Marathon times predicted by weight differential

As the Silicon Valley Marathon approaches I can't help but be anxious. A few days ago I caught a cold and have been fighting it since. I was hoping to get a 6 mile run in yesterday and just couldn't. Hacking, coughing and phlegm filled nose and throat is certainly not conducive to a good run. So in my spare time I've decided to play a numbers game and predict what my time will be on Sunday (that is if I feel up to it and the cold and cough have subsided).

I've read in several different places that for every pound of weight you run a mile 5 seconds slower. So I wanted to put this to the test. You see I have the perfect base run, my first marathon in 2006 when I signed up for and completed with zero training and weighing 212 pounds. Using that I've gone back to the other 4 road marathons and figured out what the weight difference was, and thus what my predicted time would be.

Obviously there are several factors that go in to running, anywhere from hydration, eating, weather, hills and so on, so it would be hard to use the 5 second per mile as a hard rule. That being said the predicted times did pretty good. My San Francisco and Silicon Valley from 2007 were almost dead on, and you can bet there was a +- factor of a pound or two considering my weight was taken from a different day.

My training was different in 2007 than it was in 2008. In 2007 it was all about the shorter races until the end of the year when I started running longer runs. Then in 2008 the Napa Valley Marathon I had obviously trained much better and my body was ready to run the distance and thus I was able to do much better, adding a 38 minute cushion because of my training. Cowtown was better as well, but I had stopped running and I am willing to bet that the difference from the predicted time was my muscle memory picking up where I had left off.

All I can hope is that I can run better than the 5 hour predicted time of my weight and the 5 seconds a mile per pound rule. I certainly haven't trained that well, so I can't really expect anything other than the predicted time. But seeing as how I had ran 2 weeks ago 2 half marathons at a little over 2 hours each, then I feel confident I can run between a 4:30-4:40... Here's to hoping, not only for a finish but that I will have recovered sufficiently to run at all.