Garmin 830 v8.20 grade calculation and elevation error

How do you know the route had 5k feet revelation gain?  If it is from a route planner that number may not be accurate.  How do you know the other GPS units were correct elevation wise?

I’ve done the course at least 5 times before with approximately 5100’, the route planner has about 5200’ which is well within tolerance.  Also, the grade lag / accuracy is disconcerting; i.e. after the descent this weekend it showed grade on the flats of -15% (slowly changed to zero) when it should’ve been -7% at most from history and there’s no 15% on the course whether on incline or decline.

Ive had concerns with elevation + grade for a while but after a week of climbing in areas I know well and not matching prior elevation / grades, the  problem has obviously been exacerbated. 
 

Wongataa is a ridiculous defender of GARMIN brand . Is a GARMIN FANBOY . No matter what is wrong with these lasts GPS , Wongataa will always says you that you are wrong and GARMIN is fantastic

Thank you for posting this!  I have an 830 running v8.20 and have noticed exactly the performance issue you describe.  I've been searching around everywhere for another user noting the same issue (misery loves company!).  I've set the elevation manually and noticed significant (+12%) drift - activity start and end points are identical locations, but the elevation is different.  It worked fine before the 8.20 update. FWIW, I used the Strava elevation correction an it fixed it up just fine, but that's an additional step that I really should not have to do at this pricepoint.

It's like having power seats with a memory setting in the car, having the guys at the car wash adjust the seat and mirror, and then you have a clean car but you no longer have the power seats with your settings on memory position #1 and so you fiddle to adjust the seat and mirror all the way home!

I'll be following along to see if anyone comes up with a fix/workaround and will certainly post one up here if I come across anything.

Go back to 8.10 firmware.

This is the procedure for downgrading to 8.20 --> 8.10.

Go to this webpage and download the file:

https://www8.garmin.com/support/download_details.jsp?id=14955

 allory also makes it available via dropbox, here

1. Connect your Edge 830 device to your computer using the micro-USB cable.
2. Download and unzip Edge830_813Beta.zip folder.
3. To revert to the firmware 8.10, place GUPDATE_810.GCD file in the \Garmin folder (in your PC). Rename the file to GUPDATE.GCD before disconnecting your device.
4. Disconnect your device from the computer, approve the update on the Edge, and wait for the update to finish.
   NOTE: If you revert to an older version of software, all of your settings will be reset to defaults.

Important: you will loose all settings and will have to reconfigure the whole Edge 830 again... what a pain. 

First time after sync with Garmin Connect or Garmin Express, it will ask for upgrading, just skip by pressing "X" button bellow the "Remember Later" message. 

D0es going back to 8.1 actually fix the problem? I suspect it’s because it’s software issue too, but don’t want to do this for nothing:)

It did in my case … but cannot guarantee. Try&See. 

I went back to 7.1. Everything including sensors and Bluetooth work perfectly. There is no current fix for grade delay. It has been FUBAR since day one on the 30 series devices except for the original 1030. 

Software updates shouldn’t break your device! And it’s not like this is a 10y old one! It’s barely 1y , what kind of QA test garmin has in place !! At least the have good customer service when you reach out, in my experience