1040 elevation gain data inaccurate - 25% too high

forums.garmin.com/.../fw17-29-all-elevation-bugs-are-not-fixed

Thanks for the reply.  Im not so concerned about the lag although I do see that.  The lag is what is the cause of the total gain to be so far off?  Would every unit have same issue?  Im trying to determine if its an issue with my 1040 or they are all like this

On some SW i had a lag but it gained extra ascent from nowhere

I have had the same issue. My 1040 recorded accurate elevation gain over known courses, but for the last few weeks has been registering elevation gain that is 30-40% high. I put in a ticket to Garmin and I got back a jumble of requests for data, etc. I just want the damn thing to work. I gave my old Edge 1000 to my wife and it records elevation perfectly. This is a big disappointment.

It seems the Edge 1040 doesn't filter out very small elevations so every speed change or wind change leads to a little elevation change due to the barometric sensor. These add up profoundly. 

I agree it's frustrating that it doesn't work as it should, but how is Garmin supposed to fix things without getting information from the users that run into problems?

On MTB there is massive lack of ascent, but on road bike it usually gives extra total ascent... 

Vote up here, may be it will help

forums.garmin.com/.../18-20-altimeter-readings-not-fixed

I agree, but the list of information requested is crazy. This seems to be a general problem with the Edge 1040. It was never a problem with my Edge 1000.

Here is the list of data and other items Garmin requested. I'm not even sure how to get all of this data:

• What dates can I compare that are the same routes where the discrepancy is? 
• So to confirm you and your wife rode the same route and the elevation between the 2 Edge's were very inaccurate? Can you send me the .fit files from each account for that activity? If you could also provided screenshots from her account and your account that would be very helpful. 
  On a personal computer sign into each account. Connect.garmin.com. On the left select the activities icon> all activities> click on the name of the ride so you see the details> on the top right there is a gear icon to click> export original. This will save the file to your PC. Do this for both accounts for the same ride and send that in. 
• I need pictures of the 1040. Front, back, top, both sides, and a clear picture of the bottom showing the charging port area. 

There are some big discrepancies in elevation / ascent data. My riding partner and I both use 1040s using the same rubber case and have differences that I don't recall we had with the 1030. The error swings in both directions indicating a lack of consistency. I have listed the comparative ascents recorded for each of us from rides of 11 miles to 100 miles for both road and MTB. I have a long list of rides together but these are just some representative samples as we've had around 100 rides together using the same equipment.

Here is a list of feet ascended for me followed by my friend:

817 - 909 - Local MTB ride
1,060 - 922 - Local MTB ride
3,419 - 3,058 - 100 mile road ride
737 - 955 - Local MTB ride
984 - 1161 - Local MTB ride
827 - 942 - Local MTB ride
6,818 - 6,818 - Lutsen 99er MTB Race

So, for the same exact ride / distance, sometimes he's higher and sometimes I'm higher. Random variation. The remarkable example is our Lutsen 99er Race (actually 86 miles due to rain shortened course) where we both recorded the exact same ascent of 6,818 which I find remarkable.