Ski distances on holiday

ise wrote:

micric wrote:I'm with you on that one tino,we tried a watch style GPS,the joggers watch an several friends managed 45/50mph,some other mad bloke managed 87mph on a pair of Atomic Excellent IIs and took the beer honours that night,now ise tells us we're dreaming,that's depressing!

87mph? Not even close :lol:

Your small GPS isn't that accurate, what happens is that the speed is calculated between two points, both of which it got wrong :lol: I use a variety of GPS devices and it's common, it tells me on foot I'm hitting 70 or 80 mph sometimes, I'm pretty fast but not that fast :D

Maybe so! But i'd certainly use it to gloat about speeds i've managed :P It's a good idea, if the 55 mph was true, then fair play to him.. It was him and his brother decided to go straight, ski tips pointing down and just go... They both recorded their speeds and he managed 55 mph. Not sure what his brother's said it had reached!

When doing the Three Valleys tour last year, the GPS I had was frequently (and consistently) recording speeds of 85km/h. A few readings of 100+ km/h had me laughing, but I'm fairly sure a speed of 85km/h isn't unrealistic. The GPS is a fairly good one, didn't throw up more than a handful of false speeds when on a car journey of 7000km. Given that it was a good 60km/h slower than the fastest slalom speeds recorded (and bearing in mind that wind resistance increases with velocity squared!) I'd say it's far from impossible for us mortals.

Gooseh wrote:When doing the Three Valleys tour last year, the GPS I had was frequently (and consistently) recording speeds of 85km/h. A few readings of 100+ km/h had me laughing, but I'm fairly sure a speed of 85km/h isn't unrealistic. The GPS is a fairly good one, didn't throw up more than a handful of false speeds when on a car journey of 7000km. Given that it was a good 60km/h slower than the fastest slalom speeds recorded (and bearing in mind that wind resistance increases with velocity squared!) I'd say it's far from impossible for us mortals.

There's a difference between using it in the car and on the mountain, the GPS falls back to a 2D fix in the mountains a lot as you're in the shadow of the nearby peaks and can't pick up the satellites nearer the horizon. The infrequency of points over distance travelled in the car would tend to increase accuracy as well, or decrease inaccuracy. A 100m error on the GPS makes a big deal at 20kph and could double the measured distance betwen two points in 30 seconds, moving at 100 kph on the motorway the same error makes little real difference. Sorry to spoil the fun but this is just how GPS works in the mountains and it is something I know more than a little about :D

85kph isn't 60 kph shorter than slalom speeds surely? that would be 145 kph which would be fast for a GS or a Downhill. I think the Hahnenkamm would be around the fastest downhill and that tops out around 150 kph but this is professional ski racers in cat suits.

Around 60kph is the maximum recorded around various stations in Switzerland when SUVA went around with a speed gun, I can't see any reason to assume that was under measured in some way. It also makes sense, it's just what you would expect in terms of speed.

mark203 wrote:Back to the original topic, sorry

Wouldn't a GPS meant for hiking be suitable?

They show the distance walked between points, walked/skied?

No :D although they are more accurate than the receivers in, for example, phones, cameras or these "pod" type devices mentioned. As I just mentioned in the mountains you've a problem that a GPS tends to "see" a reduced number of satellites which reduces the accuracy of that fix. The advantage of a fuller GPS unit is that it will tell you just inaccurate it is, the maths is complicated but reliable so it can know that.

Garmin have recently upgraded their range to include to higher sensitivity devices, these models are prefixed by "H". With or without that feature you can fix the data yourself, they all link to a computer and display the track, by eye you can see that points that aren't accurate. Or you can work out what speed is reasonable and just remove those points, and then, by magic, you see the crazy points disappearing from the map. I have a tool that does that automatically and it's odd that something like that isn't widely available or that devices don't have it built in.

Again, like I'd already mentioned, part of the problem is short gaps between points, that means even small errors in the fix will give crazy results. Even walking I get speeds in excess of 100 kph while I know anything over 10 kph is stupid. Walking with a GPS you find the real gap between points is between 10 or 20 m, an error could be anything up to 50m so you could can see how inaccurate that would be.

If we're talking pure navigation then GPS is often a fiddle and an altimeter is much more reliable and useful.