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  1. #1
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    garmin edge 305 vs cat eye stada? which one is correct?

    i have been riding with a wireless cateye for a few years and just recently purchased a garmin edge 305, i have been out riding with both of them a few times and at the end the ride the distance between the two computers is always different, the cat eye computer always reads at least a mile longer. i double checked the wheel size on the cat eye and is correct, anyone else have this problem? which one should i believe?

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    Quote Originally Posted by splitskater
    i have been riding with a wireless cateye for a few years and just recently purchased a garmin edge 305, i have been out riding with both of them a few times and at the end the ride the distance between the two computers is always different, the cat eye computer always reads at least a mile longer. i double checked the wheel size on the cat eye and is correct, anyone else have this problem? which one should i believe?
    How long is the ride? Also, is it really that important? No solution is going to be perfect. All have estimates built in. When programming your cat eye, do you use a preset? If so, that doesn't account for variations in tire heights between brands (making the same 'size' tire). Did you manually calibrate it? Weighted at your riding weight with gear to compress the tires properly?

    On the Garmin, what's satellite reception like? Terrain? Trail features? The way the GPS operates, it also has built in estimations of distance.

    If you want to know the TRUE distance of the trail, and therefore which device is closest to the right answer, you need one of these:



    Short of that, don't sweat the details.

  3. #3
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    I would tend to believe the Garmin more than the Cateye. I ride with an Edge 305 while my buddy rides with a higher-end Cateye but I forgot which model he has. At the end of a long ride our distances will be off by a mile or two. The way I see it, the Cateye system measures speed and distance based on wheel rotation while the Garmin measures speed and distance based upon the satellite signal received by the unit then calculated using whatever algorithm it uses. Since you are using a multiplier to input your tire diameter and different tire manufacturers make their tires in slightly different diameters you cannot absolutely get the correct number here. Also, you cannot input a decimal number, in case the absolutely correct number you should enter is something like 2187.3. The little bit of calculation error adds up over the miles.

  4. #4
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    Quote Originally Posted by splitskater
    i have been riding with a wireless cateye for a few years and just recently purchased a garmin edge 305, i have been out riding with both of them a few times and at the end the ride the distance between the two computers is always different, the cat eye computer always reads at least a mile longer. i double checked the wheel size on the cat eye and is correct, anyone else have this problem? which one should i believe?
    Both will have errors. The Cateye will be probably be off by more if you did not do an actual rollout measurement of your tires with weight on the bike and redo it when you changed tires.
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  5. #5
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    From what I've heard, the GPS mileage will not include the distance covered by altitude changes. So, if you have a lot of ascents and descents in your ride, you will get "shortchanged" by the GPS.

    In general, your GPS should be very accurate, so you can use it to calibrate your CatEye by riding on a flat road at a consistent speed and adjusting the CatEye to match the GPS speed.

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    Some of you put too much faith in the GPS. Don't trust one any more than the other. They're both off. How much? I can't say. Too many factors.

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    Assuming that the tire input circumference in the Cateye was done by rollout at riding weight & the riding was done on a relatively smooth surface, i.e. road, I'd trust the Cateye over any GPS.

    One way to find out how accurate both devices are is to compare them against the mileage on a known course traveled in a vehicle.

  8. #8
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    Find some railroad tracks that run along a straight, usually you can find some signs that say "begin measured mile," and "end measured mile." JAT

  9. #9
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    Quote Originally Posted by Sometimes
    One way to find out how accurate both devices are is to compare them against the mileage on a known course traveled in a vehicle.
    is your vehicle odometer that much more trustworthy?

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    Quote Originally Posted by thumbprinter
    is your vehicle odometer that much more trustworthy?
    In general, I'd say yes. At least to a 10th of a mile. Which appears to be a lot more accurate than the mile or so discrepancy being reported for the Garmin. If there are any doubts as to vehicle odometer accuracy just compare readings against mile markers. I've done that with a number of vehicles & they've all been good. YMMV (literally).

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    Better make sure your car's tires are properly inflated. The odometer is calibrated assuming a certain tire inflation pressure.

  12. #12
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    gps measures a flat world not accounting for altitude changes. If you remember your high school math the hypotenuse of a triangle is longer than the base. http://www.mathwarehouse.com/geometr...-triangle.html

  13. #13
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    Quote Originally Posted by ssbrix
    gps measures a flat world not accounting for altitude changes. If you remember your high school math the hypotenuse of a triangle is longer than the base. http://www.mathwarehouse.com/geometr...-triangle.html
    Not entirely right, but close. The GPS does have a general mathematical model for the world...the spheroid or ellipsoid (ellipsoid is more accurate, but I dunno which one Garmin uses), from which it bases many calculations. However, this model is not perfect, so there will be accuracy discrepancies because of variation in the real world from this spheroid/ellipsoid.

    So don't consider the GPS perfect. However, depending on calibration, the other computer could be even more inaccurate, so don't consider either to be the 'true' distance unless you've run a series of tests against a known distance to find out.

  14. #14
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    +1

    In my opinion, the line plots and the change in the altitude are some of the more overlooked differences in the mileage in GPSs. Your Garmin calculates distance based on the distance between points. If you ride a curvy line, the system can actually shave distance off the route because all the turns may not be calculated into the line. Plus it cannot calculate for the distance covered in the Z axis (vertical). The system can calculate your feet climbed, but it cannot translate that into a distance. So on a ride, you will come up short unless your trail is perfectly flat.

    You want to calibrate your Cateye? It is based on tire size. Go to a US high school running track. Four laps on the inside lane typically equal 1 mile unless it is a metric track. Ride eight laps for more accuracy. It will help you gauge the settings on your computer. But even if you have it perfected the settings right now, your tire diameter can change do to wear, pressure changes and terrain so it may not be accurate the next time.


    You know, roughly, how long the trail is. Like it was said, unless you get a really long tape measure or a rolling measure, you will only have an estimate. But you rode the trail. Is the exact mileage that important to you?
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  15. #15
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    So, if you go to motionbased.com and get a gpx file for some long race like the Breck Epic, Firecracker 50, or the recent Park City Point to Point, what this means is that the stated mileage of all of those GPS routes will be say 1-3 miles low due to the massive amounts of climbing in those races? Lame.

    I still think you lose more from the GPS cutting corners on twisty single track though. My Vista HCx is always about 10% lower than my bike odometer, and I compared my bike odometer to a riding buddy's recently and we were about dead nuts on... essentially the same. My personal opinion is that a plain old bike odometer is a lot more accurate for actual mileage than a GPS... but the GPS is a lot more fun )
    I read that on the internet.

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