View Full Version : Speedo\GPS accuracy
Redkite2
10-06-2006, 09:49 PM
How reliable is the road speed indicated by the GPS? When my speedo reads 145 Kph, the GPS reads 122. Thats a big difference. Cheers, Stu
crust
10-06-2006, 09:56 PM
GPS is not 100%
neither is a bikes speedo, can overead up to 10%
have you changed gearing?
:) Crust
Redkite2
10-06-2006, 10:23 PM
No, it's standard
crust
10-06-2006, 11:13 PM
could be down to tyre profile or even pressure
:) Crust
How reliable is the road speed indicated by the GPS? When my speedo reads 145 Kph, the GPS reads 122. Thats a big difference. Cheers, Stu
My Garmin GPS is accurate to +/-0.05metres per second - which is much better than a speedo (I let you do the arithmetic!) At an indicated 82 mph on my BMW GS the GPS reads 80mph - this is pretty good - most speedometers are widely optimistic and read about 10% high or even worse.
Redkite2
11-06-2006, 07:40 AM
Crust: tyre pressures are good, bikes only done 1500 Km's.
Will: Sounds good, but how do you know that the GPS is accurate ?
There seem to be just as many that say nay as say yea>
Cheers, Stu
Crust: tyre pressures are good, bikes only done 1500 Km's.
Will: Sounds good, but how do you know that the GPS is accurate ?
There seem to be just as many that say nay as say yea>
GPS is definatly more accurate than your speedo. You can be pretty sure the GPS is 'accurate'. Find a website and read about the timing problems and conditions that the satellites and their atomic clocks face and you'll be pretty convinced. Also, it takes four of these satellites to work out you position (and speed), so the error is very small indeed.
Crust: tyre pressures are good, bikes only done 1500 Km's.
Will: Sounds good, but how do you know that the GPS is accurate ?
There seem to be just as many that say nay as say yea>
Cheers, Stu
Because that is the specification for the instrument - I have no reason to believe that Garmin are 'fibbing'. The accuracy probably has more to do with the fundamentals of satellite GPS rather than the receiver itself and I am guessing, but as long as the receiver has an accurate timebase (crystal oscillator - which is easy and cheap to produce) then it will be very accurate. More research required in order to confirm this though!
Roberto
11-06-2006, 10:08 PM
most bikes I hve had have been around 5% out, gearing changes put them total out of whack..
fitted one of these to my last bike after changing the front sprocket.
http://www.speedohealer.com/eng/intro.htm
Bodybag
12-06-2006, 11:26 AM
Is my bike the only one where the speeod runs from the front wheel? Never seem to have a problem with mine at all. Have to admit though that I've lost 6mph off the book speed of my S4 by changing the rear sprocket for a larger one.
As for GPS it is very accurate and as Pugi said. It takes (at least) 4 to work out your speed. My Garmin will run off up to 12 satellites at once for position, direction and speed calculations. Makes it almost infallible. :)
Is my bike the only one where the speeod runs from the front wheel? Never seem to have a problem with mine at all. Have to admit though that I've lost 6mph off the book speed of my S4 by changing the rear sprocket for a larger one.
No, I have that too. Neither I understand how gear changing may affect the speedo. Are the rest of yours measured differently?
No, I have that too. Neither I understand how gear changing may affect the speedo. Are the rest of yours measured differently?
Garmin eTrex says my speedo over-reads by 8-10%, which sounds about right to me.
Roberto
12-06-2006, 02:53 PM
No, I have that too. Neither I understand how gear changing may affect the speedo. Are the rest of yours measured differently?
I have been a kawi man till now, well still am till Wednesday, allot of jap I4's have a sensor on the front sprocket, so gear changes front or back screw your speedo a little.
not sure about my up and coming bike, but canny if its on the front wheel.
1 duc very low mileage been wheelied loads :chuckle:
Tonio600
12-06-2006, 03:23 PM
have you changed gearing?
Now you need to explain me how that could spoil the speedo measure :)
Tonio600
12-06-2006, 03:26 PM
I have been a kawi man till now, well still am till Wednesday, allot of jap I4's have a sensor on the front sprocket, so gear changes front or back screw your speedo a little.
not sure about my up and coming bike, but canny if its on the front wheel.
1 duc very low mileage been wheelied loads :chuckle:
Thanks for the explaination... But I don't think any Duc is working like this. Either it's driven by the speedo drive on the front wheel either it's a magnetic count of the bolt heads on the rear sprocket. But once again I'm not sure, I better say nothing :) :)
Early Monsters: mechanical speedo, front wheel driven.
Later ones: Electrical as described by Tonio.
Not sure when the switch occurred though. 2001/2002 I think.
Early Monsters: mechanical speedo, fromt wheel driven.
Later ones: Electrical as described by Tonio.
Not sure when the switch occurred though.
Finally sorted out. Thanks both of you.
Still 100% sure the GPS is more accurate either way though.
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