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Discussion Starter · #1 ·

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Virtually all speedometers are inaccurate. I've seen many reports like yours that say there is a discrepancy between GPS and speedo readings. My question is how accurate is the GPS? I think that the only way you will find out how far out your speedo readings are is with a measured, true, mile.
I like the idea of having a fairly accurate speedometer for the legality aspect of things, but mileage it really isn't that much of a concern, I ride for the joy of it. There aren't many bikes that can best my diesel Jetta for fuel economy, an honest 64mpg (imperial).

Dave
 

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Discussion Starter · #3 ·
Well, my GPS and my truck are V-E-R-Y close. so I just assume the Scoot is the inaccurate one. I like to know my actual MPG so when I brag about it, I'm not too far off center !

DougThompson
Pikeville, Kentucky
 

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you read my mind...... :eek:
i was gonna start a thread on this very topic today !

i have noticed some big discrepancies between the gps and the speedo.

i have not checked the mileage figures yet, but i will do so this weekend, as im off on a 400km round trip to go see my parents.

i will post the results when i get back.

jason
 

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I have seen the GPS error quite a bit, in which case always results in less miles than actually traveled. I am sure the speedo is a bit high, but that is truly excessive.
 

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You meant Odometer... :lol: I'll check it out this afternoon. My car is right on the money and I happened to have driven scooter today. It's supposed to storm real bad this afternoon so hopefully I won't get any tire spinnig to throw her off. :p
 

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This morning when I left work, I reset my trip odometer. My normal route home takes me south on US-1 to I-95 north, to Ashland, where I get back onto Rt. 1 north again.

This morning because of heavy fog, I took Rt-1 through Richmond to Ashland. Not the exact same route, but Rt-1 so closely parallels I-95 that for all intents and purposes it can be said to be the same distance.

When checking the distance in my car, it comes up to 78 miles. This morning the odometer on my Majesty showed 76 miles and some change. Add to that the mile and a half, 2 miles or so I have to go south to get on I-95 north, and I'm reasonably convinced the odometer on mine is correct. The next time I go to work, I'll try to remember to check it on the exact same route.

The speedometer I have no idea about.
 

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Discussion Starter · #8 ·
Well, I will do some more test with mine - maybe today, as it's supposed to be in the fifties. But my GPS has been checked against the odometer of my '01 Dodge Diesel pickup and was nearly right-on.

The error I recorded is substantial and if I find I was in error, I will post here.

Thanks to all for all the feedback.

DougThompson
Pikeville, Kentucky
 

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just got back from my trip.

here are some interesting results.....

the trip to my parents place...
1 % over on a 171 km trip

odometer reads 173.3 km
actual (gps) reads 171.5 km



the trip home (slightly different route home)

1.3 % error on 178.9 km trip

odometer reads 181.2 km
actual (gps) reads 178.9 km



the differences between the trip there and back might be put down to the fact that it was wet and rainy in the way home with complete cloud cover.
this might have added to any small error with the gps's accuracy. im not sure, but even with the differences, it's too small an amount to worry about (imho)

however, i have noted some very incorrect speed readings from the speedo on the maj. bellow are the results and these figures are the same no matter what the weather conditions, the error percentage is the same every time.

Indicated Speed.............Actual Speed

60 km/h..............................57 km/h
70 km/h..............................66 km/h
80 km/h..............................75 km/h
90 km/h..............................85 km/h
100 km/h............................92 km/h
110 km/h...........................102 km/h
120 km/h...........................111 km/h
130 km/h...........................120 km/h
140 km/h...........................130 km/h

so the speedo consistantly reads under at All road speeds.
i wonder if it can be re calibrated to read correctly ?

jason
 

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I have seen discussion on another board, I'm not sure which one right now, that indicate that others have noticed that the speedometer seems to read about 10% low, but that the odometer seems to be right on.

I have no idea if it can be recalibrated.
 

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Just last night my husband and I were laughing about the error in his GPS. We were sitting at about 10 ft elevation and the GPS said we were -274 feet. (We were playing submarine!)

There is a substantial margin of error for the GPS units. Impossible you say?? Well, the ultimate accuracy of GPS is determined by the sum of several sources of error:
1. Atmospheric Conditions is the most common and can cause as much as a 30 meter error. For the metric-challenged, that's 98 feet!!! The ionosphere and troposphere both refract the GPS signals. This causes the speed of the GPS signal in the ionosphere and troposphere to be different from the speed of the GPS signal in space. Therefore, the distance calculated from "Signal Speed x Time" will be different for the portion of the GPS signal path that passes through the ionosphere and troposphere and for the portion that passes through space.

2. Ephemeris Errors/Clock Drift/Measurement Noise. Ephemeris is a fancy term for orbital position. The error (correction) data for any given satellite may not exactly model the true satellite motion or the exact rate of clock drift for the satellite. Distortion of the signal by measurement noise can further increase positional error. The disparity in ephemeris data can introduce 1-5 meters of positional error, clock drift disparity can introduce 0-1.5 meters of positional error and measurement noise can introduce 0-10 meters of positional error. Here's up to another 16.5 meters (54+ feet)

3. Selective Availability. Selective Availability (SA) is the intentional alteration of the time and positional signal by the Department of Defense. SA can introduce 0-70 meters of positional error. Fortunately, positional errors caused by SA can be removed by differential correction in high-end units. But for us, add in up to another 70 meters (229 feet). (Although SA is now turned off, there has been recent discussion of turning it back on.)

4. Multipath. A GPS signal bouncing off a reflective surface prior to reaching the GPS receiver antenna is referred to as multipath. Because it is difficult to completely correct multipath error, even in high precision GPS units, multipath error is a serious concern to the GPS user. Fortunately this is only up to 1 meter (3+ feet)

Leaving out the error for SA, this gives us a total of as much as 41 meters (155 feet) of error in the GPS unit!!! Kind of makes the error in our Majesty odometers look benign.

Bottom Line: The GPS units we can affordably purchase are not precision instruments. They are like a garden variety "bathroom scale" is to precision scales. They'll get you into the ball park, but probably not on home plate!

GPS receiver prices range from: Hand-held, lower precision receivers for waypoint navigation and recreational use $100 - $500; moderate precision units for GIS mapping $1,000 - $5,000 (1-5 meters with differential correction); moderately high precision units (sub-meter with differential correction) for GIS mapping $5,000 - $10,000; high precision survey grade receivers (cm and mm accuracy) $5,000 - $30,000.

These ultra-precise GPS units use a terrestrial (earth bound) beacon to correct for error. This is a subscription service, but probably not worth it for our use. Look at the 18-wheelers some time. Some of them have a little white dome on the top of the cab. This is a precision GPS antenna and is usually installed by the owner to be able to track the truck. Sears has them installed on many of their service trucks to track the technicians!! (Make sure they don't goof off). These high-precision GPS units also were used in the recovery operations of the Shuttle Columbia to allow the searchers to accurately mark the position of the debris for the recovery personnel.

Sorry for the long post, but thought you'd like to know your speedometers and odometers probably aren't as inaccurate as you think.
 

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as i stated, my odo seems to in the ball park, it's the speedo that im not so sure about.

the two trips average out to less than 1.15 % different to what my gps read. and the speedo always differs from the gps by the same %. ie
an indicated speed of 70 km/h will always show as 66 km/h on my gps.
and an indicated speed of 100 km/h will always show as 92 km/h on the gps.

this figure does not vary with weather conditions at all. also my gps reports positional accuracy (no idea how) and it's usually down to under 10 meters (30 feet) and in most cases about 4 meters.

here in oz, we dont have the waas system either.

jason
 

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GPS speedometer readings are generally considered to be accurate. I used to play with one (an Eagle) in my truck a few years ago, and it was always right on what my truck speedometer read. Among the high performance bass boat community, GPS is considered the most accurate speed reading over water you can get, even more accurate than police type radar readings. Even having said that, the only accurate speed reading is two timed passes over a measured mile, averaged.

The feelings on the other board was that Yamaha has the speedometer off delibertaly for whatever reason, and the odometer reading correctly to maint purpose. I'll see if I can't find the other posting and post a link here.

http://www.maxi-scoots.com/postnuke...edometer&sid=0f66bf04c42bad92660d8b42912202f6
 

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Discussion Starter · #14 ·
I would think that if the odometer is off, the speedometer is off. Doesn't one gear or sensor drive them both ?

The error on the Majesty odometer would make one think they are getting better fuel economy than they actually are. That would be one reason Yamaha would delibertly have it read in error.

Also, given the error I recorded on mine, it would be out of warranty much sooner wouldn't it ? Or how is the warranty worded ? One year or 12,000 miles? Or just one year ? I don't remember seeing any mileage on the warranty but I am sure it was a year.

Of course, when I'm going 65 MPH on Majesty's speedometer, I'm actually going around 61. THAT helps me keep her down below Mach 1.

I don't mean to be overly critical but if my automobile odometer was off that much, I would be raising heck.

Wouldn't you ?

DougThompson
Pikeville, Kentucky
 

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They are not necessarily related, for example, on a cable driven system where the cable from the front wheel connects to the speedometer / odometer unit, but after that the mechanics then split, one taking the path of the active needle and the other driving the mileage gears ... and there is room for error. As for electronic systems, I am sure the same could apply, but since I have never broken it down to see how it actually works, I cant say for sure. Logic would dictate that for the electronic versions, they would match, but it seems as if they do not.
 

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Discussion Starter · #16 ·
:oops: I sure opened a can of worms with my GPS post, but I thank each of you for your info. I have learned a lot. Blexcroid and Texas Cycle, I am about ready to declare that I really don't need to know EXACTLY how fast I'm going. It's not important anyway, and does it really matter how many miles I can travel on a gallon of gas ? As long as I can pay for it, I'll buy it regardless ! It's like trying to get another half horsepower from your engine or shave a half second in your quarter mile.

I have noticed my GPS isn't always that close, but like you said, it gets me in the ball park. I never considered heavy weather would affect GPS performance, but I can understand now how it would.

I worked for the CSX Rail Road for 23.5 years and watched them upgrade their fleet of locomotives with GPS. Of course, all the rail roads have them now.

The big wiggs in Jacksonville Florida, which is CSX's headquarters, monitor each locomotive in the entire system. "How long has this locomotive been sitting in idle? Was that a red signal you just rolled through ? Wait a minuite, I see you've been speeding a little."

This technology is absolutely mind blowing to me. Orwell would roll over if he knew how far we have "progressed" !

Again, Thanks !

DougThompson
Pikeville, Kentucky
 

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Blexcroid, correct me if I am wrong, but SA has been switched off for some years now. Also, your example of an incorrect elevation report is not too disturbing. The geometry inherent in gps orbits makes elevation readings much less accurate than lat and long.

CB, there are plenty of ways of calibrating speeds. The measured mile is one of them.

I still wish I could afford a good gps!
 

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as for the earlier question about warranty, we here in oz get a two year unlimited kilometer warranty !

you guys in the us only get 1 year ? that sucks.....

jason.
 

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gpsnut2003 said:
as for the earlier question about warranty, we here in oz get a two year unlimited kilometer warranty ! you guys in the us only get 1 year ? that sucks.....jason.
It's 1 year/unlimited distance for Canada. In Manitoba, the riding season typically starts in April and ends early in November, so I will have about 7 months worth of riding before the warranty is up.
 

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thats not really good at all !

i will have somewhere near 40,000 km on mine before the warranty is up.

we here in oz, average about 20,000 km per year. so far im right on target too :lol:

i got the maj at the end of sept 05, and have done 7300 km so far ! first major service (10,000km) should be about march (6 months old)

jason.
 
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