My Garmin 2610 reads 65 mph when my ST1100 speedometer reads 60 mph. Seems like a pretty big difference. Which should I believe? I tend to believe the Garmin.
Which MPH is acurate - GPS or Speedo?
- Thread starter RideOn
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Papa Ritch
Ritch Davis
That about like my ST 13 - 5 MPH off from my GPS, also my watch on mile posts marker. 
Garmin. Absolutely. Even if your speedo was accurate (which it isn't), there would be variations in the condition of your tires (wear and inflation) that would throw the accuracy off.
On the other hand, a GPS will only sample your location at fixed intervals, so your wheels could travel more distance than the GPS would see. If you look at a GPS track of tight twisties, lt looks like a zig-zag and you don't see the radius of the turns.
GPS is also subject to error when it comes to speed readings. It's not that uncommon to see a top speed reading over 100 when you know you haven't gone a bit over 99.
Mandel
On the other hand, a GPS will only sample your location at fixed intervals, so your wheels could travel more distance than the GPS would see. If you look at a GPS track of tight twisties, lt looks like a zig-zag and you don't see the radius of the turns.
GPS is also subject to error when it comes to speed readings. It's not that uncommon to see a top speed reading over 100 when you know you haven't gone a bit over 99.
Mandel
I experianced today exactly what Mandel is stating ocurr's. I saw my max speed was 134 MPH. I know I was never near that today Nor any other day for that matter. I always reset the max speed to avoid an inquisitive 
oliceST: so it must have lost it's reference at one point today.
My riding buddie stated exactly what Mandel did.
I do take into consideration that the ST speedo is about 5 % off the actual speed. ( slower than actual speed )
Joe
oliceST: so it must have lost it's reference at one point today.My riding buddie stated exactly what Mandel did.
I do take into consideration that the ST speedo is about 5 % off the actual speed. ( slower than actual speed )
Joe
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I'd be keen to hear others experiences with the GPS/Speedo difference.
On my M109R the speedo is about 10% higher than actual..I know with other vehicles I have had the speedos are usually erring high from the manufacturer.
If ST's is reading low..I'd like to have that confirmed as I drive right on the limit of "ticketing"!
On my M109R the speedo is about 10% higher than actual..I know with other vehicles I have had the speedos are usually erring high from the manufacturer.
If ST's is reading low..I'd like to have that confirmed as I drive right on the limit of "ticketing"!
FJRHank
"Scooter Pimp"
Most people (all?) indicate the speedo reads higher then actual. Think about all the law suits Honda would face if it was lower then actual?
Something doesn't seem right there...
Regards,
Something doesn't seem right there...
Regards,
When you're moving, the GPS is constantly running speed calculations based on its most recent info from the satellites, and if you're in an area where you're not getting good steady satellite data, the calculations can get laughably wrong, and the max speed memory will capture them.I experianced today exactly what Mandel is stating ocurr's. I saw my max speed was 134 MPH. I know I was never near that today Nor any other day for that matter. I always reset the max speed to avoid an inquisitive
My riding buddie stated exactly what Mandel did.
I do take into consideration that the ST speedo is about 5 % off the actual speed. ( slower than actual speed )
Joe
When you're making a long steady run across open country on a straight road, the speed your GPS displays will be very accurate. That's the time to compare it to your speedo. My GPS shows 46 when my speedo says I'm doing 50. If the error is linear, that extrapolates to 92 on the GPS when 100 shows on the speedo - an 8% error.
I will leave it up to someone who has done this at 100 to verify my estimate. I don't see triple digits too often.
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At a tad over 150 indicated my Garmin eMap and later model Garmin 2730 captured 141 as the high speed.
As has been stated GPS units average speed over time. D/T = S. The Garmins update about once per second. If it gets one of those 200 or 300 mph errors from a bad position it goes into the pot to be averaged with all the others that are generally within .01% of dead-on. So if you ride any distance at all with updates 3600 times an hour those spurious high (and low - on occasion I have seen my 2730 read low) numbers don't impact the average very much.
GPS is very accurate. It wasn't always so with early single channel multiplexing receivers in slow moving vehicles but those days are long gone.
As has been stated GPS units average speed over time. D/T = S. The Garmins update about once per second. If it gets one of those 200 or 300 mph errors from a bad position it goes into the pot to be averaged with all the others that are generally within .01% of dead-on. So if you ride any distance at all with updates 3600 times an hour those spurious high (and low - on occasion I have seen my 2730 read low) numbers don't impact the average very much.
GPS is very accurate. It wasn't always so with early single channel multiplexing receivers in slow moving vehicles but those days are long gone.
My top speed is indicating 600MPH at the moment. But I find that my speedo reads higher than my GPS indicated speed.
I just multipy the speed shown on the bike by 7 and thats the mph your over what it is showing..........showing 60... times 7 is 4.2....actual speed is 55.8. At 100 shown you should be doing about 93.
About 7% off. The GPS is more accurate. When the GPS is on the bike I never use the Speedo.
Curt
Curt
i have the tom tom rider and dependent upon speedo reading reads bwn 4 and 8% below the indicated speed. i get back into my bmw car and find the same gps is within 1 % all the time. I can only assume old man H is trying to assist us to preserve some points...
dteel
FWIW I have installed the Speedohealer and have it set at -6.9% and now my GPS and speedometer read identically.
YMMV
YMMV
Oops. In the original post I meant to say that my GPS reads 60 when the speedo reads 65. That is more in line with other's experiences. Thanks.
My comment about lower speed was the same as Ride On . When the States 65 I'm really ding about 58 or 59. I believe Curt has the factor pretty close at 7 % difference.
Joe
Joe
Phartz
Pat Thompson
What you're seeing here is a function of the limited memory for saving tracks that these small units have. The GPS is taking in far more data than is saved in a track. Would not be practical/possible to save it all hence the zig-zag twisties. You'll notice that more points are saved in the twisties than on a long straight. If direction is changing more points are saved. Less otherwise.
A spurious reflection of a satellite signal can cause those bizarre speed numbers. I was coming out of a parking structure among highrises and had a signal bounce me to a point out in the ocean 30 miles away. I had a track leg that had me going 1500 some odd mph for a few seconds.
Delete that one point from the track and you're back to normal. :| GPS speed is very accurate. Moreso than our bike speedos.
I depend on my GPS for accurate speed on my bike and in my cage (Acura - Honda product too.) Both vehicles are about the same off. My friends FJR seems to be much closer to actual and I believe that this is a Honda feature , not necessarily and Japanese MC problem.
, not necessarily and Japanese MC problem.
Yes, as soon as everyone has come to the understanding that I am always right we'll all get along much better.
Actually this has been an issue for me but I don't care if the bike is right since I run GPS. For me I did to have accurate information for rallies so I've done a bit of comparisons to check this. YMMV
Curt
Many posts have pegged the speedo error at 7%. I checked the odometer against mile markers on I-75 for 200mi from the Mackinaw bridge and it was 2.25% over.
BlaSTr
Miami ST
The GPS, if it is tracking enough satellites for a 3D display, will always be more accurate since the error in position is less (I typically get 6-8' when the 276C indicates WAAS and Differential and I'm tracking 8+ satellites). Most GPSs default to displaying data either once per second or Auto. Calculations are done far more frequently than that. On many GPSs you can tell the unit to display speed data more often.
As for inaccuracies in the twisties, since the GPS is recalculating far faster than the normal curve is, it will be more accurate. The display, if set for 1 sec. updates, may indicate a different reading as this is an average of the calculated speeds over that time. Even so, it'll still be more accurate than the speedo. You can set it to continuous, 1sec intervals, or auto. This is why you may see different speeds than the speedo. They're not synched and the default (and only option) on the speedo is continuous.
The next time you ride a challenging road, set the track resolution to something around 10 feet (5.28 would be perfect), run the route, save the track, reset the resolution to something more reasonable and download the track when you get home. The "pips" will indicate the exact position (depending on the resolution of the signal) and you can see how your speed varies in the tight turns. And how many calculations were made.
As for inaccuracies in the twisties, since the GPS is recalculating far faster than the normal curve is, it will be more accurate. The display, if set for 1 sec. updates, may indicate a different reading as this is an average of the calculated speeds over that time. Even so, it'll still be more accurate than the speedo. You can set it to continuous, 1sec intervals, or auto. This is why you may see different speeds than the speedo. They're not synched and the default (and only option) on the speedo is continuous.
The next time you ride a challenging road, set the track resolution to something around 10 feet (5.28 would be perfect), run the route, save the track, reset the resolution to something more reasonable and download the track when you get home. The "pips" will indicate the exact position (depending on the resolution of the signal) and you can see how your speed varies in the tight turns. And how many calculations were made.