GPSrChive Discussion Forum

We'll we did a decent hike today. Montana was set at Trip recording when tracking. The trip computer screen was in sync with the saved track to BaseCamp so that works. But the wifes 66 had 300 ft less ascent. Same beginning and ending elevation. She also had the same total ascent as the trip computer and in Base Camp. Her's is set to "always" go figure. She always had the same ascent showing on her trip computer screen and shown in base camp.

Not sure who's gps is right. I have spikes in my track chart. Her's is more smoother. I carry it against my body in a shirt pocket she carries out in a pouch on the shoulder/chest strap area.

truckinguy wrote: ↑Sat Aug 17, 2019 7:33 pm Not sure who's gps is right. I have spikes in my track chart. Her's is more smoother. I carry it against my body in a shirt pocket she carries out in a pouch on the shoulder/chest strap area.

Neither will agree 100% with each other, nor will they agree with themselves 100% after repeated trips.

Where you are carrying the GPSr does have some affect on performance. It is theorized that when carried inside a pocket, some movements can create slight pressure changes in the pocket, which can lead to more erratic readings and more overall accumulated ascent when compared to a GPSr that is worn externally, such as your wife was doing, which is considered more stable.

I'm thinking the same thing about it all.

Main issue I have with my Montana 600, is when riding my bike. The stronger the headwind and/or the faster I go, the lower the elevation. It's all to do with where the BP sensor is located as it feels the increased air pressure from high wind-speeds.

One interesting experiment, is to place my hand in front of the airflow and then remove it. I can see the elevation increase a few tens of feet when my hand is there, and go back down again when I remove it.

Is there anything that can be done to isolate the BP sensor hole from the effects of wind when mounted on the top of the handlebars?

Mick.

Mick, behind the four tiny holes the Montana use to sample atmospheric pressure is a soft membrane that prevents water from entering the device.

If you wanted to try something, I might suggest placing a small piece of scotch tape over those four holes and riding again to see if that counters the headwind affect you experience, and to test if the unit can still properly sample atmospheric pressure correctly.

Let us know your results!

Tape?
Would that not stop the BP system working properly?
It would seal the air pressure, would it not?

I could try it. Off on a ride tomorrow morning. It was two weeks since I've cycled until this morning, and as I'm in my late 60s now, I need to keep at it to keep my fitness up. 18miles this morning and hopefully another 18 tomorrow. The weather has been wet and windy for a while, and I've been doing other stuff to keep me occupied.

I'll stick some tape over the holes before the morning, and I'll experiment on the exact same ride to see if the elevation trace is the same. I use AppleMacs and have a program called Ascent that I have all my bike rides uploaded into from way back. If I do the same ride as yesterday, I can compare them.

See you tomorrow!
Mick.

PS:
I know the absolute elevation of our front door at 222ft, and I always let the Montana settle for a few minutes and then calibrate the altimeter before leaving.

Mick.

That's why I suggested scotch tape, or similar. Very thin and flexible. Certainly do not use duct tape! 8^)

You could even apply the tape with a 'bump' over the area of the barometric sensor holes, so 'ram air' does not impact directly, but the unit still samples via small opening at either side of the 'bump' in the tape....

Mick F wrote: ↑Tue Aug 20, 2019 6:57 pm PS:
I know the absolute elevation of our front door at 222ft, and I always let the Montana settle for a few minutes and then calibrate the altimeter before leaving.

Mick.

It's when your moving that effects it. My wife's 66ST did the same as the Montana in my pocket on a 6 mile 1800 ft gain hike. When she carries it in an pouch out front on her pack shoulder/chest strap it reads perfect.

Same ride done, identical to yesterday's ride. 17.5miles.
This time, I had a piece of Sellotape over the BP holes but left a small hump. As I stuck the small piece on, I laid a pin across, then extracted the pin.

Total ascent of yesterday was 1,888ft and today was 1,939ft. Whether that's significant or not over 17.5miles, I don't know, but I do know that it's a nice hilly ride!

The wind was quite brisk, so on the flatter parts against the wind, I put my hand over the front. The elevation went up by 10ft, then back down when I removed it. Considering my elevation was 500ft at the time, that's an increase of 2%. Previously, without the tape, it could have been 10% or more.

This idea has merit, but it needs a better solution than a bit of sticky tape. I must give it some thought.

Mick.