Strava Question
Discussion
Because Strava is horribly inaccurate - it's especially appalling off-road - I've stone cold beaten my mates on sections - given them a 90 second headstart and finished on their back wheel and started with them behind me and had time to jump off my bike an hastily put a smug look on before they arrive and Strava will usually tell me I'm slower.
P-Jay said:
Because Strava is horribly inaccurate - it's especially appalling off-road - I've stone cold beaten my mates on sections - given them a 90 second headstart and finished on their back wheel and started with them behind me and had time to jump off my bike an hastily put a smug look on before they arrive and Strava will usually tell me I'm slower.
Inaccurate you say? Well I knocked this off in 20 minutes. Apparently.
This is my understanding, I am happy to be corrected if anyone can shed any light on this:
At any time your GPS positional accuracy could be 10ft or 100ft depending on all sorts of factors, it's not too much of a problem if you are moving quickly (airplane, car etc) but becomes an issue the slower you move. It is a real problem when running for instance so that GPS watches for running have to use all sorts of maths to try to give you a speed that is somewhere near correct.
The data in a GPX file is essentially a sequence of time, position and (optionally) elevation readings, if you consider the inaccuracies that could be present in the position and elevation you can see that, depending on the algorithms used by programs such as Strava, odd speeds and also gradients can appear. Fortunately time by GPS should be incredibly precise so you can trust that!
At any time your GPS positional accuracy could be 10ft or 100ft depending on all sorts of factors, it's not too much of a problem if you are moving quickly (airplane, car etc) but becomes an issue the slower you move. It is a real problem when running for instance so that GPS watches for running have to use all sorts of maths to try to give you a speed that is somewhere near correct.
The data in a GPX file is essentially a sequence of time, position and (optionally) elevation readings, if you consider the inaccuracies that could be present in the position and elevation you can see that, depending on the algorithms used by programs such as Strava, odd speeds and also gradients can appear. Fortunately time by GPS should be incredibly precise so you can trust that!
Zoon said:
Just a quick question for Strava experts.
I compared a ride with a friend and on the effort comparison it gives a current speed for that part of the segment. My speed is a couple of miles an hour quicker yet it shows me as behind all the way.
How is this possible?
To try to answer just this question...I compared a ride with a friend and on the effort comparison it gives a current speed for that part of the segment. My speed is a couple of miles an hour quicker yet it shows me as behind all the way.
How is this possible?
...what GPS units are you both using?
Some GPS units have a lower sample rate than others. I've seen segments where I KNOW I was faster than a friend as we were head-to-head racing on it. Yet when you hit play-back in the 'compare' feature, his icon regularly "jumps" ahead of mine as his 5 second sample rate is far less smooth than my 1 second sample rate.
It's one of Strava's limitations, along with hideous inaccuracy when, for example, using a 'cycling' GPS unit (Garmin Edge 500 in my case) to record running or hiking activities. I frequently get a time on a couple of local MTB segments when I'm riding parallel road routes to them. It winds the MTBers up no end, but hey? It's not my bloody fault!!!
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