Garmin predicts 17:16 5k and 36:04 10k after running 34:12 10k. Why?

It averages the last few (?) running sessions, so that would include pre-race sessions (which you may have been taking easy.)

Regarding its predictions, you should be seeing how they line up with a reliable calculator, like the Jack Daniels calculator. The Tanda Calculator may also be of interest; it projects marathon time based on: (1) weekly volume, and (2) average pace of weekly volume.

Also, you may need to modify the Max HR setting to a more accurate value, and optical HR measurements (from the wrist/watch sensor) can be inaccurate; a HR strap is recommended for more accurate HR measurements.

Garmin has been telling me for years that my threshold pace is 30+ seconds per km slower than my half marathon time. But strangely, it has been pretty accurate at predicting my 10k to half races.

The race predictor is based on the Vo2 max value garmin estimates when you run with a heart rate monitor. That VO2 max value will drop off it is hot/humid or you are running on hilly terrain. Basically anything that would make you heart rate higher for a similar performance. I wouldn't put too much faith in those predictions.

I have the opposite problem.

I'm 65 and Garmin predicts a 17:42 5k - age graded 13:48 and 37:42 10k - 29:18, and that's after racing a 3000m in 11:33 and a 20:08 road 5k.

It's based on HR and percentage of max used at various speeds, I'm going to guess it just took your race as an outlier, so it just improved your average.

Mine numbers are messed up as I can run reasonable fast at a low percentage of HR (probably the result of 50+ years training), but at this stage don't have the legs to push up to max for any length of time.

I never understood this either. If the Garmin watch thinks you can run a 38 min 10k, but then you run a 36:30 10k, the prediction should actually adjust to your recent times you have run. It's so dumb.

You have a very truthful Garmin and it is telling you your 34:12 10k was only an 8k. With this being said I'd stop telling chic's that your rocking 6 inches of man hood because it's probably only 3.5.

To answer your second question; obviously not.

Is English your first language?

One very significant finding of mine, which I have yet to see mentioned on this board, is that the Garmin Race Predictor and Garmin VO2max Prediction can quite easily be ‘fooled’ into inaccuracy; and if one is not aware of this issue, they may not realize how they are not purposely affecting Garmin’s predictions

Before I share this finding (if I actually do choose to share it here), I wish all to see what type of evil and downright stupid mentality inhabits this board. You see, in my previous posts above, I gave you good and accurate information, and yet, the posts were downvoted. That is evidence of what I’m referring to.

Nice time king/queen

The reason for this is that the Garmin prediction data is shaky, at best. It's as simple as that.

I take it you are some low income moron based on your snappy come back!

Garmin thinks I can run a 19:xx 5K. I think it's even predicted high 18s. My actual recent PR is 21:xx, and I've been running 30 years, so I'm pretty confident in what I can and cannot do. Basically, in my opinion, Garmin's predictions are completely worthless, and I suggest ignoring them.

It depends how it is used, because that can affect the results.

I am a 21 year old college running with a 5k pr in the low 14's. My garmin race predictor has never gone under 16 minutes for 5k or 35 minutes for 10k. The only time I don't wear it is when I charge it. All the data is useless except for measuring distance of a run

The algorithm sucks, it's as simple as that.

I ran a half marathon recently in about 1:20, the watch still tells me my lactate threshold pace is 6:27/mile, which is about 30s/mile slower than my half marathon race pace.

You probably do not have the correct max HR stored in the watch.

Considering the advanced state of AI these days, you'd think Garmin would be able to do better. Their 'performance condition' alert seems largely a waste of time as well.