Well, shoot. :mad:
However, you’ve now got me taking a more detailed look at this. I’d like to figure out another way to measure my speed, even if it’s only an average. The vertical drop and horizontal distance seem accurate on the app, and time is easy enough to measure. Top instantaneous speed would obviously be more difficult to measure.
FWIW, I just took a look at a run I did in the Canyons at Park City. It was the end of the day, so I know exactly how much time it took (4.5 minutes), because I was trying to catch the lift again before 4 p.m., and I didn’t stop on this run. The distance according to the app was 1.2 miles, with a vertical drop of 1,071 feet. The vertical drop matches the resort stats, and the horizontal distance matches Google Earth. The app says that my average speed was 16.2 mph, which checks out (simple math). It further indicates that my maximum speed was 24.1 mph.
However, it also shows a very detailed profile of my instantaneous speed vs. time, with a series of peaks and troughs as I made my way down. (I could post a screen shot if I knew how to post pictures here.) There are 5 main speed peaks (22.1 mph, 21.2 mph, 23.9 mph, 23.2 mph, and 22.1 mph) as well a series of troughs (11.5 mph, 8.0 mph, 14.4 mph, 14.2 mph, and 6.2 mph). Bottom line: the average speed of 16.2 mph seems consistent with this profile of instantaneous speed. Quick check: simply average all of the peaks and troughs, and you are very close to the listed average speed, which we already verified.
The app does indeed seem to overstate the max speed a bit (24.1 mph vs. 23.9 mph), but doesn’t seem too far off. Also of note is that the vertical footage calculated by the app is nearly identical to that of the EpicMix app (which simply keeps track of every lift you take). My app calculated a vertical footage of 118.9K vertical feet, while the EpicMix app came up with 119,178 vertical feet for the week at Park City.
For those faster runs at Stowe last season, conditions were nearly perfect, and I was running the same run repeatedly. Also, the run in question (Nose Dive) was in fact historically used for racing at Stowe. (The guy who built the run said: “Nose Dive is the ultimate. That is IT! It’s inviting, it’s not too particularly difficult, yet you can develop pretty good speed on it.” He effused, “Nose Dive is really good—if you want to take it easy and swing turns, you can, and if you want to pick up speed, you can get going pretty fast.”)
Looking at the profile of the run where I didn’t fall for the section in question, the speed peaks on the profile were 25.5 mph, 25.8 mph, 29.1 mph, 37.2 mph, 45.0 mph, and 41.6 mph. (The listed max instantaneous speed on the app was 46 mph.) The troughs were 21.7 mph, 19.7 mph, 25.5 mph, 28.0 mph, and 33.1 mph.
In short, speaking as an engineer and former physics instructor, the instantaneous speed profiles profiles produced by the app look plausible.
Finally, and this is certainly not scientific, I’ve been on a bicycle at comparable speeds (downhill, of course). It’s not too hard to tell if you are going down a hill at 20 mph or 40 mph. I felt very lucky that I didn’t get hurt when my skis slid out from under me on the run that I was supposedly going 47 mph. I slid for quite a while (seemed like an eternity). Fortunately it was a wide open, almost completely empty slope.