Karoo 2 elevation (meter climbed) reading 4-5 times more than it should be (last night ride 70km and 1236m when it should have been 340m).
Also while riding the grade would ALWAYS go all over the place.

So I found the reason or the culprit of all this craziness!!!!

How and why would the computer mount affect this??!?!?!??!! When I place the Karoo on the new mount on the new bike, all the elevation values are out of whack. And I mean at least 4x higher and I noticed the elevation changes all the time from -10 to +10deg even going on a flat.

By dumb luck I placed the Karoo on a temp quick mount on the stem of the handlebar. Everything is PERFECT!!!! What? Why? Is it the out front mount? Why???!?!?!

I have 4 bikes, all with different mount and never an issue. All using Garmin mounts. Never an issue and VERY accurate readings.

This new one, is the only one with the two screw installation. I have tried to add padding etc. Nothing. Today I got two different mounts with the same design see if that changes anything. Maybe its the material?!?!?!?!

https://m.media-amazon.com/images/I/...1000_QL80_.jpg

Blocked hole for barometric sensor ?

The problem with that theory is that a blocked port would generally result in very small elevation changes.

Explain why. I know Garmin’s use the barometric sensor exclusively for elevation determination and changes, not GPS. If the unit detects the barometric sensor is not available, will it then default to using GPS, which could make errors in any direction.

If the port becomes blocked, the pressure at the sensor (inside the Garmin) would not change, and it would show a non-changing elevation. The sensor would still be fully functional, but its output would be meaningless.

A Garmin would need software that can determine when a port is clogged if it were to switch over to GPS altitude. I don't know if they can do that.

Difference in harmonic vibrations while in use?

Device may be sensitive to differences in vibrations from the mounts being used. Try just carrying your device in a pocket, see what you get out of it.

Possible too that the unit you bought is defective. You'll need something else capable of measuring changes in elevation to bring you numbers you then can compare to those you're getting from the Karoo. Googling <karoo 2 elevation wrong> brings up lots of potential causes....

That all makes sense, thx

Defective unit makes sense. Swapping to a friends Edge and see how that works is a thought,

Turbulence around the hole adding noise to the reading?

Orientation of the barometric sensor hole? Toward airflow produces greater pressure. Air blowing across hole causes lower pressure due to Bernoulli effect. If airflow is funneled into that area (venturi effect), you'll get accelerated flow, with even greater pressure drop, so reading higher altitude. This is all just guesses.

I guess you only got through the first sentence of my post lol
No the unit is perfectly functional.

Since no one got through to the second part of my post, I am posting this again

I have 4 bikes, all with different mount and never an issue. All using Garmin mounts. Never an issue and VERY accurate readings.
The unit, Karoo 2, is perfectly functional.

Are you discounting znomit 's response?

You only had this issue once. Or at least you make it seem that way. Yet you "fixed" the one time issue by changing something. May as well have been possibly fixed by you changing jersey's.

Perhaps if nothing else mounted near the device created the turbulence, then it was just the angle and speed of the wind and gusts that caused your device to be off for that one day.

Once??? Nope, every time I went on a ride like this, maybe 20 in total. Then when I placed the unit on the stem, another 10 rides or so and all was well.
Not a single time did I ever need to adjust the elevation on any of my other bike(s) rides.

Those two statements aren't mutually supportive.

That you may believe it's perfectly functional may be preventing you from finding out why the data you get from it isn't what you expect or approximates what you're getting from other, similar devices used in essentially the same manner.

The ram air or cross flow idea has a little merit, might be fun if you can correlate it to your speed. But it shouldn't stay wrong, once you at or near rest and there is no longer any dynamic pressure.

Another is that this specific mount might be inducing a twist or bend that strains the little pressure sensor

My Garmin can briefly record excessively steep grades if I zoom down a steep downhill, then immediately climb the other side. The sharp change in wind speed at the tiny barometer hole confuses it temporarily. It's otherwise okay.

Karoo 2 elevation error complaints
A quick google search shows lots of forum posts on various sites about Karoo 2 elevation errors.
google: "karoo 2 excessive elevation gain"

This post shows their elevation chart, with repeated short, sharp elevation spikes in the middle of normal road grades. More often on downhills, but also on flats and climbs. The summary says "max grade 55%" !!
There doesn't seem to be an accepted solution that works for everyone so far.

I think elevation discrepancies and errors is likely the most common complaint about GPS cycling unit, Hammerhead, Garmin, whomever. It's generally know that GPS alone is terrible at determining elevation and I think barometric isn't much better from all the complaints I see.

Just to be clear:

OP has one computer
OP has four bikes, and each has a mount for the computer
Three of the bikes work perfectly
One bike works poorly
The poorly working bike has a different model of mount
The OP has a different mount that will allow the computer to work perfectly on the problem bike
All of this seems to point to a problem with that particular mount

The computer elevation failure is a very specific, repeatable problem
The computer does record altitude in the correct direction, but at a much high rate than it should
In addition to elevation, the computer also has incorrect, wildly swinging grade outputs

I am not familiar with this computer, but I'll take a guess that fits the above observations. I image the computer has three ways of determining elevation - GPS computation, relative barometric pressure, and dead reckoning based on speed and grade. It likely monitors these three things continuously while it's moving and outputs to the user what it thinks is the best information without bothering to tell the user what that output is based on.

I think the elevation is a symptom. The real problem is the angle of attack sensor in the unit. The sensor works fine in most mountings, but for some reason acts erratically in this particular mount - perhaps it just shakes or resonates the wrong way. Nothing in the computer is broken.

The computer unfortunately is not smart enough to realize that the input from the angle of attack sensor is garbage, so it weighs that input heavily in its elevation calculation based on whatever algorithm it uses.

The rest is obvious. The bike shakes the mount. The mount shakes the computer. The computer shakes the angle of attack sensor (it shows this on the screen). The computer uses this overly rapidly changing angle of attack data to dead reckon an elevation calculation. That dead reckoning is 4x too high because the computer thinks you are constantly going up and down little tiny hills.

The OP doesn’t clearly indicate, but Hammerhead makes a proprietary mount for the K2 where the unit slides into the mount from the rear, not the quarter turn round mount as used by Garmin. HH provides an adapter for the K2 to use with Garmin quarter turn mount, that adapter installs on the device, which from what I read is what he is using on 3 of the 4 bikes, with the 4th bike using the Hammerhead mount. Possible the HH mount is causing the barometric sensor problem. I used to own a K2, was active in the Hammerhead FaceBook group and cannot recall anybody ever complaining about this kind of problem, but would suggest to the OP that he join that group and post this problem.

Exactly this. I was not able to install another mount and go for a ride due to weather here, but will do so this weekend.

Ohhhhhh my lord. Not a single time did I mention using the original Karoo mount anywhere in my post.
Sometimes I wonder if ppl actually read the posts.
Anyways, when I install another mount (which I have coming shortly) I will post back and see if that helps. Right now it works good on a simple garmin rubber and elastic top of the stem mount.

Yes, you are correct. A re-read shows you using all Garmin mounts, apologies. As well, don’t be so sensitive, people here are trying to help. If you get testy, that help won’t be found,

FYI, IMO and all sorts of others....

I don't even have elevation or grade shown on the pages of my device that I use most often. They really serve no use in real time.

I really like to know how much more hill/mountain there is when I’m on an unfamiliar route. I find elevation very useful. I don’t find grade useful at all, that’s obvious from what gear I’m in.