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  1. #1

    2 Gps Units W/ Diff. Speeds

    Well Yesterday I Took Out My Rxp W/ 3 Hours On It For Some Gps Runs. I Had 2 Different Garmins On Board With Me. One Every Run I Saw 2 Different Max Speed Numbers. How Do I Know Which One Is Accurate. I Had One Peak At 68.0 Mph. I Did Consistent 63-65 Mph Runs. Keep In Mind It Onlly Has 3 Hours On It And The Rpms Arent Quite Up The Full Way Yet. Let Me Know What You Guys Think??? Are These Gps #s Everyone Posts Really That Accurate??


  2. #2
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    Quote Originally Posted by codymouse54321 View Post
    Well Yesterday I Took Out My Rxp W/ 3 Hours On It For Some Gps Runs. I Had 2 Different Garmins On Board With Me. One Every Run I Saw 2 Different Max Speed Numbers. How Do I Know Which One Is Accurate. I Had One Peak At 68.0 Mph. I Did Consistent 63-65 Mph Runs. Keep In Mind It Onlly Has 3 Hours On It And The Rpms Arent Quite Up The Full Way Yet. Let Me Know What You Guys Think??? Are These Gps #s Everyone Posts Really That Accurate??


    WELL, what were the peak numbers on both?

    it all depends on what satellites they hook up with, there can be a SPIKE on one unit and not on the other....

  3. #3
    well the high on the one was 68. besides that i think i saw 65.5 on it.
    and the other one was 64.9. so i figure roughly 65 was the correct gps.


    these were both done sitting on the seat. What is the technique for doing the superman??? Seemed kinda difficult-- water was a little rough too. thanks

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    Quote Originally Posted by codymouse54321 View Post
    well the high on the one was 68. besides that i think i saw 65.5 on it.
    and the other one was 64.9. so i figure roughly 65 was the correct gps.


    these were both done sitting on the seat. What is the technique for doing the superman??? Seemed kinda difficult-- water was a little rough too. thanks



    Arms fully extended + laying as flat as possible + barely looking over the steering = SUPERMAN

    Flipping someone off while doing = Superman w/ STYLE
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  5. #5

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    I have the same problem My E trex is lower than my 605 CX and my Magellan is in between the two there is almost a 3mph difference high to low , Next time Im getting my stalker out !!!!

  6. #6
    I'm kind of a big deal SeanCucf's Avatar
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    I would say the lower one was most accurate if it was choppy.....other one probably was getting bounced around.

  7. #7
    depends on the sampling rate of each gps... the speed is caclulated by the average of values received, so higher sampling rate = more accurate reading. Also remember civilian gps units aren't accurate within a few feet, so for example in the period of 5 seconds you covered 100 ft (actual). GPS A may error short and say you only traveled 98 ft in 5 seconds whereas GPS B may error large and say you traveled 102 ft in 5 seconds. In this case GPS B would display the higher mph.

  8. #8
    I guess the GPS reading is better than the speedo on the craft, but GPS is by no means "accurate."

    Most of the high end speed boat guys refuse to recognize GPS, because like the speedo, it has such a huge variance.

    The only thing recognized is radar or FAT (fully automatic timing).

    Most people don't realize that the GPS system is only accurate to the level of your model. I've seen some GPS that were certified to within 3 CM, but had to be towed around on a truck. High end Trimble receivers that cost on order of $30k are good to a couple of inches, but any of them have to be sitting stationary for a long period of time in order to average out all the variance.

    Moving with the GPS isn't exactly lock solid as far as accurate numbers go.

    I think the only REAL assessment you can do is a change in the instrument you use. That is, if the GPS readout goes up after you mod, then it's significant evidence that the speed of your craft is better. The same with the speedo. Just WHAT your speed is, and any comparison between two different craft would probably have to be done head/head or with the same GPS on the same day (same conditions).

  9. #9
    Quote Originally Posted by jahkneefive View Post
    depends on the sampling rate of each gps... the speed is caclulated by the average of values received, so higher sampling rate = more accurate reading. Also remember civilian gps units aren't accurate within a few feet, so for example in the period of 5 seconds you covered 100 ft (actual). GPS A may error short and say you only traveled 98 ft in 5 seconds whereas GPS B may error large and say you traveled 102 ft in 5 seconds. In this case GPS B would display the higher mph.
    Exactly. Most civilian GPS models are only reliable to within 10 meters. Even the ones we use in the service are not viable enough to locate/benchmark munitions or minefields with them. You still have to use the old surveying methods.

    I think if you used a long average, you'd be pretty close, but just like stated above, the GPS will see variance of the locations and as such, the calculations of the speed can be off quite a bit, so you'd have to ride at WOT and full speed for a very long time in order to average all those highs and lows out to get an accurate number.

    I guess I'd say if you're really interested in getting a good reading, then get a radar gun (or a pitot tube....but that's prolly not in the cards

  10. #10

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    Thats why Im getting My stalker stats radar system out

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