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I have a Garmin 665 GPS. It displays my speed. I have always wondered how accurate the speed display is on a GPS unit? My GPS always reads less than the speedometer on my 2010 Wing. I know the speedometer is not accurate.

Is the GPS indicated speed to be trusted?
 

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The GPS is probably more accurate than the speedometer. GW speedometers usually are 7% or so high and people like me use compensators to adjust if necessary. Also speedo accuracy can be affected by tire size or wear. GPS is not. By the way, odometer accuracy is also affected. Your odo will show higher miles than actual.

I checked my speedometer using a stopwatch and a measured mile. I tweaked the readings using a Yellowbox until the speedo was right on. I could not get the speedo AND the odometer to both be right on at the same time so I chose the speedometer. The odometer is still off by a little under 2%. This means that your miles per gallon calculations will also be high by 2% (or whatever your error rate is).

After I got a GPS I found that it was spot on with my now calibrated speedo.
 

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GPS should be as close as your going to get.
 

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Trusted?

I've found that whenever I enter a speed zones monitored by a stationary radar unit with your speed shown on a large display my GPS is exactly the same.

Good enough for me...
 

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This is a subject that is discussed frequently on here. 2009, '10, and 12 bikes are supposed to be more accurate. I ride an 03 that reads fast but I don't worry about it. I can't see where it's much of a problem. We're aware of it and can calculate our mpg, etc., accordingly.
 

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my 2010 is within 1 MPH of what my GPS reads.
 

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As is my '10 as well.
 

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The GPS speed should be very acurate. The altitude shown by a GPS, without a seperate Altimeter, is however not to be trusted to be acurate. In the ballpark, but not acurate.
Good Luck!
 

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My GPS and speedo read exactly the same, when I'm parked, after that....... you know the rest of the story.....
 

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For 72,000 indicated miles I have checked my speedo/odo with various devices...GPS, measured miles, etc. After many many checks I see that my Wing speedo is exactly 3.5 % higher than actual. So that means I really have only traveled 69,500 miles.
 

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I have a Garmin 665 GPS. It displays my speed. I have always wondered how accurate the speed display is on a GPS unit?
In answer to your question...

First of all, unlike your speedo, your GPS is not telling you your actual "real-time" speed. Over a distance at a steady speed, it will give you an accurate reading, but so far as your speed right now, not so. The GPS can't tell what speed you're traveling..., only how long it takes you to move between two (or more) data points, and calculates your average speed between those points. Dont forget, your GPS doesn't transmit, it only receives..., so once it receives two (or more) data points from the GPS satellites, it can figure out your speed over the previous distance.

In other words, if you're holding a steady speed, the GPS will give you a dead-on reading..., but if your speed is fluctuating up and down (for whatever reason), not so accurate. Any speed the GPS gives you will always be in arrears, while your speedo will be real-time.

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I've found that whenever I enter a speed zones monitored by a stationary radar unit with your speed shown on a large display my GPS is exactly the same.

Good enough for me...
Mine too!

I also found that while most people on this forum with 2010's say their speedometer's are right on, not so with mine. When my rear tire is new it's out approximately 3 miles per hour depending on my speed, when the rear tire is worn and near the end of it's life like it is now it's out 5 to 6 mph. this was confirmed today when I passed through a speed trap with a display board.

I trust my Zumo 550 with in it's working parameters.


Pete
 

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Try the "Speedo Healer"... I did and it can correct your speedo to be DEAD accurate.... I love it... I now know just how fast I'm going and the GPS is confirming that I've been there....if ya know what I mean...

Mountainman
 

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GPS is less accurate on a curve at higher speeds because it will compute point to point distances through the curve. So the faster you are going in a curve, the less accurate the speed measurement. But maybe still as accurate as the speedo.
 

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I have a 2010 level 3. It's speedo reads the same speed as my Garmin 765T. I have checked them both on several speedo-check mile markers and the speed on both seems dead acurate. What is NOT acurate is the odometer on the bike. It consistantly reads about 4% higher miles than the Garmin.

Will a speedo healer correct this without screwing up the speed?

Larry
 

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I have a 2010 level 3. It's speedo reads the same speed as my Garmin 765T. I have checked them both on several speedo-check mile markers and the speed on both seems dead acurate. What is NOT acurate is the odometer on the bike. It consistantly reads about 4% higher miles than the Garmin.
Will a speedo healer correct this without screwing up the speed?

Larry
No
 

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In answer to your question...

First of all, unlike your speedo, your GPS is not telling you your actual "real-time" speed. Over a distance at a steady speed, it will give you an accurate reading, but so far as your speed right now, not so. The GPS can't tell what speed you're traveling..., only how long it takes you to move between two (or more) data points, and calculates your average speed between those points. Dont forget, your GPS doesn't transmit, it only receives..., so once it receives two (or more) data points from the GPS satellites, it can figure out your speed over the previous distance.

In other words, if you're holding a steady speed, the GPS will give you a dead-on reading..., but if your speed is fluctuating up and down (for whatever reason), not so accurate. Any speed the GPS gives you will always be in arrears, while your speedo will be real-time.

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Thanks, best explanation I've heard. In other words, the GPS will tell you what you did, not what you're doing. So, I'm wondering, how far behind is it? If it's a second or less, no big deal, but over that it may be.
 

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I've found that whenever I enter a speed zones monitored by a stationary radar unit with your speed shown on a large display my GPS is exactly the same.

Good enough for me...
While the roadside radar seems to be pretty accurate most of the time, the other day I drove my car through at 37MPH and got a reading of 90MPH.
 

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GPS is less accurate on a curve at higher speeds because it will compute point to point distances through the curve. So the faster you are going in a curve, the less accurate the speed measurement. But maybe still as accurate as the speedo.
I agree and will add that the same error will be there on steep hills. The GPS measures your progress along the surface of the earth from miles in space which will not be the actual path on the ground ( which is what police radar does, LOL ).
 

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My 2010 is spot on with my GArmin Zumo 550.
My 2005 was 4mph off from my Garmin 2720
 
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