Why is the race forecast on Runalyze more accurate than on Garmin?

I've always found that VO2 max on Garmin is overestimated, thus impacting the race predictions.

I trust Runalyze, useful and accurate.

Runalyze also has a VO2 Max correction factor based on any runs you tag as races (in runalyze), which makes it even better. (So if you run 10% faster than runalyze’s prediction, for example, future VO2 Max estimation / race predictions will be 10% higher/faster)

You can add the “VO2 Max (from file)” activity column to runalyze so you can compare Garmin’s and runalyze’s VO2 Max values. (The only thing to keep in mind is that the Garmin number is a rolling average but the runalyze number is per-activity.) 

Garmin’s VO2 Max still seems pretty precise, if not accurate, meaning that it’s fairly useful for tracking fitness trends.

Are you on 12.27? This made changes to the Garmin predictions, and in my case made them more realistic

For years Runalyze has synchronized with Garmin to obtain information on the activities that I carry out with the different Garmin heart rate monitors that I have used. (230, 645, 745, 955).

So, same data, with parameters adjusted in Runalyze to match those in Garmin (baseline heart rate, maximum heart rate, and zones based on lactate threshold, age, etc.)
But very different results:
VO2max on Runalyze 36
VO2max on Garmin 51

The difference between Runalyze and Garmin was already produced with the previous heart rate monitors, both in VO2max and in race prediction.

I'm at 12.27

FYI, My RA is 54 vs Garmin 62, but in recent activities they are closer on same (59 vs 61 - a GC tempo effort ) and others not so ,much (54 vs 61 - a GC threshold effort) so it seems RA is much more sensitive 

S.M.R. said:

FYI, My RA is 54 vs Garmin 62, but in recent activities they are closer on same (59 vs 61 - a GC tempo effort ) and others not so ,much (54 vs 61 - a GC threshold effort) so it seems RA is much more sensitive 

As mentioned above, runalyze's VO2 Max is per-activity, whereas the VO2 Max that Garmin shows you is a rolling average (even the one that's recorded in the FIT file). You never see the per-activity Garmin VO2 Max.

That's why runalyze's VO2 Max is a lot more variable than Garmin's.

My RA VO2 Max is usually 10 points below my Garmin VO2 Max, although the gap is bigger when I'm out of shape, and smaller when I'm in the better shape.

In my case, I am referring to the average VO2max in Runalyze.
In fact, the variation of the average between races is minimal, (hundredths).
At the end of the day, the comparison is between the Runalyze average and the one offered by Garmin.

LaudelinoQ said:

In my case, I am referring to the average VO2max in Runalyze.
In fact, the variation of the average between races is minimal, (hundredths).
At the end of the day, the comparison is between the Runalyze average and the one offered by Garmin.

Sure, but I think the person I was responding was referring to the per-activity runalyze VO2 Max. Otherwise I would never expect to see such a huge swing (59 to 54) in a short period of time.

It is nice to see the per-activity value in runalyze, as you can really see where you're under/over performing. Like if you run a good race, the per-activity VO2 Max is usually a few points higher, but if you do a training run when you're tired or injured the per-activity value can be a lot lower than average.

Garmin is more accurate than Runalyze for me (especially after the latest fix).

I sometimes run with my kids, which tanks my VO2Max to silly levels in Runalyze, and drops my race predictions to speeds I could do running backwards. Garmin has no problems like this.

Even when I wasn't doing slower runs like that, Runalyze was like AN HOUR too pessimistic about my Marathon times. It vastly overrates running volume for that prediction if you crosstrain.

Yeah, one problem with the runalyze VO2 Max estimator is I don't think it has the Garmin/FirstBeat "secret sauce" where irrelevant data is excluded - like when you're standing still at a red light or recovering during a workout.

Like when I run interval workouts, I always record rest/recovery periods, so my runalyze VO2 Max for that single activity always ends up being extremely low. Since my workouts (not including warmup/cooldown) are usually like 10-15% of my overall weekly volume, it probably doesn't have a huge effect on the big picture, but I can see it being a problem if a big proportion of my runs were "undervalued" by runalyze.

Runalyze is always more accurate for me than Garmin (although the latest Garmin race predictor algorithms are way more down-to-earth than they were on older devices, for me). I like to tell myself it's bc I never run to my potential haha.