Tim, Yep,I agree re the calcs actually. I did a half marathon at the beginning of the year in 1.57 whicj I was pretty pleased about as was spot on 9min mile all the way round..according to the running calcs I should be on for a 4.08 marathon...this is I guess achievable (thoretically based on my 18 miler) but there is no way that I can do a 25.21 5k. But the 10 mile time it predicts is a minute slower than I've run in non-race environment. Anyway doing GSR on Sunday so will be interesting to see how this one turns out!