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7th October: 10K in 36:15
10th October: 5K in 17:04
prediction was 17:23 based on 10k time
21st October: Half Marathon
prediction on 5K time - 1:18:25
prediction on 10K time - 1:19:54
My Half PB is 1:25 and will be aiming to run 6 minute miles which would give me a time of 1:18:36. I think the calculator is pretty accurate but is clearly dependant on the training you have done, how recent your race time is and your tactics for the race. I ran the 10K conservatively to ensure my target time was achieved. I guess I could have pushed it harder.
Will see how it goes on Sunday
The real difficulties with these tools relate to marathon time predictions, especially if you are trying to predict up from a race distance that's more than 50% shorter. Most people under prepare, that's true. They also run fewer marathons than shorter races, because of the ease of recovery. Therefore the pb at the short race is when you are at peak with conditions perfect, yet the day of your (annual?) marathon could be anything but. The result being that the marathon prediction is likely to be the BEST that you could expect, and the likely spread being quite wide beneath that.
I fear also that the formula is probably in need of a minor age factor too, as several of us vet types have found that we need to be able to run a faster HM to get to a given marathon time. And that's taking the training variation into account.
for a 3 hour marathon, it suggests 1:26:20 is enough. Tosh.
Greg Macmillan reckons a 1:25 is needed, and he's a bit hopeful too. Maybe OK for a 23 year old, but it can be done off that time.
I reckon that I need to have clocked 1:23, AND put 8 runs over 20 miles in, AND that a few of those need to be fairly quick. Doing 60mpw plus is also pretty much an essential.
I know someone who is hoping to run a sub 3 off an undulating 1:24 half. For me, esp as a larger bloke, I find the longer the race the more my fade so it works for 5k/10k but not too well for maras.
There was a thread on this a while back where people collated their experiences and it turned out from what I can recall that the faster runner you were, the more likely it was to be right.
I'm now hoping I can convert this into a sub 2:45 marathon at FLM 08. As Blisters has said, it now comes down to specific maratho prep. The 1:19 indicates I have the pace, now I have to add the endurance to prove this calculator correct (It predicts about 2:44:45 I think)
Its not accurate for me yet. I can currently run 5k in 23:08 which predicts 48:00 ish time for 10k. But although I'm improving, I haven't quite broken the 50 min barrier and my pb stands at 50:49.
However, I'm still relatively new to running, carrying too much weight and my endurance isn't what it could be. So in a way, the race time predictor's value is in showing me what I could be capable of with more training.