posted April 23, 2002 01:18 PM
Got me a new Etrex!! Picked up a new Garmin Etrex GPS from Fry's. On sale for $79, so I said fuck it! Have been finding out a lot about my speedo error. At an indicated 192 mph, the gps said I attained 174 mph actual. That was a couple nights ago. Yesterday I got 93.4 mph actual while cruising at 100mph on the speedo. I don't know what the speedo said last night when I was coming home, but the gps told me max speed 179 mph. I figure 9.375% inaccuracy at the 192 reading would equate to a speedo reading of about 198 last night when I attained the actual 179 mph. I can't wait to get a new tire, get a new clutch, lube up the chain, change the air filters and see what this thing will do WFO on an empty straightaway. I have over 16k on it now...all original shit except for the Yosh slip-on thanks to Dudedad.
What have you guys seen on your GPSs? List your mods along with your MPH if you've done it.
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posted April 23, 2002 02:09 PM
That looks like about a 10% error Which sounds about right and is pretty common. I've read the same with stock and +1 on back with my old Garmin GPSIII. This is backed up with my Sigma Targa.
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There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
posted April 23, 2002 05:09 PM
Hawk, is this the *newest* 12 you've had??? You couldnt have had that bike more than a year now...could you???
You are a riding mofo on that bike!
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posted April 24, 2002 11:39 AM
Dude! Living down in Southern California has me riding my bike ALL the time. Yes...it's my new ZX-12R. [chuckles] I've had it just over 10 months. lol Seemed like yesterday that I just changed my rear tire. I probably ride 75 miles a day during the week. On the weekend, I go out riding with the fellas and rack on another 200-300 miles. Whew! Sure is fun though!!
posted April 24, 2002 02:55 PM
Edited By: TedG on 24 Apr 2002 15:59
The resolution on those things is about 10 seconds, which means you must hold that speed for at least that amount of time, otherwise it took a reading while you were accelerating or decelerating. Sometimes you can get lucky and it will take a reading while you are at the desired speed, so if you hold it for 1 second you have a 1 in 10 chance of getting that reading. And even that will read slow because of the delta speed during read intervals. The Uniden GPSRD has a 1 second resolution and makes it easier to get an accurate reading.
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Ted
2000 Green ZX12 sold
The fast color!!
Green 2005 ZX10R
2009 Concours Black ABS
posted April 24, 2002 08:08 PM
My eTrex updates once/second. Velocity accuracy = 0.1 knot. According to the specs sheet anyway.
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NESBA #209
posted April 24, 2002 09:14 PM
Mine is once every 10 seconds. Must be an older one. If they update every second then all is good.
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Ted
2000 Green ZX12 sold
The fast color!!
Green 2005 ZX10R
2009 Concours Black ABS
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posted April 24, 2002 10:03 PM
Sampling rate 10 seconds? Having had an old GPSIII on my bikes for almost five years, I'd tend to believe that a 10 second refresh rate for Garmin products is a tad inaccurate and politely beg to differ.
Even though the GPSIII & III Plus are lacking WAAS capability, their refresh rate and accuracy are far better then a rate of once every 10 seconds. Naturally, antenna position/location and atmospheric conditions will have an effect on the rate and it's accuracy. Just as the signal strength and the number of satellites that are locked in at the time.
From my personal experience of having my GPS located on top of my tank bag, I would say that it's ability to accurately reflect both current and top speeds, are generally in the one second range. Keeping in mind, at 150 mph, you will cover 220.5 feet in that same one second period. Also, aspects such as rate of acceleration (and deceleration) must be figured into the mix. At a one second sampling rate, the current and top speed numbers could easily be off to a small degree.
This is why I always confirm my GPS numbers against my Sigma Targa. Since the Sigma is measuring the number of rotations of the front wheel, environmental aspects have little to no effect on it's readings. The Sigma measures current speed in the hundredths of a MPH and top speed in tenths. Since I use a "two magnet" set up for the system's pick up sensor, the sampling rate at that same 150 MPH would be 76 times per second (28.5 per second at 60 MPH).
Front wheel tire growth, tire pressure changes and other aspects that might result in the front tire's circumference changing, is a factor that I will accept. As minimal as it is. With that being the case, I can comfortably state that the Sigma is easily within .5~1.0 MPH in it's accuracy. As for how the Sigma's top speed numbers vary from that of my GPSIII, about the biggest deviation I seen between the two has generally been less the 1.0 MPH. The worst I've ever seen in over 100,000 miles of readings is 1.2 MPH.
I don't believe the E Trex is WAAS capable either, but I'm sure that it's technology of processing an accurate speed from it's sampling is at least equal if not better then my old GPSIII. That even with the fact that my GPSIII has an external antenna. When it comes to GPS accuracy, it's location and location. On the bike and in relationship to the satellites (signal strength and number).
Just my humble opinion... for what little it's worth.
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There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
posted April 25, 2002 08:57 AM
High speed runs My biggest problem results from having the eTrex mounted to the triple clamp. When making high speed runs I have my chin on the tank and I tend to obscure the unit's view of the satellites. More than once I have sat up and noticed the eTrex was trying to regain a fix. That pretty much negates the run as far as speed recordings. Still, for the money, it's a damn fun toy.
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If you aren't an AMA member, you're part of the problem.
NESBA #209
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posted April 23, 2002 01:18 PM
Edited By: 
posted April 24, 2002 10:03 PM
