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This one is pretty good.
Obviously you have to do the training and predicting a marathon off a 5k time is not a good idea
Has anyone done any research into the average difference between your training run times and race times? Or is there such variation that it's impossible to generalise?
My problem is this: I really want to believe the brianmac.co.uk calculator, which says my marathon time will be 4 hours 50 (on the basis of a 2:20 half). But I'm finding my training runs are currently a lot slower than that, for a number of reasons (I think carrying water slows me up, and there are lots of obstacles on my long runs, like gates and cattle grids.) Have others found that their actual race times are significantly better than their training times, or am I just being absurdly hopeful?
Training runs are notoriously bad for timing wrt races, your pace is always variable, you stop to cross roads, etc etc.
If you have "raced" 2:20 for a half and you have trained properly then you should be capable of sub 5hr marathon with the aim of 4' 50" .