Race predictor not updating despite significantly better performance recoded with same device

Very strange that it would under predict... usually garmin is super aggressive on stuff it seems to me.  Like for me, ran a marathon last April predicted 20sec per mile faster than I did (it was a PR and super happy with the effort).  

I never knew this graph existed, thanks!

According to the help '?' at the top right, it is using your training history as well as your VO2max to come up with the graph.  So for me it seem to jive with that.  Has your vo2max went up with your training?  To get that accurate you need to have your maximum HR set properly (not estimated or auto!)  You will want to do a test (google max HR interval test) to figure it out, or a very hard finish warm-weather 5k... then maybe add a few bpm.  Can look at very hard past workouts to double check as well.  Remember max isn't max during a workout... it is MAX POSSIBLE during a maximum race effort with adreneline etc, can be much higher then a 'hard workout'.  
For instance for me if I do 4-5x hard 3minute intervals... maybe I hit 183bpm at the end of last interval.  In my PR 5k in the heat, I hit 180bpm just a 1/3rd in and 194 at the end surge!  So unless you are doubled over almost falling down... add 3-5 bpm at least.

IF your max HR in garmin is too low. (or weight much higher)... it thinks you are working very hard to maintain your pace.  Which then will give you a lower then actual vo2max... and slower pace predictions.

ALSO:  If using optical HR, often this can be inaccurate or hit or miss for acccuracy  (mine is horrible for it, wife/friends have great results most of the time).  A HRM strap like Garmin HRM-Dual or Polar HR etc is recommended if wanting to get the most out of the Training Load, Fitness, Recovery, etc data information.  One bad HR reading run (easy run at 95% HR!!?!?) can screw up the entire week/month of Vo2max data and shift training load to very high vs low!

I have the same problem. My personal feeling is it's based mostly of VO2 scores, but that doesn't count for running economy. Having had it measured in a lab my VO2 estimate is pretty accurate (and lower than it used to be which is a shame.) But my running economy has improved a lot over the last couple of years. as my VO2 has declined the race predictor times have also, but despite that I can outperform my Garmin estimates. It's annoying, but not sure we can do much about it so I've turned the widget off now.

Yeah there is a lot that goes into race results... vo2max is NOT a gauge of aerobic fitness and is a genetic component for a large chunk....  but things like economy, efficiency, lactate threshold and many other things come into play.  You can plateau your vo2max, but build much more mitochondria with lots of easy volume and do lots of lactate threshold workouts, leg strenth lifting, plenty of strides... and get better race times! 

For instance I have trained hard and ran a few marathons in of 3:03 from 2018-2021... Looking at history all with varying vo2max values (59~61).   So clearly not the only component to endurance aerobic sports!

However... 
Broke the streak of 303 with PR 2:59  w/63~64ish , so who knows LOL

Thanks Karlos. I get to the same conclusion. Better turn it off when it is becoming a nuisance or distraction rather than a useful training/planning tool. Disappointing with regards to the device/software/data capabilities though.

The Race Predictor is also significantly based on training load... so you can use it as a relative metric for improvements, also it might use more detailed vo2max readings then whole number.  So it might be using small changes 55.2... now 55.6  etc.   Also it looks at type of training it seems, because in December it says my 5k time is the fastest of late... but that same month was my slowest predicted Marathon pace (likely due to total volume and length of long runs?)

Although I do find the Training Status page to be the most helpful for monitoring long term improvement (even with a flat vo2max value)... my vo2max was still high after recovering from Boston marathon injury in April... but was still biking & hiking a lot.  So slowly my Marathon "predicted pace" has come back up now that I am doing 15-18mi long runs again.

Hey man, since the 12.1 was release i can see vo2max, training status and result predictor are not working as they should. Today I just ran 4k at 3:59 ((inside a longer session) and the race predictor still gives me 20:25 on the 5k as it did yesterday. Also, last year I was at this same level of training and my vo2màx was showing st 54 i believe. Instead, despite having the very same results (time and BPM wise), as of now it is stuck at 51 since forever. I believe we need to wait for Garmin to release che 12.51 update. I read somewhere it would fix these issues.