Garmin GPS doesn't work well in wooded mountain bike trails in new york? You don't say. Clearly the device must be garbage.
Run your iphone GPS on the same course and see the results it gives you. GPS isn't magic, there's a radio signal traveling from 12000 miles away. Obviously obstructions will mess with the reception strength. That's why your radio goes out under a bridge, except your radio station is located 2-3 orders of magnitude closer than a GPS satellite.
Now a dedicated GPS device like a garmin is going to do WAY better than the one embedded in your smartphone, because it doesn't have the additional noise of all the other components running in the background. A device with GLONASS will do even better than that. Your secondhand one-time anecdotal experience seems at odds with the THOUSANDS of strava users who seem to do just fine tracking their progress.
With all due respect, your post is terribly misleading...
Before I got a Garmin 500, I used an iPhone 4 (using Motion-X GPS app) and later an iPhone 5 (running Strava app). When I uploaded my rides to Strava using the Garmin 500, many times one or more segments would be missing due to GPS drift. Segments which were curiously NOT missed with the iPhone 5. It's gotten to the point where I run the Strava app concurrently on the iPhone as a backup in case the Garmin 500 misses any segments, which is quite frankly ridiculous considering it's (an expensive) dedicated GPS device which should theoretically be better...
Here's a great example, a ride from San Francisco to Muir Woods, and then up a smooth fire road and then paved road to the summit of Mt Tamalpias and back. There are a couple short of segments that the Garmin missed, yet were recorded with the iPhone 5 tucked into a rear jersey pocket. One of these segments was in fact a KOM (Walsh Crusher). If you compare the two tracks, you can see that the iPhone generally follows the road more closely, especially under tree cover.Ride recorded with Garmin 500Same ride recorded with Strava app running on iPhone 5 in jersey pocket
So if it wasn't for the iPhone backup I would have robbed of a well-earned KOM!
This is kind of a big deal - after all, I've been told that the name Strava is actually a acronym for:
I couldn't figure out how the iPhone could consistantly track better than the Garmin (especially since it's mounted out in the clear on the front of the bike), but very recently I stumbled on an blog post that mentioned that the iPhone used a GPS/GLONASS chip. I poked around some more and found that Apple has indeed been using GPS/GLONASS chips in the iPhone since the iPhone 4s (released Oct. 2011). GLONASS capability is also why the Garmin 510 generally tracks much better and loses less signal than the Garmin 500; it's potentially seeing double the number of satellites. It's easy to compare rides on Strava as you can see which devices are used. There's no question that the Garmin 510 blows the 500 out of the water, plain and simple. Hell, my iPhone 5 consistantly blows the Garmin 500 out of the water! Most likely the Garmin 500 is using the same (outdated) electronics since it's introduction a few years ago, whereas smart phones are constantly evolving with newer and better chips. Needless to say, I'll be getting rid of the 500 and getting a 510.
Here's a Dec 2011 post from the chipset manufacturer Qualcomm touting the benefits of the GLONASS capable chips:GPS and GLONASS: “Dual-core" Location For Your Phone
It's borderline criminal that Garmin still hasn't updated the 500, they'd much rather sell you the more expensive 510. Some of us would actually prefer a smaller, lighter unit incorporating the latest chipset technology (go figure)...