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  1. #1
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    How to get accurate mileage?!

    So ive been using a cateye enduro 8 for a while thinking I was getting pretty accurate readings. This week for the first time I rode a trail that had mile markers and realized it had over read by half a mile by the 2 mile mark. Then I rode another trail that at the highest estimates is about 11.5 total and I had 17.98 miles on mine...
    I did a role out when I installed it and seemed to be getting decently accurate mileage until recently... WTF?

    Ive been using Strava lately as well and noticed that I REALLY like having the extra data so easily assessable, but sometimes the service comes and goes... so I bought a Garmin Edge 500 today.

    Somehow I missed all the less than positive reviews for this unit on super tight trail riding, which I do. Extremely tight. So now im thinking this will just be another inaccurate tool. Thankfully I bought it at REI.
    I read that using the wheel sensor is the way to go, but then Its basically just a fancy cyclometer? Could the same in accuracy accuracy similar to the cateye?

    Dammit I know its only $50 more for the sensor but the Edge 500 was already more than I wanted to spend...

    What I really want out of a unit is speedometer (max,average,current), timer/time, being able to map my ride and save and compare progress, And most importantly DISTANCE.
    Other things that are nice are the calories and elevation gain but nowhere near necessary.
    I don't care much for cadence and Heart rate and a few other things on the 500.

    Does such a device exist within a reasonable cost? I looked into the Edge 800 and that's just more than I think I need ever.

    Anyone else in this boat with me?

  2. #2
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    In my experience many trail mileages are way off.

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  3. #3
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    Well Strava and those particular markers matched up, as well as claimed mileage by the local
    MTB club for the overall trail length. I'd figure at that point the Cateye is the weak link.

  4. #4
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    If you set the sample interval to 1 second, you should be just fine on the twisty trails. It is at least worth a try to see how close it is before you take it back.

  5. #5
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    What I'm really wondering at this point is what is the most accurate method for measuring those things? Are there surefire reliable ways or is it all ballpark?

    Also this thing is sitting next to me on the couch and the movement alert keeps going off telling me to start the timer. This things steady at .5/7 mph and spikes up to 2/3 mph...
    What the hell is all that about?
    Last edited by Jaysop; 09-08-2012 at 08:27 PM.

  6. #6
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    Yeah, it is all ballpark. Accurate calibration is the best you can do.

  7. #7
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    Quote Originally Posted by Jaysop View Post
    What I'm really wondering at this point is what is the most accurate method for measuring those things? Are there surefire reliable ways or is it all ballpark?

    Also this thing is sitting next to me on the couch and the movement alert keeps going off telling me to start the timer. This things steady at .5/7 mph and spikes up to 2/3 mph...
    What the hell is all that about?
    Do you do an actual wheel rollout to get the correct calibration number for the Cateye? The wheel size charts and built in settings are just estimates.

    No rollout. Inaccurate results.
    mtbtires.com
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  8. #8
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    Yea I did a roll out, marked the floor at the valve stem, put my weight on it. Rolled, marked and measured. That seemed to work well for a time. Now it seems to be off.

    How accurate are odometers on cars?

  9. #9
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    Make sure the Cateye didn't get reset back to it's default calibration.

    A small consumer GPS is not going to be 100% accurate, as you noticed when it is sitting still inside your house. That GPS is accurate to about 15 meters or around 50 feet. So, every second, it's going to think it's somewhere else in that 50 foot circle. Since it keeps locating itself somewhere else in the circle, it will calculate how fast it must be moving to get from point A to B. Being indoors, the accuracy will be somewhat worse.

    I've noticed that my $500 62STC is just as inaccurate. When I walk a trail, the path and distance is very accurate in comparison to when I MTB it. When I rode a dirtbike on the same trail, the distances and corners where considerably shorter, even with one second sampling. Being under a canopy is much the same as being inside with regards to accuracy.

    My 305 is more accurate when using the speed and cadence sensor than the 62stc. I forgot to turn the sensor on when using the 62stc.

    To add a bit more: garmin.com/aboutGPS
    Last edited by RidingMyTrail; 10-06-2012 at 08:05 PM.

  10. #10
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    15m is pretty worst case scenario. It is usually much better than that. I'd say when I ride, better than 90% of the track is pretty spot on. The rest usually within 5m or so.

    It varies, of course. Some days are worse than others. But generally the GPS is pretty good, and the slower I go the better. When mapping trails walking pace is best.

  11. #11
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    Quote Originally Posted by NateHawk View Post
    15m is pretty worst case scenario. It is usually much better than that. I'd say when I ride, better than 90% of the track is pretty spot on. The rest usually within 5m or so.........
    +1 on that it's very rare my edge 800 will report an accuracy worse than +5m usually 0 to 2.
    If you want super accuracy on distance / speed etc use the sensor with the edge 500 and don't use the auto detect feature for wheel size measure it and dial it in. I use the speed, cadance, heart rate monitor on my road bike - but not on my MTB. I have used it without the sensor on my road bike when the battery ran out and distance / avg speed was pretty good within 1 or 2% accuracy when compared in TC.
    Compared to a mate with an Iphone it is a lot more accurate - his route is always pretty badly out and the speeds were all over the place (even though we were drafting in a group). The batteries tend to die real quick when using GPS with smart phones

  12. #12
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    Quote Originally Posted by NateHawk View Post
    15m is pretty worst case scenario. It is usually much better than that. I'd say when I ride, better than 90% of the track is pretty spot on. The rest usually within 5m or so.

    It varies, of course. Some days are worse than others. But generally the GPS is pretty good, and the slower I go the better. When mapping trails walking pace is best.
    I agree, but I just wanted to point out how that GPS isn't as spot on as some people may believe. Something fun to look at is turn on a GPS, clear the current track and let it sit in one spot for a hour or so. Go look at the current track. It seems that my GPS has had quite an adventure when I wasn't looking.

  13. #13
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    Quote Originally Posted by RidingMyTrail View Post
    I agree, but I just wanted to point out how that GPS isn't as spot on as some people may believe. Something fun to look at is turn on a GPS, clear the current track and let it sit in one spot for a hour or so. Go look at the current track. It seems that my GPS has had quite an adventure when I wasn't looking.
    that's no surprise. I have used GPS receivers enough over the years that I know how truly bad they used to be. No, they're not perfect. I think it takes a real idiot to expect that much out of them. But then again, nothing is perfect. I have also seen a couple of different Garmins outperform survey-grade receivers when collecting line (track) data. The Garmin can't outperform them when averaging a point, but Garmin has developed some very outstanding correction algorithms to produce very good track accuracy.

  14. #14
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    I just rode my local trail with both GPS receivers on the same ride. It was interesting that there was a three-tenths of a mile difference between the two over a 6.8 mile ride. I believe the speed sensor on the 305 helps quite a bit with the dead reckoning of the unit when the satellite signal is lost. The 62stc actually got confused on a switchback and had me reversing course and looping back over the trail. That was strange looking.

    I still wonder if his Cateye was somehow reset or maybe he changed the battery and lost his roll calibration.

  15. #15
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    Quote Originally Posted by RidingMyTrail View Post
    ...maybe he changed the battery and lost his roll calibration.
    That sounds like a pretty likely situation.

    switchbacks are pretty tough for GPS receivers to pin accurately, especially going downhill. They fall into the ~10% of the time that accuracy is limited for me. However, I don't think any of the Edge receivers do any sort of dead reckoning if the reception is lost. Dead reckoning would require the device to have sensors that monitor its orientation and an accelerometer to track changes in direction. This is what's going on with indoor navigation in smartphones right now, and it's hardly perfected even though most smartphones do have those sorts of sensors. The sensors just report speed, cadence, and distance so even while you have no position information, you at least have some info.

    The Edge 305 is widely believed to have outstanding reception even compared to newer models. I think the old Sirf III chipsets were just outstanding and I think Garmin switched to MediaTek as a chipset supplier some time back. Those chips seem to suffer some limitations in certain situations. I bet if you hooked your 62 to an external antenna mounted on your helmet or pack, you'd have improved results in your track.

  16. #16
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    Quote Originally Posted by NateHawk View Post
    The Edge 305 is widely believed to have outstanding reception even compared to newer models. I think the old Sirf III chipsets were just outstanding and I think Garmin switched to MediaTek as a chipset supplier some time back. Those chips seem to suffer some limitations in certain situations. I bet if you hooked your 62 to an external antenna mounted on your helmet or pack, you'd have improved results in your track.
    That's interesting information. I'm not actually too concerned for my use. Like you said, it's good enough for what I need. I just chimed in to try and help the OP. I got the impression he was expecting it to be uber precise.

    Oh, the cell phone point is well taken. I was thinking about how little the location on those move compared to the dedicated GPS units.
    Last edited by RidingMyTrail; 10-07-2012 at 08:42 PM.

  17. #17
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    Speedometer accuracy:

    Speedometer - Wikipedia, the free encyclopedia

    The few I have checked against GPS have been less than 1 MPH too fast at 60 MPH. I'm guessing odometers would be off by the same amount, but don't know that.

  18. #18
    gran jefe
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    when you look at what surveyors use when they need to measure distances, a measuring wheel is basically a cyclometer. the guys who measured the course for the houston marathon used a calibrated bike back when i ran it (well, i only ran the half).

  19. #19
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    Small dot of paint on your tire, roll it and measure between two dots.

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