kurt
Well-known member
When GPS indicated 70 mph, my '08 speedometer shows 75.
08 | GPS Speed vs Speedometer
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SacramentoMike
Not Safe For Work
My GPS reading is right in sync with my speedo on my 05. But just to be sure, I made a mark on the road at mile marker one on a nearby state highway, and another mark at mile marker 75. I was going to ride for an hour at 75 m.p.h. and see where I ended up, and it would have worked, too, if I hadn't had to stop for gas.
RTSR1/FJR
Gort - Klaatu barada nikto!
Mine's an '03 Gen I, not a Gen II. GPS says 70, speedo says 70. I guess that the diff between a speed sensor and pulling the speed from the ABS. My R1 is 12% off, but it is -1 on the front sprocket though. Corrected with a Speed Healer!
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RonBB
Well-known member
Nope no affiliation with Garmin other than owning two garmin GPS units. Am a retired EE & was in the construction/heavy Industry field's. Also a pilot & have used GPS since it's inception.
PS. If I worked for Garmin I would not have included a maximum speed feature in the Zumo that could not be disabled.
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Brody
Well-known member
75-70=5
5/70=.0714=7%
so at an indicated speedo of 30mph........................for ex.
30 X .07=2.1
your GPS will read 2mph lower or 28 mph
saread
Well-known member
I would be careful about relying on GPS speed readings. The level of accuracy of a consumer grade GPS unit with an uncorrected signal is on the order of 10 meters. Or, picture yourself inside a 60 ft. diameter circle, and the GPS is telling you that you're somewhere inside that circle. With a signal corrected in real time useing one of several correction signals (WAAS, Coast Guard, commercial vendor, base station, etc.) this improves to about 3 meters. The level of accuracy depends on how many satellites the GPS is tracking (more is better), the location of the satellites in relation to the horizon (higher is better), and the type of day (clear is better than cloudy or hazy). The signal from the satellites is extremely weak, and when signal is dispersed through the atmosphere or clouds, it slows down (trust me, it does). This screws up the timing calculations and introduces error to the position calc. (hence the need for a corrective signal). GPS units cannot calculate continuously, they take a reading at a point in time and then calculate the position. Typically, readings are taken every second. So, my point is that there is a certain amount of error in GPS readings. Now, assuming that the error is constant, and speed is calculated using average time between positions, we can assume that the speed shown on the GPS is reasonably accurate. However, it's a pretty big assumption that the error is constant. All this being said, I must say that I've had no reason to doubt the speed readings on my Garmin, I just don't know to what degree I can actually rely on them.
brazos parker
What??
Interesting.
However, I, for one, hardly ever look for speed on the GPS. It's so much easier to glance at the speedo to get my speed...much quicker and safer that way. In the event I don't pay attention and/or rely on either one, I figure the local po po will be more than willing to tell me my exact speed as measured by his down to earth instant-on lidar!
In my post above (and others), I was only responding to the original question w/ my experience comparing the speedo and GPS.
YMMV and FWIW.
However, I, for one, hardly ever look for speed on the GPS. It's so much easier to glance at the speedo to get my speed...much quicker and safer that way. In the event I don't pay attention and/or rely on either one, I figure the local po po will be more than willing to tell me my exact speed as measured by his down to earth instant-on lidar!
In my post above (and others), I was only responding to the original question w/ my experience comparing the speedo and GPS.
YMMV and FWIW.
Do you work for Garmin in K.C. ?
Nope no affiliation with Garmin other than owning two garmin GPS units. Am a retired EE & was in the construction/heavy Industry field's. Also a pilot & have used GPS since it's inception.
PS. If I worked for Garmin I would not have included a maximum speed feature in the Zumo that could not be disabled.
I've wondered if the police are generally aware of the top speed storage feature. Just in case, I took mine flying one day. If the cop asks for the top speed, I'll punch a few buttons on the Zumo and say "601 miles per hour sir. Do you take American Express?"
Nope no affiliation with Garmin other than owning two garmin GPS units. Am a retired EE & was in the construction/heavy Industry field's. Also a pilot & have used GPS since it's inception.
PS. If I worked for Garmin I would not have included a maximum speed feature in the Zumo that could not be disabled.
I've wondered if the police are generally aware of the top speed storage feature. Just in case, I took mine flying one day. If the cop asks for the top speed, I'll punch a few buttons on the Zumo and say "601 miles per hour sir. Do you take American Express?"
canyonman
Well-known member
Do you work for Garmin in K.C. ?Nope no affiliation with Garmin other than owning two garmin GPS units. Am a retired EE & was in the construction/heavy Industry field's. Also a pilot & have used GPS since it's inception.
PS. If I worked for Garmin I would not have included a maximum speed feature in the Zumo that could not be disabled.
I've wondered if the police are generally aware of the top speed storage feature. Just in case, I took mine flying one day. If the cop asks for the top speed, I'll punch a few buttons on the Zumo and say "601 miles per hour sir. Do you take American Express?"
+1 mine is showing 581mph
magellen and zumo both show my fjr reads high. the faster I go the larger the difference (a percentage).
However both have shown my HD to be dead on.
Using the zumo last summer on a mixed group ride all three asian bikes (including my 07fjr) were showing higher speedo readings and both harleys were showing what the zumo was showing. this was crossing southern kansas and southern colorado on a perfectly clear day.
Rondo777
Well-known member
Zumo here too, mine is dead on with my car 2007 Toyota FJ Cruiser but off by about 4 miles per hour at around 70. My buddy rides on 08 R1 and 4 mph off from his too at 70.
usetobeharley
Member
Without any doubt, the GPS indicated speed is accurate. Much much more accurate than a speedometer.
HaulinAshe
Well-known member
I can produce extended situations where the Garmin Zumo GPS reads something like 22 mph and the bike speedo reads 45 mph. You simply have to haul ass around some very tight NC mountain twisties!
GPS readings in a straight line are nearly dead-accurate. My 07 speedo runs 7-10% over. Makes gas mileage look great when it's really NOT. Makes the bike look much older than it really is!
GPS readings in a straight line are nearly dead-accurate. My 07 speedo runs 7-10% over. Makes gas mileage look great when it's really NOT. Makes the bike look much older than it really is!
bramfrank
BramFrank
Actually, only the postion information is used to calculate speed for the tracklog.
Speed vectors are a doppler function of the decoded satellite signal and are 'real time' from the perspective of each calculation.
Most consumer GPS units provide position information once per second. tracklog data is only updated when there is a 'significant deviation' from the previous vector - so tracklog speed is the AVERAGE speed between two points ina straight line.
As such, given that the tracklog tends to 'cut the corners a bit', the calculated speeds are actually a bit low - but don't tell the two judges who accepted my GPS data as evidence to get out of performance awards.
My 276c is sitting at 1376 kph (compliments of a glitch) which completely freaked out a a police officer who thought he would be a smartass. Zumo 550 says something like 497 mph - compliments of American Airlines.
Note that it simply doesn't matter what the top speed reading of your unit says - they have to observe you doing the deed to ticket you for it.
Speed vectors are a doppler function of the decoded satellite signal and are 'real time' from the perspective of each calculation.
Most consumer GPS units provide position information once per second. tracklog data is only updated when there is a 'significant deviation' from the previous vector - so tracklog speed is the AVERAGE speed between two points ina straight line.
As such, given that the tracklog tends to 'cut the corners a bit', the calculated speeds are actually a bit low - but don't tell the two judges who accepted my GPS data as evidence to get out of performance awards.
My 276c is sitting at 1376 kph (compliments of a glitch) which completely freaked out a a police officer who thought he would be a smartass. Zumo 550 says something like 497 mph - compliments of American Airlines.
Note that it simply doesn't matter what the top speed reading of your unit says - they have to observe you doing the deed to ticket you for it.
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