Thursday, August 19, 2010

2010 Mount Tam Double Results: net time versus start time

I did some quick analysis on the relationship between the net time and the start time in the 2010 Mt Tam Double results. Unfortunately the start times of DNF's weren't provided, so all I can work with are numbers for ride finishers.

Riders were started potentially every 5 minutes. One rider, Harish Narayanaswamy, started at 6:15, 15 minutes after the official cut-off (but he still finished with daylight to spare); all others started within the official 4 am to 6 am start window. So I binned the riders by start time then did a weighted linear regression of the average net times. The result is plotted here:

Mt Tam 2010

Not surprisingly, faster riders tended to start later. Or perhaps riders who started later tended to be faster due to less riding in pre-dawn darkness, although I suspect more of the former. Obviously it takes a special motivation to get out there for a 4 am start, foregoing the advantage of the 5 am mass-start, and a nice source of such motivation is fear of riding after sunset on much more heavily trafficked roads, or fear of missing the 10:30 pm cut-off.

Note the slope is < ‒1 (value = ‒1.69, standard error = 0.21), which means riders who started later in the morning tended to finish earlier in the evening, so it isn't a simple matter of riders pushing up against sunset or the cut-off.

Interestingly only 59% of the 194 finishers started with the main 5 am group. 36% started earlier and 6% started later.

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