Garmin edge 200

Philinmerthyr

I got a Garmin Edge 200 today. It's a great gadget and easy to set up and use.

The only problem I found was cycling down a path with tree cover the speed was all over the place.

Does this effect the average speed or distance of does it compensate for poor satellite reception.

I left my cateye computer on for today's ride. After 30 miles the Garmin showed 1 mile less distance and 0.5 mph slower. How accurate is the Garmin? The wheelsize may be a bit out on the cateye which could explain the difference.

Lightning

It will be fixed when you upload it, but it won't be as accurate as with a speed sensor. If you want accuracy you'd be better off getting a speed sensor for the garmin (or sticking with your cateye, provided the wheelsize is accurate).

Mikey23

not sure whether you can link a speed sensor with a 200

Lightning

Mikey23 wrote:

not sure whether you can link a speed sensor with a 200

You're right, you can't, my bad.

In that case, just use the cateye for instant readings and the garmin for recording the ride if you don't mind having both around.

Cannock Chase

Always remember that a GPS device will measure the horizontal distance of your ride. It's distance measurement will ignore any height you have climbed/descended. A standard computer which measures wheel revolutions will measure how far the wheel has travelled so assuming it is calibrated correctly the wheel based computer will always indicate a greater distance than a GPS computer. To get a true indication of cycled distance with a GPS computer, add the indicated distance and height ascent/descent.
Hope this makes sense I'm confusing myself.....

chrisaonabike

Cannock Chase wrote:

Always remember that a GPS device will measure the horizontal distance of your ride.

Is this true? Given that each GPS fix should include altitude, the computer should be able to add up the actual slant distances using Pythagoras. I assumed that the more modern ones would do this. Disappointing if they don't.

p1tse

Sorry cant help but interesting replies above to which I would like to know too

davem399

I would expect that it will take into account the vertical distances as well. A friend measures courses locally for the CTT and they now use a Garmin for this.

Cannock Chase

I try to think of it like this. Supposing you climbed up and down Blackpool Tower which I believe is 518ft high. In total you will have travelled over 1000ft but your GPS will still show zero distance as horizontally you haven't moved. So after a bike ride to give a reading of actual distance covered you have to add the GPS indicated distance and the ascent/descent distance together. On a long ride it's usual to have over 5000ft of ascent so doubling that to give ascent/descent gives over 10,000ft which is not far off 2miles (10,560ft).
Sorry if I am mistaken on this.

Mad_Malx

^^Sums not really correct unless you are cycling vertically.
I can only cope with metric:
1km horizontally and 1km rise (i.e. 45 degrees): by pythagorus you travel sqrt(1squared plus 1squared) = 1.41 km, not 2.
More likely scenario:
10km with 1km rise (10% gradient): travel sqrt(101)= 10.05 km. You only gain 50m over the 10km

or 100km with 10km rise: Travel 100.5km .
or 100km 20km rise (gulp): Travel 102km

It really doesn't make that much difference unless you are on VERY steep slopes.

Cannock Chase

Mad_Malx wrote:

^^Sums not really correct unless you are cycling vertically

I appreciate only Lance Armstrong could cycle up a vertical slope :roll:
Sorry about my maths. Yes you are correct. Been 45 years since I was at school..!!
I was just using the Blackpool Tower thing as an example of actually moving 1000ft vertically but nothing horizontally. Just not sure if the GPS takes this into account when giving its indicated distance travelled.

Lightning

The GPS does take into account vertical distance (based on their data, which might not be so accurate depending on the zones), but that wouldn't make much of a difference in the first place. Like I said, it's fine if you don't mind some lack of accuracy on instant speed while riding (specially under trees, etc).

wongataa

ChrisAOnABike wrote:

Cannock Chase wrote:

Always remember that a GPS device will measure the horizontal distance of your ride.

Is this true? Given that each GPS fix should include altitude, the computer should be able to add up the actual slant distances using Pythagoras. I assumed that the more modern ones would do this. Disappointing if they don't.

GPS devices will log altitude data. They don't tend to use it for anything else as GPS altitude readings are a lot less accurate than the horizontal position readings. You can see this by leaving a GPS device in one place and watch the location drift. The altitude reading will vary a lot while the horizontal position will not. To calculate instantaneous speed readings GPS devices tend to use the doppler shift of the signals rather than the horizontal position data.

chrisaonabike

wongataa wrote:

ChrisAOnABike wrote:

Cannock Chase wrote:

Always remember that a GPS device will measure the horizontal distance of your ride.

Is this true? Given that each GPS fix should include altitude, the computer should be able to add up the actual slant distances using Pythagoras. I assumed that the more modern ones would do this. Disappointing if they don't.

GPS devices will log altitude data. They don't tend to use it for anything else as GPS altitude readings are a lot less accurate than the horizontal position readings.

Granted, but is there really nothing in the software that can do intelligent things, like ignore anomalous alt readings in a series, and convert adjacent to hypotenuse based on an average rate of climb or descent?

Sure, the alt tends to roam around a bit, but it's not grossly out most of the time (not on my phone anyway - don't know about Garmin devices).

I'd understand them not bothering if the average error doing it by alt and Pythagoras was greater than the average error introduced by completely ignoring the altitude, but not otherwise.