GPS vs SPEEDO - Page 3 - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
General V-Strom Discussion Talk about all things V-Strom not limited to just one of the above models

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post #21 of 31 Old 10-22-2019, 11:14 AM
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There are a few speedo correctors on the market. We have one, but there are others.

OydnaR and Stalky Tracker's posts really put the cause in focus. When knowing my speed is important I either add 8% to the speedo or look at my gps.
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post #22 of 31 Old 10-22-2019, 06:20 PM
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The state I live in gives us a 10% fudge because originally our speedos could read high or low by up to 10%, now they can only read high by up to 10%

I put a corrector on my bike because I love to make full use of the 10% fudge and I don't always fit my GPS.

I fitted a MC cruise control to help keep my speeding in check so knowing me speed is spot on when I set my CC enables me to relax when officer plod is about.

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post #23 of 31 Old 10-26-2019, 11:14 AM
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GPS not Geosynchronous

Quote:
Originally Posted by Motorpsychology View Post
The Global Positioning Satellite system is a constellation of satellites orbiting the Earth in a geosynchronous orbit; they stay over the same place as the earth turns, in other words- same as other sat-com satellites. At any given time, a gps unit is reading 8-12 satellites and triangulating your location to within a meter or two, and your device compensates for calculation time.
US-market speedometers in the late seventies-early eighties were mostly quite accurate, as in those days the infinitely wise USDOT mandated all speedometers display no more than 85mph,and the readout was calibrated much more accurately. Apparently, the thinking was that if you don't know how much over 85 you were going, you wouldn't attempt to. Anyway, my '80 Kawasaki KZ750 speedo is right on with a newish front tire (pickup gear drive cable-driven from front wheel) checked with a first-gen Garmin e-Trex
I think the manufacturers err on the side of caution to allow for alternative tire profiles/sizes.
Most of what you mention is correct except about the orbit. GPS satellites are not in geosynchronous orbit. Geosynchronous satellites orbit the Earth at approximately 22,000 miles while a GPS satellite is approximately 12,500 miles and complete 2 orbits of the Earth each day. You need at least 3 satellites to get the general location of you position but more satellites are better and usually 5 satellites is the minimum to get an accurate position of you location.

Generally a hand held GPS receiver will track 8 to 12 satellites. Satellites that are low on the horizon will not be as accurate because of the effects of obstacles on the surface of the Earth that affects the GPS signal from the satellite and the effects of a greater distance the GPS signal has to travel through the atmosphere.

There is a satellite that is in geosynchronous orbit that is used with GPS satellites. It is called WAAS, Wide Area Augmentation System and is used/being developed with the FAA. It is currently only available in the United States and Canada and Mexico.

Last edited by AZ-Stromer; 11-11-2019 at 03:11 PM.
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post #24 of 31 Old 10-26-2019, 02:28 PM
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I had a KZ1100 with one of those 85mph speedos, buried the needle on a regular basis. If it wasn't electronic I'm sure I would have broken it.
As for the Glee, with an 8% error, I just figure 5%, which is easy math to do without pencil and paper. That way I'm close, but still have a small safety margin for legality.
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post #25 of 31 Old 10-27-2019, 10:29 AM
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I've noticed that GPS displays of speed are somewhat slow to respond to actual changes in speed. I assume that the speed is calculated by measuring the distance and time the bike travels between GPS calculated locations. These measurements of distance and time are also affected by land forms and vegetation blocking some satellites; if traveling under heavy tree leaf cover, a GPS is just guessing at speed. But a bike speedometer (accurate or not) seems to respond instantly to changes in speed.

Lots of words to say the GPS speed display is close to accurate over some short period of time (if the GPS is getting good satellite signals), but not on an instant basis.

Now riding a Honda CB500x; thinking about buying a 650 Vstrom.
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post #26 of 31 Old 10-29-2019, 09:06 AM
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Question

On this same topic, but with variance, has anyone considered the MPG implications.

I just came back from a 4,000m trip and was working out my MPG.

Considering I also noted the large error on the Wee speedo I then wondered if this was also the case on the odometer?

If so, it makes a mockery of the MPG figures I'm getting - if they are also 10% 'worse' then they're not so great really.

Any thoughts?

Previously I've had a cycle speedo on my bikes which are pretty dead on, fitting one would confirm (or otherwise) the odometer accuracy I guess - anyone done this?

IF the odometer is 10% then any MPG is out - bit of a dieselgate situation far as I can see

By the way - not that it matters on above, but does on figures next - I'm in UK - gallons etc and worked out 57MPG. If its actually nearer 50 I'd consider that pretty poor! (K9 2009)
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post #27 of 31 Old 10-29-2019, 09:37 AM
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Quote:
Originally Posted by Fritz View Post

IF the odometer is 10% then any MPG is out - bit of a dieselgate situation far as I can see
don't start a rumor, the odometers are pretty much right on

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post #28 of 31 Old 10-29-2019, 11:10 AM
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Quote:
Originally Posted by Fritz View Post
On this same topic, but with variance, has anyone considered the MPG implications.

IF the odometer is 10% then any MPG is out - bit of a dieselgate situation far as I can see
: (K9 2009)
Federal regulation require the odometer to be accurate, but realize that the odometer is calculated to the diameter of the tires so any change to the tires cause an accuracy error. Not just different size tires but Including worn tires.

Accuracy depends on the manufacture not cheating. Some years ago Honda got caught claiming better mileage then actual. The odometer was accurate they just lied on window sticker of new cars.
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post #29 of 31 Old 10-29-2019, 11:34 AM
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Yeah I wasn't sure whether the internals of the speedo are different between odometer and speedometer sides...if they are one can be set to under-read (speedo) while other is accurate (odometer).

If one gear did both, then if speedo is wrong then so to must the odometer.

That's what I wanted to know.

Don't know the internal workings of the instrument...and don't really want to investigate
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post #30 of 31 Old 10-29-2019, 12:15 PM
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My speedo was showing about +8-9% than my actual speed. With all these speed cameras in NYC, I thought it was best to know the actual I was going so I got the SpeedoDRD. Installation and set up was a breeze.
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