 910.

    I started to type- "Now I really have no idea why they are so different." Then it occurred to me- I used the 910 in multisport mode.

    I went back and checked WKO+.

    On the download it gives me a TSS for the "bike", but with a time equal to the entire bike/ run. If I select just the bike portion, the TSS was almost identical between PT and 910.
    PT = 284
    910= 281

    It is deceptive because it does give you a separate run TSS.

    This is another 910 flaw, IMO.
  • jhbinscjhbinsc

     I'm also curious how you re getting TSS from 910. Are you running both PM and 910 data through wko?

  • jhbinscjhbinsc

     I just saw this post. Now that makes more sense. And yes, I agree it is yet another 910 flaw! Garmin needs to get their act together better.

  • [Deleted User][Deleted User]
    Interesting. I think I'll avoid the multisport option. I don't think you can use the lap button within a sport when in multisport mode either, other than to change from one sport to another. I'm sure I'd mess that up in a race. I must say that overall I am really liking the 910xt. I am a little concerned about it popping out of the quick release thing during the swim though.
  • Michele CellaiMichele Cellai
    Jim- You're right, you can't use the lap button, but you can use auto lap. I still get 1 mile splits for the run and I'll use something for the bike.
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