I bought a garmin 305 mostly to track millage for longer runs, but have recently started taking it on long rides also. I did a century yesterday and it said over 12,000 feet of climbing? I live in Massachusetts and the terrain is hilly, but not mountainous like some other regions. While riding , I noticed that the elevation fluctuated a lot. Could this fluctuation be causing the total elevation gain to go way up? Has anyone else had a similar experience, or did I really climb 12,000 feet???
I haven’t been very successful with the elevation changes either. I’ve got a flat grass field I run on and it sometimes claims a 300 foot elevation change that is more likely 6 ft.
I was doing some climbing this weekend and the highway elevation signs were generally within 5 - 20 feet of the Garmin readout. I thought that was remarkable.
The distance has always been very accurate. Since I live in the midwest I never looked at the elevation until I spent two weeks in Boulder. As far as I could tell the elevation seemed accurate to me. If you have any issues, email their technical support. They got right back to me when I had trouble with the multisport function.
Do you have the Edge or the Forerunner? The edge has a built-in altitude thingy, while the Forerunner doesn’t. For the Forerunner, if you upload your data to MotionBased, you can correct the elevations by checking the MB Elevation Correction in the activity options tab.
It is a forerunner. The elavation seems to be pretty close at a given point (top of a mountain), but I am wondering if the constant elevation fluctuation is adding a lot more to the total feet gained when you view the ride after. Maybe I will check out the MotionBased site. Thanks for the tip.
And yes - very accurate with distance. Less than 1 mile off from my flight deck computer after over 100 miles. Not bad!!!
I have a garmin I use in my car which gives altitude. Sometimes its spot on, other times its off a bit and other times it will not give an altitude reading at all. This bugged me so I did a little poking around on the web and the first thing that popped up were alot of warnings to pilots not to use their GPS units for critical altitude readings ;-). GPS is just not as accurate for altitude as it is for basic positioning. It has to do with the fact that they do not have an altimeter per se but rather calculate your altitude using some really complex geometry. Basically, the unit is continuously performing a calulation of your 3 dimensional location in space relative to the satelites its receiving then using a programmed model of the earth to calculate an “altitude” above sea level. I do not profess to understand the math involved but the few things I read constitantly stated that the number of satelites you are receiving impacts the accuracy of altitude readings more than for your basic position, so as you gain and drop satelites, you can see large swings in your altitude like you describe.
The actual elevation is probably fairly close, but the overall is probably very off, especially without some smoothing of some sort.
Basically GPS’s are only accurate within 5-15 feet or so in the X-Y and worse in the Z. In the XY this doesn’t matter unless you’re traveling in a rather tight circle. IOW your distance on a small track will be off far more than in a straight line. However in the Z it makes a huge difference because your movement in the Z is far less than the accuracy.
So let’s say you travel 1000ft in one minute and that hill has a rise of 10ft. Let’s say that your GPS takes a reading every 5 secs, it’s off by 5 ft worst case scenario opposites every 5 secs, and 7 feet in the Z. Every 5 seconds you travel 83.33333 ft. At the end of your 1000 feet your GPS would list that you traveled 1007.1 ft. However it would list that your total elevation gain would be closer to 50ft rather than 10ft.
Another way to look at it is this. Ride that 1000 ft zig zagging from left to right 10ft every 83.33 feet vs a perfectly straight line. Not a big difference really in overall distance traveled. Now picture riding the same 1000ft on a hill road that had a 14ft hill every 83 feet vs a flat road. HUGE difference.
Also look at it from this perspective. Satellites are far away. They rely on 3 of them to triangulate your position. These satellites are further apart in respect to the X-Y plane than they are to the object in the Z and thus are more accurate in the X-Y than Z.
For an example picture a black plate on a white wall 100 yards from you. Is it easier to see if the plate moves left or right or closer and or further from you? Same thing with satellites, with the satellites being your eyes. If you could spread your eyes further apart it would be easier for you to see the Z movement until your eyes were at 90 degrees to the Z axis at which time you would no longer be able to see movement in the either the X or the Y.
The more satellites you have the “wider spread” you have and the more likely you will see Z movement. I have no idea about how dropping a satellite effects accuracy, but as described in my other post if the accuracy is a far greater impact vs overall distance traveled.
Only the Edge 305 has a Barometric Altimeter, which will give a much more accurate Altitude reading than the Edge 205 or the Forerunners which use GPS to estimate altitude…
Well…I had the edge bike version. Almost the same thing as the forerunner. I just sold mine b/c I figured it is just a waste of money. However, I feel it was very accurate and one of the best sold in it’s market. It was a very neat piece of equipment. I just figured I needed to be training rather than looking at statistics. The only downside is that it didn’t come with wattage. I think I eventually need to start looking at watts. It was cool for a couple of weeks and then it got boring for me. Good luck. It is accurate and you can set your wheel size to it, etc.
One thing to be careful of with the corrected elevation, I did a race last weekend that went over a high bridge (5% for 1k up and down) loaded up my file in motion based and it showed a sudden drop off at the start of the race. Took me a while to realize that the survey data used to correct the altitude was the elevation of the river and not the bridge.
well i did a ride with a friend of mine who had a garmin and his elevation gain was through the roof. but another friend of mine told me that it is pretty accurate and what happens is that you may just climb a few feet and then back down a few feet and you keep getting gains in elevation. To say you ride up a driveway and then back down that will be gain in a garmin but may not register in a regular altimeter that uses barometric pressure as the gain is not measureable.
I used a Garmin 305 when I rode the entire Tour de France route. Each and every climb is well documented as to it’s start and summit altitude and my 305 was never off by more than 5-10 meters. I was actually surprised as I think altitude is done based on barometric reading and when climbing a >6000 foot mountain I would think the weather/barometry would change and altitude be somewhat inaccurate. But, it was always spot-on.
I set up an account with motion based and downloaded the track. On the 305, the total elevation gain was 12,000 feet and the motion based calculated it as 16,000 feet. This was the opposite of what I was expecting, so now I am really confused!!!
I had a long discussion on this subject few weeks ago somewhere on slowtwitch just search for gholmes you will find it…
One possibility is (especially if you don’t have autopause set) when you are standing still or walking around short radius the instantaneous altitude will fluctuate quite a bit.
I had 9000 feet in an hour and a half while my foretrex few years ago was just setting on my bike (no pause on the foretrex). So if you can get the tracks in a program where you can edit that out then you can get better reading. get301tracks.exe to get the tracks then loaded into topofusion is one way.
The other problem is the algorithm used to calculate total climbing… First you have to filter out all those wild ups and downs.
Once thats done and you don’t haven’t stopped withoug autopause for any long period then you may get more accurate results.
Maybe motion based does this don’t know but I’d be willing to bet you don’t have autopause set so when you were resting or walking very slow these fluctuations added to the climbing result and aren’t filtered out.
I find all 4 of my garmins(gps III,foretrex,forerunner 201 and 305) are pretty right on if I’m moving and not going in circles or in close radius makeing lot’s of turns.
I’ve looked at my profiles in topofusion for a im canada,hawaii,wisconsin,lake placid and of course florida and they seem to match profiles online
It all boils down to the algorithm used to calculate total climbing and how well the blips are filtered out…
Ever seen your hear rate points notice sometimes they blip way up or down same thing will throw your average off unless you edit them(polar lets you do this).
Same is true of gps tracks over the whole route will be pretty good but you have to be able to filter out the blips and keep moving they suck when your standing still…