Odometer Error

I just completed a trip during which I kept track of my total mileage on both the Trip 2 odometer and with the Trip A on my Nav V.

Trip 2 = 1121 miles

Nav Trip A = 1151.1 miles.

Any ideas why the two do not agree? Both were reset at the same time at the beginning of the trip.

That's a 2.6% error that's most likely due to speedometer error. Wear on the tires even could cause that (as they wear their diameter decreases causing actual speed vs. indicated to decrease). GPS would rule here as it isn't affected by any outside factors. My Camhead's speedometer reads about 2.8% fast (72 indicated vs 70 actual per GPS).

I just completed a trip during which I kept track of my total mileage on both the Trip 2 odometer and with the Trip A on my Nav V.

Trip 2 = 1121 miles

Nav Trip A = 1151.1 miles.

Any ideas why the two do not agree? Both were reset at the same time at the beginning of the trip.

Afternoon KSB

As mentioned probably some odometer error but some of the error is due to the way a speedometer/odometer reads & how a GPS reads. The road surface odometer reads actual tire travel distance & the GPS reads travel distance against a distant set of satellites. The GPS doesn't track exactly around curves or up & down hills as it kind of truncates the data points.

Also, a motorcycle tire isn't flat (it has a curved tread profile) so every time the bike is leaned over in a curve or turn the wheel speeds up slightly for the same distance traveled.

If you ran a straight line (no curves or hills) then the GPS & the odometer should read pretty close (assuming the odometer is accurate).

There might also be some intentional under reading programmed into the bike's odometer after the past deal with Honda (cars) reading on the high side therefore ending the warranty coverage early (some law suits on this one).

The GPS doesn't track exactly around curves or up & down hills as it kind of truncates the data points.

This is true though these days GPS units recalculate so often (at least a couple of times per second) that this effect is pretty small. Regardless, when I did the comparison on my RT I ran down a stretch of highway that almost arrow-straight for 3-4 miles.

That's nothing. I have experienced >250,000 miles error in GPS reported mileage, as well as top speed above Mach 2.

Thanks for all the inputs.

I assumed (yes, I know) that the Nav V got it reading from the same source as the Trip odometers did, like the extra screen data for the GS bikes.

"The GPS doesn't track exactly around curves or up & down hills as it kind of truncates the data points." My speedometer and GPS always track within 1 mph. Also, the Nav V Trip A reads higher than the odometer Trip 2. Won't the Nav read lower if it truncated the points through a curve?

I'll try running down a lengthy stretch of straight highway and see if I get an error there (should be easy here in Florida).

Does your NAV 5 speed indication match your bike speedometer? My 2015 RT speedometer reads slightly higher at 60 mph.

Here is something interesting I just found

“Not my recreational GPS. Its ground track often shows zig-zag patterns across the road. When traveling through some river valley with poor reception while the overhead satellite constellation is sparse, the deviations off the road can be huge.

The resulting zig-zag path is usually longer than the paved path of the car.”

My speedometer matches the Nav V within 1 mph at all speeds. I can see that the Nav V track would be longer if the track zig zagged across a road; interesting phenomena.

Thanks for the input.

My speed on the RT digital display is always +2 mph over what my Nav5 reads. Down at 10 mph all the way up to 100mph. I've honestly never checked the mileage difference over a long trip. TBH, I don't really care all that much. It's good enough for government work. :-)

Mine is +2 up to 70 and then +3 at 80. I don't really care about +- a few mph at felony speeds.

I have a NAV VI installed on my 2015 RT. In my experience , every motorcycle I have owned has had a Garmin GPS unit installed on it. On my all my bikes with GPS I always set cruise to the speed that is displayed on the GPS and ignored the speed displayed on the speedometer . I have never gotten a speeding ticket. I have found that MOST bikes display on the spedo about 2-3/12 MPH higher that actual speed according to the GPS . My KLR 650 was the worst ( 5mph over ) and my RT was in-line with most other bikes I have owned / own.( Yamaha , Harley, Harley, Harley LOL and Honda) ) I regularly cruise past the police at 66 mph on 55 MPH zones and at 72 in 65 MPH zones and have not gotten a ticket ever. My friends always slow down when an officer is present and I just keep on going at my speed never to receive a ticket. I do remember reading an article in Ryder Mag about how most moto spedos are off by 2-3 MPH. in favor of the slower speed

Having spent many years riding motorcycles with calibrated speedometers in addition to a GPS device, I can confirm that apart from a bit of lag during acceleration/deceleration, GPS devices are perfectly accurate.

I have owned three BMWs. All have read greater than the gps. At 70 it is 2-3mph difference. I find when I follow cars they will consistently be doing 53 mph indicated on the gps. They may think they are going 55. Drives me nuits lol. I haven't routinely checked the miles on the bike odometer vs the gps. I did notice doing a SS 1000 that there was a difference between the bike and the gps. I can't remember the discrepancy. I think the gps showed more mile than the bike.

European regulations require speedometer testing at 40, 80 and 120 kph. Accuracy requirements for motorcycles are a) the speedometer must never read less than the actual speed and b) the maximum amount the speedometer can read above the actual speed is 10% of the test speed plus 8 kph. So at a test speed of 80 kph the speedometer could read as much as 92 kph and still comply with the regulation.

European regulations require speedometer testing at 40, 80 and 120 kph. Accuracy requirements for motorcycles are a) the speedometer must never read less than the actual speed and b) the maximum amount the speedometer can read above the actual speed is 10% of the test speed plus 8 kph. So at a test speed of 80 kph the speedometer could read as much as 92 kph and still comply with the regulation.

Your math is different than mine.

A test speed of (80 kph + 10-percent = 88 kph) + (8 kph) = 96 kph. But you knew that.

What I find more interesting is that a test speed of 80 kph and an indicated speed of 96 kph yields an error of 20.0-percent, which is huge.

Tim

European regulations require speedometer testing at 40, 80 and 120 kph. Accuracy requirements for motorcycles are a) the speedometer must never read less than the actual speed and b) the maximum amount the speedometer can read above the actual speed is 10% of the test speed plus 8 kph. So at a test speed of 80 kph the speedometer could read as much as 92 kph and still comply with the regulation.

My BMW cars have always read high too. The regulations favor the engineers to intentionally set the speeds to be slightly higher than actual since they can get fined if they read less than actual.

European regulations require speedometer testing at 40, 80 and 120 kph. Accuracy requirements for motorcycles are a) the speedometer must never read less than the actual speed and b) the maximum amount the speedometer can read above the actual speed is 10% of the test speed plus 8 kph. So at a test speed of 80 kph the speedometer could read as much as 92 kph and still comply with the regulation.

 

Your math is different than mine.

 

A test speed of (80 kph + 10-percent = 88 kph) + (8 kph) = 96 kph. But you knew that.

 

What I find more interesting is that a test speed of 80 kph and an indicated speed of 96 kph yields an error of 20.0-percent, which is huge.

 

Tim

Tim, you are absolutely right...

.... and the error would be 26% at the the common urban speed limit of 50 kph.

What do you think would happen to sales if a manufacturer ever released a motorcycle with that sort of error? A fellow trying to observe the speed limit would be overtaken by all his buddies on bikes with accurate speedometers.