I have been using a Forerunner 301 for a few months now and it seems to be consistently 10% short when measuring distance. That is to say that it tells me I've finished a 10K as I pass the 9K marker!
Has anyone else had a similar experience?
It was bought online from a Danish retailer, is there a UK arm of Garmin who could help?
0 ·
Comments
My Garmin is always out, but it is enough of a guide for me for pace and distance.
If you're 10% out, you must have a faulty unit, surely? What would be interesting would be to find some other people with Forerunners at the finish line (there are usually a few about) and ask them what readings they had.
Something to consider is where you wear your unit as I have noticed that this can cause positional accuracy to decrease and throw in some wayward positions - this can increase total distance. If I loose signal something as simple as swapping the unit to my other wrist can regain signal. What sort of terrain are you running in? Tall buildings can certainly effect coverage and accuracy (signal bounce?) as can trees (signal shadow?).
If you use software like (the exellent) sporttracks that can help identify where the signal problems exist and may help better understand where the error is occuring.
Also the position of the satellites the unit is tracking can influence accuracy - a satellite low down to your horizon will provide less accurate data than one that is at say 45degrees (mid way between your horizon and overhead).
On a side note, does anybody know a website that shows GPS satellite positions / coverage for a given location at a given time?
Also, I have found the problem everywhere: at home in Derbyshire where the tallest building is a two storey cottage 50 yards from my path and at most times there is nothing bar the clouds between my and the sky; and races such as along the dock road in Liverpool - again no buildings at all for much of the route - and a fairly rural route in Cheshire. I have also, however, used it in the very built-up city centre of Sheffield with the same result.
What stumps me is that if I look at my routes on a map it is absolutely spot on, so the device KNOWS with relative accuracy WHERE I am, surely it can then calculate the distance accurately. Does this mean then that the problem is nothing to do with GPS and positioning but with the software in the device miscalculating the distance between two accurate points???
I have been using SportTracks, I would be grateful if good,bad,injured could elaborate a little on your idea of looking for signal problems and I will report back.
& they do get back to you!.I had problems
with my 301 & they exchanged my 2mth old
Garmin for another new one!.
Little Miss Happy: sorry if I've missed the point but if what you are asking is why does it measure short when it draws a straight line then the answer is that straight lines are always the shortest distance between two points. Suppose that you are running in a circle and all is well for the first half of the circle, then you will have an accurate distance for the first half (ie report = actual). Suppose that the signal is lost for the entire second half and only picked up again at the end then the Garmin will assume you did a straight line right across the middle of the circle. You actually ran the same as the first half but it will report the diameter as its measured distance, D'Oh: it says you ran 3 miles in 30 minutes and you actually ran 4 miles in 30 minutes, distance achieved wrong, pace wrong. Just what you wanted!!!
This was told to me by a friend in the military who understands these things a lot clearer than I do.
Hope this helps
this may help to explain some discrepancies. But as already said 10% seems quite excessive.
Unfortunately my problem manifests itself everyhwhere in the same way. The data on the Garmin is out, the data viewed in SportTracks is out (by the same amount), and the data viewed in Training Center is out (same).
Amazingly last night I think the degree of inaccuracy was less. I plan to drive the route (new route) tonight to see what the car thinks various parts of it measure, but I am pretty certain that it was out by less than usual.
Maybe the Garmin is learning that things in our part of the world are never quite what they seem!!!
today's run produced a discrepancy between the SportTracks distance - 8.9 miles and Garmin 9.004 miles
which is interesting - it means they must be interpolating differently as they are using the same data
I assume where the route turns ot a dotty line on the Sport Tracks map is where the signal was weak - in Derwent Valley - steep sided valley with heavy tree cover
As for its ability to deal with the triangular nature of hills - well I couldn't comment becuase mine is 10% out on the flat. I don't know whether the Garmin attempts to factor in that info or whether it just reports the distance as though a flat course was run.
As a Derbyshire runner it might be worth a visit to Jacob's Ladder at Edale. With a climb like that and a map to measure the flat distance you'd soon find out!
When I download my routes to a Tracklogs map, it seems to me that if my Forerunner loses the signal (usually when I've made a sharp turn under foliage or near tall buildings) it assumes that I've continued in a straight line, and then makes stabs at getting me back on track until it's got a good fix again. Sometimes this route can be longer than the one I've actually run.
To answer GBI's question, I doubt if you could get a map of satellite coverage, because they're not geo-stationary. As GPS is an American system, the orbits are optimised for America and are often low in the sky in Europe. When the European equaivalent system, Galileo, is in business in a few years time, its orbits will be better for us.
Am going to use it tonight and try wearing it on the top of my arm to see if it makes a difference.
The run I did last night that seemed better was done with the Garmin on my wrist in such a way that the face was always skyward and on measuring it tonight in the car I find that it is now less than 0.5% out (0.03 miles over 7.4 miles). Bit less comfy on the wrist but working - woohoo!
Just about to go out for phase 2 testing on a known-distance route.
....maybe the car's out!
Our current car consistently reads 5mph faster than the gps on clear motorways where the gps signal will be good.- The last car always said about 5% faster.
I believe that one of the things the new garmin is meant to fix is the fact that the current one has its ariel in a less than optimal position when worn normally.
I guess we don't all carry our arms the same way.- so people who tend to hold them more straight/swing them more are likely to get worse readings than someone who holds them steady with the wrist as far away from the body as possible?
Yes, you can wear them under clothes and they'll work fine.
<snip>
The compact, lightweight and waterproof Forerunner 205 and 305 have a completely new design that "wraps" the GPS antenna around part of the wrist so that the GPS receiver has a better view of the sky while training.
</snip>
LP - do you have any evidence that cars are purposely inaccurate? I would be very interested to read it as I find it difficult to believe that a car maker can be allowed to put a milometer in that doesn't measure miles but measures 0.95s of a mile!!! It would make navigation very difficult and would also mean that when you bought a car that had done 10,000 miles it would actually say it had done 9,500 miles (somewhat illegal as far as I understand).