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Race predictor broken?

3478351
over 1 year ago

Yesterday I ran a 10 k race at 45:40 and today, after a good night’s sleep, garmin 10 k race predictor says 49:35. How does thar make sense?

  • 0 over 1 year ago

    Mine was suddenly fixed. It has estimated 5K at 30-31 minutes for months, despite me regularly running significantly faster in my workouts. Then suddenly it dropped to 23-24 minutes after I had an easy 10.3K run at 60 minutes or so. The difference was that I had no warmup, cooldown or stretching included in my run. I will usually log something like 90 minutes for a 50 minute run, and that seems to confuse the watch. 

  • 0 over 1 year ago

    It’s incredible that with all the technology nowadays the left hand doesn’t talk to the right hand. 

    Same thing happened for years. Last year I ran a HM and beat the estimate by a few minutes. The watch knew I had just ran the race yet continued to show the old, slower time. 

    Garmin refuse to publicly explain why this happens. 

  • 0 11 months ago

    The only things your Foreruner 255 measures with reasonable accuracy are distance and average pace (if your GPS signal is good) and heart rate (when you run slow or wear a heart rate belt).

    All the other numbers that your Garmin spits out (VO2max, anaerobic threshold, HRV, etc.) are calculations, not measurements. Those guesstimates can be off by 10% or much more, especially if you're much faster than average. As a result, Garmin's predicted race times are usually off by many minutes.

    Nobody in my run club races the times Garmin predicts. Everyone is quite a few minutes faster or slower.

    The only thing Garmin's race predictions may be good for is to spot overall trends: are my times going up or down during a multi-week training cycle?

    And even those trends can be highly misleading, so don't believe your Garmin when it calls your pre-marathon tapering "detraining" or "unproductive."

  • 0 11 months ago

    I see this quite a lot, an immediate change following a workout which then adjusts overnight.

    I suspect it does a rough, local calculation at the time and during the night its a server side calculation and push so its different in the morning.

    Warmup/Cooldown and cardiac drift seem to have large effects on my predictions too.