Modeling time difference between Devil Mountain Double and Terrible Two

I previously described a heuristic but fairly comprehensive bike power-speed model. This was based on trying to model speed directly from course features, rather than going through power, since riders typically don't ride at a constant power, although that represents a physiological constraint. The model assumes riders have a given cruising speed on flat roads (I assumed 30 kph), a theoretical maximum rate of vertical ascent (I assumed 1300 m/hr), and a safety-limited rate of descending (I assumed 14 m/sec = 50.4 kph based on conditions on these courses; perhaps this was slightly low). I assumed a rate of fatigue of 0.5%/hour, which affects climbing rate (directly) and speed on the flats (1/2 as much). The model further assumes riders lose distance versus time when they turn: 40 meters per radian of cornering at max descending speed, much less when cornering slower (proportional to speed squared). I have compared this model to actual rider data and it seems to match fairly well.

With these assumption, I get the following ride times for Devil Mountain Double versus Terrible Two:

Terrible Two:313 km in 13 hrs 15 min 28 sec
Devil Mountain Double:330 km in 14 hrs 2 min 36 sec

So Terrible Two is definitely faster, as promised by Quack Cyclists. The difference for this sort of pace, however, is 47 minutes, not the two hours warned by Quack Cyclists, although their focus group for this warning is riders at threat for not making the course cut-off, and for longer times the gap will be larger, not necessarily in linear proportion.

Here's more detail: time difference

Devil Mountain Double falls almost 40 seconds behind by the Diablo summit, then gains some back on the descent, but then loses time out to 100 km. Terrible Two loses time here with the tough Geysers climb. DMD falls behind again, but Terrible Two does the hard section of Skaggs Springs Road, and DMD actually pulls ahead by up to 7 minutes. But T2 has a relatively fast run on the coast (the model isn't considering the wind here, which is typically a tail wind, making Terrible Two even faster here) while Devil Mountain Double deals out the challenging climbs of Mines Road and Sierra Road. By 297 km, DMD is ahead again, falling only slightly behind by the time Terrible Two completes at 313 km. But there's still 17 km left in DMD at this point, so DMD end up being 47 minutes slower.

Of course many factors affect this result: wind, heat, cold, darkness (although 14 hours is fast enough to finish DMD in light). An additional factor favoring T2 is more opportunity for pacelining, as was pointed out to me by John Murphy. The basic conclusion, though, is differences in terrain are a relatively small factor: DMD takes longer because it is longer.

Comments

Post a Comment

Popular posts from this blog

Marin Avenue (Berkeley)

Image
On Saturday, I got an email from Tim telling letting me know that Murphy's Spring Classics was going to start up Marin Ave. I'd missed that. Murphy announces his courses the day before, and indeed it was already well into the night before when the course announcement went out. I'd skipped over the details, jumping straight to middle and end games. Marin? I laughed at the irony, because not long before when he'd told me he was choosing to repeat the Nifty Twn Fifty which we'd done together last year versus selecting Murphy Mack's Stage Mullett two-day, I responded I didn't think I had it in me to ride Marin Ave two years in succession. Well, so much for that. I was committed, so I went downstairs to swap my 11-26 cassette for my Recon 12-27. The name is easily overlooked: "Marin Ave" fails to strike the same impression as, for example, "Redwood Gulch" or "China Grade". But among those in the know, Marin Ave is infamous i...
Read more

hummingbird feeder physics

Image
I couldn't figure out how the hummingbird feeder worked. Why didn't it overflow? Forces need to balance, of course. Neglecting surface tension, there liquid level is higher in the inner reservoir than in the feeding chamber, so there must be a corresponding pressure difference. Suppose the pressure in the inner chamber were zero. Then the column height difference would need to be atmospheric pressure / (density of liquid × gravity). But this is over 9 meters! Obviously the height difference is only approximately 1% of this. So the pressure difference inside versus outside is only approximately 1%. The inside is only slightly below atmosphere. So air is getting in. How? Does it diffuse through the liquid? If this were the dominant mechanism, it wouldn't take long for the pressure inside to go from 99% to 99.3%, for example, which should be plenty to push the column of liquid down in the inside chamber and thus push liquid out through the holes. It would over...
Read more

Gallium Pro geometry

Image
On Caltrain yesterday, I was surprised to see among the usual set of commuting bikes a SRAM Red-equipped Argon Gallium Pro. The bike immediately stole your attention. The design was one which has been trending: clear-coated carbon with plenty of text detail so the viewer is sure to realize he's gazing upon the result of advanced, proprietary engineering and not at yet another paint job on the same old OEM frames being pumped out of the same old Taiwanese factories. But it worked: the bottom bracket area was huge, the downtube a large-diameter "inverted Kamm tail" design seemingly designed to maximize wind resistance, the top tube a broad, eccentric shape which screamed "vertically compliant yet torsionally stiff". All it lacked were the pencil-think seat stays Cervelo popularized, but this was a machine designed for stiffness over anything else. It seemed dramatic overkill, since the bike was small (the Argon "XS" I suspect). There wasn't muc...
Read more