UKH

Any clues from collective wisdom ...

GPS watch (suunto ambit) tracks altitude running ok - bit generous on ascent but within 10-15%, but in cycling mode all seems fine to begin with then it seems to think the central belt has mount Teide+ tucked in the lanes with altitude ever increasing until sometimes ceilings out at 10k.

for those that know their way around the suunto system - fused alti is ´on’ , and think altitude is being taken from gps only as gusts on ridgesline (running) played havoc with barometer.

thanks in advance 

Does it do that every time?

I once had an altitude gain of about 600m (or whatever) on a flat running track on an old Timex GPS system - iirc, it was basically the sum of the +/- error factor on height on that device.

I think it can (or, at least, could) be common, as the GPS altitude could be flaky, depending on the system.

gps isnt great for measuring altitude  with fairly large error range. Its why garmin and I think most others allow for altitude adjustment when viewing it on the computer which figures it out based on the map rather than what the watch thinks.

exhibit A ... 

My Ambit 3 summit went bonkers, allowing me to beat Killian Jornet's workouts, with 65,000m of ascent in a day.  I tried cleaning the sensor with an old tooth brush, which worked sometime, but the error kept coming back, so I bought a Garmin in the end.

Perhaps it's something in the air? My Garmin Fenix has gone screwy on altitude as well recently. I only use it for walking and use a Garmin Edge for cycling. When I view my route on Strava everything is fime and the high gain is at a sensible level, but viewed on Garmin Connect and Komoot I'm getting stupid figures like 70,000ft on a 4 mile walk! I guess Strava is taking the figure from map references and Connect and Komoot from the watch reading. I have been meaning to calibrate the altitude but keep forgetting... gonna do it right now... perhaps your Suunto needs something similar?

On Garmin Connect you can turn on elevation adjustment to do the same as strava.

Just to let you know, I calibrated the altitude and barometer on my Garmin Fenix and the next walk I went on had an almost identical reading elevation gain on Strava, Komoot and Garmin Connect, so perhaps that's the issue you're having as well?