Retro Grouch 

I just finished a 22 mile ride around Creve Coeur Park starting and ending at the Missouri River bridge. When I turned off my Garmin I found a read out that said 853' of ascent. 853'! Can that be true? There are some contours on the route that I rode but certainly nothing that I would call a real climb. Could 22 miles worth of those little ups add to 853'? Is there a reset button that I don't know about?

Looigi

What does the elevation plot look like when you upload the activity to Garmin Connect, RWGPS, STRAVA, etc.? If you ended in the same place you started, are the beginning and ending elevations the same in the plot? Also, in Garmin Connect, you can turn on "Elevation Corrections" to adjust the activity data to correct for drift and offsets. You can also compare total elevation gain between the various sites as they calculate it differently, some using the device data, some using their database data, and some using a combination, as does GC with EC turn on.

Also, if you lay out the same ride on a site like RWGPS, it will show an elevation plot of the ride based on its map data. See how this compares to the elevation plotted in GC with EC turned on and off.

Retro Grouch 

I'm pretty good with things that have chains and sprockets. Electronics not so much. I appreciate the effort but all that stuff you just posted might as well have been from that little martian in your avitar.

doctor j

Was there any change in weather conditions? If the GPS has a barometric altimeter, and if there was a reasonable change in the weather, an error in altitude is conceivable.

digibud

When you turn on your Garmin it will acquire a GPS until it's good to go but that doesn't mean it is totally centered. If you wait 15 or 20 min you will get a better altitude reading. Due to basic triangulation problems, altitude is never very accurate in a GPS like a Garmin which is why most models have a function that allows you to set a known altitude for a given GPS location. If you set that known location you will get a better reading, but even with that set properly and with your Garmin knowing the set altitude of your starting point, when you return after a 22mi ride you shouldn't be surprised to learn that you gained and lost a few hundred feet over a perfectly flat course and upon returning you are 200 feet higher than when you started. There is nothing you can do about this deficiency. It's why surveyors (in part) don't use mass market GPS devices. They simply are not that accurate with regard to altitude. I'll bet if you look at your data you'll find your altitude changed when you got back home too. In your manual, find if there is a way to set a known altitude for your home. You can probably find that information, reasonably accurately, on Google Earth. Short of that, turn on your Garmin well ahead of leaving to let it center as best it can. Do it with your heart rate strap attached if you use one so that it "sees" the HR monitor right off the bat or you may have to turn it off/on for it to find the HR strap and then it has to acquire satellites all over again.

Carbonfiberboy 

AFAIK a Garmin doesn't get altitude from GPS but rather from a barometric sensor. Changes in barometric pressure during a ride will affect altitude readings. If you don't understand explanations here, time to do some studying. A Garmin is not the most user-friendly device ever invented.

Looigi

!!!??? Martian? That's Colonel Bleep from the planet Futura here to protect Earth interstellar evil doers.

Duh.

njkayaker

Too vague. What Garmin? What route?

Here's a 18 mile ride with 400 feet of gain. All of it on the other side of the river.

Heritage Park, St. Charles / Creve Coeur Lake Loop - A bike ride in St. Charles, MO

njkayaker

Again, we need to be specific about what Garmin people are talking about

Most of the "fancier" ones (500/800, etc) use a barometric sensor. The devices can get elevation from GPS alone but using a barometer is more accurate.

Not by a lot, it seems. Unless there's a fast-moving storm moving in.

rm -rf

It sounds reasonable, if there were any hills or grades at all.

A ride of 100 feet per mile is usually considered very hilly. ( That doesn't sound like much. But if it's all up and down, with no flat parts, then the hills are 200 feet per mile "up", which is about 4% grade. Any flat sections will mean that the hills are even steeper.)

Your ride was 853/22 = 38 feet per mile.

Here's a local ride, Route 8 west, that rides along the Ohio River. The biggest hill is only 80 feet high. But all the little 20, 30 and 50 foot roller hills really add up.

My ride was 1546/29.4 = 52 feet per mile.

Or this ride from Loveland Ohio. If I select just the middle part from mile 5 to mile 25, that's 20 miles and 500 feet = 25 feet per mile. It's all flat Ohio farmland. On that whole 20 miles, the biggest "hill" is maybe 30 feet high.

njkayaker

+1.

If the device has a barometer, it won't need 15-20 minutes.

I have a barometric altimeter on my cycle computer and indicates gain and loss as pretty-much the same number.

Note that people (typically) are interested in elevation gain/loss and not absolute elevation. (You don't need to calibrate the device to a known elevation to measure gain/loss accurately.)

I suspect the more real hills you climb, the more accurate the measurement will be. That is, a "flat" ride probably produces elevation gains/losses that are close to the noise.

GPS was mostly designed to determine position on a flat surface. The other thing is that people are much more sensitive to elevation than they are to horizontal distance. For example, a 0.1 mile (500 ft) elevation gain might be more noticible than a 0.1 mile horizontal distance.

rm -rf

Some Garmins don't have the barometric sensor, and just use GPS for elevation. It's hard for GPS to be accurate on elevation without averaging a lot of readings, so it's not quite as accurate as the barometer ones.

But I did have my 705 jump up 200 feet in 10 minutes when I was stopped and a thunderstorm front rolled through.

Terex

I think people are trying to make things needlessly complicated. The Garmin is cumulative for every undulation in the road. Yes, you could have 853' in a relatively flat 22 mi. ride. Not need for big hills, or even anything that you'd call a hill.

Retro Grouch 

That pretty much proves that either my Garmin or it's operator is screwed up. I essentially rode that same route plus more loops around the lake but minus the big climb from the Upper Bottom Road to the Heritage museum. I've only got the entry level Garmin. I'm inclined to think there's something that needs to be done to zero the ascent reading that I'm not doing.

njkayaker

I suspect the problem is one of expectations. Your Garmin (if it's the 200) isn't really designed to measure such small elevation gain/losses.

Still vague.

I guess you mean you have an Edge 200?

The Edge 200 doesn't have a barometer. A barometer is pretty-much required for accurate elevation measurements (gain/loss).

If you are recording a new ride (not continuing a prior ride), you are resetting ("zeroing") the elevation gain/loss number.

Terex

From this ride 03/31/2010 Route in St Charles, MO, United States | MapMyRide it looks like there is 100' rise going up the bridge and another 100' gain on the east side of the park - which isn't shown in the profile posted by njkayaker. The ride posted was 20 mi and 587 ft. with two laps around the park, one in each direction. Looks like 853' is not out of realm of possibility in that area if there is actually 100' elevation gain on the east side of the lake. Is there?

I'm just interested in looking at mapmyride, google bike routes, etc. Haven't looked at these in a while and its fun to see improvements made.

Retro Grouch 

I'm thinking there's more going on here than I understand. I don't have a way to measure but I'm having a hard time thinking it's a 100' rise going up the bridge. There's probably a 100' rise on the east side of the lake but only if you climb the bluff rather than ride the MUP around the lake. Unless I'm doing something wrong I don't think that my Garmin gives very accurate ascent data. Feet of climbing isn't a stat that I find very meaningful anyway. If you start and finish in the same place for every single foot of climbing you always get a foot of downhill coasting.

Terex

You're the one on the ground, so I trust your observations in light of conflicting information. The next time you ride it, get a check of elevation at lowest point before bridge and at top.

And regarding your "feet gained equals feet descended/coasting comment"…If you start riding more, with more hills, the elevation gain becomes very meaningful. As for me, I would find a "How Much Your Butt Hurts After a Ride" metric on my Garmin very meaningful.

Carbonfiberboy 

If we want to understand our Garmin's elevation readouts, as usual we can turn to DCRainmaker:
Understanding Sport Device GPS Elevation Issues | DC Rainmaker

Retro Grouch 

Interesting. That's what I suspected. My Garmin doesn't have the barometer feature so it's accuracy challenged relative to altitude. Other than providing me with a statistic that I can brag the ascent readout on my Garmin is pretty much useless.

Dudelsack 

I hope this helps.

inside the Garmin is a little tiny hamster with a nasty sinus condition. When you go up a hill, the surrounding air pressure drops. It gives the poor hamster a sinus headache and he starts pounding his head against a tiny little wall with a sensing device that records each bang. The more bangs it records the more feet of climbing that occur.

After a while the hamster will lose consciousness and it doesn't work at all, so sometimes you have to change hamsters out.