nemeseri

So I will end up buying finally a cycling specific computer and after days of research I came to the conclusion that I will go with either the Garmin Edge 500 or 510. The only thing that holds me off from the Edge 500 is that my LBS said it has GPS accuracy issues.

I researched a bit and while I found some threads, most of the issues seems to be fixed by software updates and turning on the 1 sec recording mode. I'm sure tons of you have this device. I'd appreciate any feedback on GPS accuracy.

While the 510 seems to have a better GPS technology built in, I heard that it still has some software issues and it's much more expensive. Also I don't think I'd use any of the extra features.

SammyJ 

It tracks me right dead middle of the local MUP I ride.

gregf83 

The 500/800 are plenty accurate. The LBS is just trying to upsell you. There have been hundreds of thousands of 500s sold and are probably the most popular tracking computer out there. Unless you need the cellular link I don't think the 510 offers any real advantages.

rm -rf

My older 705 works much better with 1-per-second recording. That makes recording file sizes of about 1 mb per hour, which isn't a problem.

Here's an example, with the outbound ride heading north, uphill. Then the return is downhill with a right hand turn. You can see which side of the road I was on.
Each dot is a recorded point, closer together uphill, of course. 10 mph is about 14 feet per second.

nemeseri

What about if you compare it to Strava on an iPhone 5? I'd guess the Edge 500 should be more accurate. Right?

gregf83 

Not sure. The iPhone GPS should be accurate but I don't know if it updates as frequently (once per second) as the Garmin. The Garmin also allows you record HR, Power and Cadence if you're interested in that data.

Marcus_Ti

Accuracy wise they should be comparable...but the iPhone will burn a crapload more battery doing the same GPS task. And it isn't as durable.

gregf83 

Better than what? An iPhone or a 500? The 500 records at the same rate.

nemeseri

You can also pair your iPhone with any Bluetooth smart device, so it's possible to record speed / cadence / power. Unfortunately that will eat up the battery even faster.



I know that if I record my ride on my phone, that will eat up my battery. I was just wondering about the accuracy of the iPhone.

bahula03

In my experience, the 500 is a bit more accurate than my 5s, both being well above the "good enough" threshold. The only issue I've seen as being common with the 500 is that the barometric altitude/elevation readings, as absolute values, aren't super accurate...but the delta, what actually matters, is very accurate.

DrIsotope

That mirrors my experience precisely. Static elevation readings are usually off by a decent amount-- it reads my house anywhere from 700 to 1100 feet (it's at 1300ft) and riding the boardwalk at Huntington Beach last week registered -126ft, but the recorded amount of elevation gain/loss is spot on.

nemeseri

I just found this article and I think it's super interesting.
https://www.singletracks.com/blog/gps...dedicated-gps/

The only problem that it states the importance, but doesn't include the recording frequency for every gps device. It might make a huge difference in the case of the Edge 500.

Do you guys experience much less battery life if you turn the frequency to 1 sec?

Willbird

The iPhone 5s paired with a wahoo RFLCT+ is actually pretty thrifty with battery reserves. Close to 4 hours moving tine yesterday running Cyclemeter left me at 68% battery level. 4 hours 15 minutes total time roughly.IMHO the iPhone screen is the power hog not the gps, Bluetooth, etc. I was running the rflct+, wahoo TICKR, wahoo blue sc.

znomit

This.

rm -rf

I meant to say that my 705 is better with one-per-second recording than the uh, "smart" recording, which tries to just record changes in speed, etc.

Yes, my 705 is similar. You'd think that the Garmins would adjust the elevation when powered on and not yet started recording. But they don't.

A partial fix is to save your commonly used starting points, with the location GPS averaging turned on for at least 30 seconds. I can see the elevation converging to the correct height as it gets more readings. Hit Save. Then when I start a ride within about 100 feet of that point, I see "elevation point found" and it sets the elevation correctly. (It ignores saved locations that I pass by, only the one when starting recording is used.) There's a limit of maybe 50 or 80 saved locations on a 705. I had to clean out old ones when it filled up.)

The GPS averaged saved locations can be very accurate, within just a couple of feet of the actual elevation.

To save a location: On the 705: main menu-->Save Location-->Avg. It counts measurements , one a second, and the location and elevation update as each reading is averaged in. The elevation will stop changing after 30-60 seconds. Then hit Save.

gregf83 

Interesting article but it isn't representative of the accuracy you'll see under normal conditions. It's fairly well known that GPS devices aren't accurate when going around a track. You'll get much better results in normal conditions.

Battery life is not an issue for recording at 1S intervals. The reason Garmin originally used 'Smart' recording was to conserve memory not power. Since memory is essentially free now you should always record at 1S. I believe the Garmin 500/800 lasts at least 10 hrs. Longer than I've ever cared to ride.

Regarding accuracy, one thing I forgot to mention was elevation. Using an iPhone to record rides on Strava results in grossly inflated elevation data.

RALPHFELT

I have been having speed reading issues, I will be going at say 18mph easly and then it will drop to 15...17...back to 18 and so on. Is this normal? In one section where it is a downhill grade it will go from 20 to 14 and just keep bouncing for a bit.

dr_lha

Funny, when I ride with guys with Garmins, their elevation always exceeds mine as recorded on an iPhone 6 on the same ride.

I'm using Cyclemeter, maybe if I used the Strava App I'd "climb" more!

gregf83 

Depends which Garmin model and whether elevation is recorded using barometer or GPS. Could be an issue with Strava as well because the iPhone 6 has a barometer but I don't believe Strava uses that data.

nemeseri

Do you have a separate speed sensor? I think your actual speed based on the GPS can be off and that's normal.

This is really useful! Thanks for sharing.

The elevation change is not a big concern for me. As soon as strava starts to use the barometer in the iPhone 6, it's gonna be more accurate. And it's already quite accurate with the Edge 500.

If you want to deep dive into this issue you can read a long-long article about it here: Jeffrey Friedl's Blog » The Voodoo of Elevation Gain and Strava (and How I Get Around It)

Seattle Forrest

A cell phone can do a pretty good job with GPS in a city or suburb because it can use wifi networks to help with its location, which a Garmin cannot.

A lot of cyclists like Garmin's computers because they have long battery life, they're waterproof, pretty shock proof, and mount pretty well to your bike, they're also easy to see in the direct sunlight and to control while you ride. A thing made for cyclists generally works better than a thing you can make work for cycling. But phones can work pretty well too.

I've never used a 500 but have an 800, I've used it on every ride for almost 5 years. The GPS tracks are usually great. Garmin's new $500 triathlete watch has worse GPS quality than the Edge 800. The 500 is the same vintage and hugely popular.

dr_lha

Well I'm already using the barometric elevation on the iPhone 6 as Cyclemeter supports it, of course, Strava may toss those values out for it's own, I don' t know. As for it being accurate though, well honestly, often I appear to end on a different elevation than I started at, which considering I ride in loops isn't good! Barometric altimeters are all very well and good as long as the air pressure is constant. Guess what?

Seattle Forrest

Even with normal changes in air pressure, a barometric altimeter is still a lot better than GPS. It's currently the best we've got.

Ben I.

I have the 510 and love it, won't go into all the different features since from your research you probably know them. From researching when I was looking into getting a GPS unit last year, I found that the 500 can drop satellite fix now and then IF you're in very, very woody terrain because it only uses American GPS satellites and the 510 uses both American and GLONASS for signal. Most of the time this won't matter but the 510 will acquire signal a little faster and be more reliable IF you are in rugged terrain. As far as accuracy, I very much doubt that there would be much of a noticeable difference.

As far as using a phone, on longer rides you may have to worry about running down the battery since running GPS on a phone really drains the battery.

dr_lha

As pointed out above, this isn't really true. What drains the battery on a phone is screen and data usage. With "Mobile Data" turned off and a 100% charged iPhone 5 and a Wahoo RFLKT as my screen, I rode a 102 mile ride last year, with multiple stops, on a single charge. Not suggesting that a Garmin won't last longer than this, but I rarely do centuries.