Thursday, January 29, 2015

San Bruno Hillclimb: pace comparison 2014 vs 2015

Follow-up to San Bruno Hillclimb report:

I plot here my relative time to distance for 2015 versus 2014. To generate this plot I exploited the fact I'd hit the lap while waiting on the start line each time. When I check the profiles starting from the lap starts they are essentially the same within approximately 20 meters of distance. However, if I were to have started the times at the start of the lap, the times would have been dominated by the delay until the race start in each case. So instead I interpolated the starts from 20 minutes after the actual lap start.

To match times at distance, I interpolated times onto 20 meter intervals for each year's data. Since the course is close to 6 km (5.96 km here), this yields close to 300 points for the full course. So then at each distance I can calculate the difference in times: the 2015 advantage, which I plot, is the 2014 time minus the 2015 time.

Here's the result:

plot

An aside: this is the first plot I've posted here done with gnuplot. In the past my plots have generally been from xmgrace or occasionally xgraph. But I've had problems dealing with the Motif toolkit required by xmgrace.

Last year I was dropped on the bottom part, but latched onto a group with Alexander Komlik. This year I hung with the led group to the turn-off (km 3.3 in the plot). The pace was fairly high, with a bit of a tailwind, but the not enough tailwind that the effect of draft was rendered insignificant.

After the drop off there was a short climb to the gate where I was dropped. The plot is perhaps consistent with this. Relative to last year, I was riding hard in 2015 to stay with the group to the start of the climbing again, but then I gave up and settled back unto what I considered to be a sustaninable pace. As a result I gained on 2014 time but then lost 7 seconds quickly.

Both years the climb of Radio Road was a matter of going as hard as I could as long as I could. I was around 5 seconds faster in 2014, perhaps due to the prominent headwind this year, although that was most observable near the top where I held even this year.

So while I was around 15 seconds faster overall this year, this time was gained all on Guadalupe Canyon From the turn-off to the park entrance I actually lost a net of 2 seconds.

I noted that the profiles were in agreement to only around 20 meters of distance, the difference varying during the race. Lines taken and therefore distance traveled tend to vary a bit, especially near curves. At my average speed it takes around 3 seconds to go 20 meters. So near where the speed changes a lot, for example where the climbing starts again after the descent, there might be an error of a few seconds due to registration error. For example, if I was riding 10 meters per second on a flat part, then slow to 5 meters per second on a hill, in one case I might have segments at 2 seconds, 4 seconds, and 4 seconds, while in the other case the points at the same distance would be 2 seconds, 2 seconds, then 4 seconds, yielding a shift of 2 seconds difference since the former data hit the climb 20 seconds sooner. That's not due to difference in fitness, just due to differences in distance to that point in the ride. But the time differences seen in the plot are apparently significant (substantially larger than 2 seconds).

The conclusion? Not much. I should have been fitter. But a race date of 1 Jan makes that difficult. I'd like to believe at my present fitness (29 Jan) I'd have done better.

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