I just ran a 20:30 5k and my race predictor show's over 24 minutes. It's only been a week since I started using it, hopefully it'll get better with more data.
Did it get better? I have mine for a month now and it actually got worse... 1:30off at 5k, 5min off at 10k and 15min off at half
Mine is much more accurate than on my old 235. Did a 10K on Sunday and got within 10 seconds of projected time. New 10K time is about 50 seconds faster than PR but HR time is about a min slower than my PR!
Is it very hot and or humid where you are now? Is your training volume much different to when you set your PRs? Any other factors you could think of?