Accuracy Of Odometer

[Montyone]

I have now done 7500 miles in my Verso T180 and today did a round trip of 400 miles on business. I use a Garmin Nuvi 865T sat nav and noticed a discrepancy between the mileage on the trip meter on the nuvi compared to the car.

Having reset the trip meter on both, the car stated that I had done 396 miles while the satnav stated 402 miles.

Has anyone else noticed this? It may not be a big difference but if you do enough miles, it will add up.

[yoast]

I would bet on the Satnav as being the most accurate any second.

Your odometer is one of the better ones, but will not match the accuracy of a GPS (Unless your GPS is defective, of course).

cheers.

I have now done 7500 miles in my Verso T180 and today did a round trip of 400 miles on business. I use a Garmin Nuvi 865T sat nav and noticed a discrepancy between the mileage on the trip meter on the nuvi compared to the car.

Having reset the trip meter on both, the car stated that I had done 396 miles while the satnav stated 402 miles.

Has anyone else noticed this? It may not be a big difference but if you do enough miles, it will add up.

[hertsnminds]

I used to own a Garmin eMap and because it was not very good at keeping a GPS signal it would loose tracking every so often and always read fewer miles than my cars odometer. I now have a Garmin Nuvi 610 which can take up to 1 minute to get a satellite lock from start up. I would suggest the GPS is less accurate as it has to guess how far you have travelled between any loss in GPS signal.

The only thing that might make the cars odometer less accurate would be a non standard wheel/tyre size.

[yoast]

Tire size is not the only factor.

http://www.newsnet5.com/money/14535385/detail.html mentions investigation in the US & it lists factors affecting accuracy:

- Tire pressures - affect the effective tire circumference and therefore the mileage.

- Tire wear - same reason as for 1.

- Tire make / model - coefficient of friction (or grip) changes and this could affect the displayed mileage in certain situations if the slip changes significantly.

- Road surface - dry v. wet or sandy surfaces could affect slip and thereby affect odometer mileage.

- Ambient /road surface temperature - tire pressure changes and affects tire circumference, etc.

- Vehicle loading - same reason as in 5.

- Different wheel / tire sizes offered on a model - same reason as for 1.

- Tolerance stacking and wear of components involved in odometer mileage computation.

btw. I do not think the test of driving 1 mile in this article is accurate enough. Test on at least a 100 miles of fairly straight freeway. Test by taking a 100 mile distance as accurately as possible and marking the 2 points as accurately as possible (as waypoints). Drive and then compare odometer and GPS performance.

GPS's will have factors affecting their accuracy as well.

Starting and ending positions should be very accurate. In between it becomes less clear.

http://ttraz.wordpress.com/gps-measuring-a...how-much-trust/

In cars, however, the travelling is much more in straight lines. Particularly on the type of travelling where it becomes interesting to know exactly how far you've driven.

I would easily bet on them being more accurate than an odometer on a trip on the order of 400 miles a day. A GPS that logs its trackpoints could be used to plot the actual track and estimate the distance travelled in Google earth or Ozi-explorer. I just rely on it to be accurate on average.

As technology progresses these algorithms may be improved as well.

cheers

I used to own a Garmin eMap and because it was not very good at keeping a GPS signal it would loose tracking every so often and always read fewer miles than my cars odometer. I now have a Garmin Nuvi 610 which can take up to 1 minute to get a satellite lock from start up. I would suggest the GPS is less accurate as it has to guess how far you have travelled between any loss in GPS signal.

The only thing that might make the cars odometer less accurate would be a non standard wheel/tyre size.

[Mikeangelo]

Hello from me also,

On my verso, with factory default tires, recommended tire pressure, the measured speed by the odo and by GPS is about 10%. The car shows 155, the GPS reads 139. The systematic mistake is present throughout all speed. I read and hear such mistakes are usually embedded by car manufacturers in order to show better fuel economy (e.g. actual 91 km instead of 100) and in order to give the driver a safety tolerance and comfort zone.

BR

Michail

[Haylands]

Hi

Speedo's are not allowed to under read, i.e. it cannot say you are going slower than you actually are, they are allowed to be 10% inaccurate. This is a construction and use regulation.

Therefore as the trip and mileometer use the same system as the speedo needle to record, they will also read under, mine is nearly 10% out....

My fully fitted Kenwood satnav gets a lock in less than 100yds and I have yet to see it loose a signal whilst going... the speed difference between the speedo and satnav is

Indicated 70mph on speedo 64mph on sat nav....

The trip on the satnav is always showing less miles with mine...

The closer the manufacturer gets to the 10% error the better the mpg will appear...... after an hour the car thinks its done 70miles when in fact it's only done 64....

I can't understand how yours can show more miles.... how does the speed compare?

Pete

[yoast]

Hi,

I have just done some 2000 miles of holiday driving and I can say that my Garmin consistently reports speed as about 10% lower than what the odo reports. If I pick 110 km/hr the GPS will say 99km/hr. If I go for the 130 km/h speed limit on the French motorways the GPS will say 117km/h On long stretches of motorway I have compared them repeatedly for miles travelled, speed etc.. The GPS was very accurate judging by the wee mileage poles beside the motorway) the odometer was quite a bit off.

Odometers do not just have some inherent unreliability (like any tool), they are set up in a way that does not make them very accurate. Whether this is due to poor calibration, safety margins for manufactureres or deliberate overreporting is not clear to me.

Hi

Speedo's are not allowed to under read, i.e. it cannot say you are going slower than you actually are, they are allowed to be 10% inaccurate. This is a construction and use regulation.

Therefore as the trip and mileometer use the same system as the speedo needle to record, they will also read under, mine is nearly 10% out....

My fully fitted Kenwood satnav gets a lock in less than 100yds and I have yet to see it loose a signal whilst going... the speed difference between the speedo and satnav is

Indicated 70mph on speedo 64mph on sat nav....

The trip on the satnav is always showing less miles with mine...

The closer the manufacturer gets to the 10% error the better the mpg will appear...... after an hour the car thinks its done 70miles when in fact it's only done 64....

I can't understand how yours can show more miles.... how does the speed compare?

Pete