Odometer reading verses GPS?

[PHeadings]

Odometer reading versus GPS?

Did a 500 mile trip this past weekend and it appears my stock speedo is off. Reset odometer and Magellan 700 (GPS) before leaving and returned with 500 miles on the odometer and 480 miles on the GPS. That puts the speedo at 1 to 2 miles per hour faster than true.

With the cruse control set I noticed the GPS would give a speed of 68 MPH while the speedo said 70 MPH. Also noticed radar signs on the side of the road would coincide with the GPS.

I'm running the stock tires that came with the truck, guess the speedo will be right on when I get the new 285's tires.



Has anyone else checked there speedo?

 

[klenger]

Mine is within 0. 5% if I remember correctly. I would not trust the GPS to keep accurate track of milage over long distances, especially if any of it is city driving. GPS distance traveled is a calculated field and can be off some in driving with a lot of turns. It should be pretty close on a straight and level section of freeway though. The dealer should be able to recalibrate your spedo.

 

[RustyJC]

Dunno about mileage, but speed on my Garmin 2620 is within 0. 5 MPH (as close as I can read it) of the stock speedometer.



Rusty

 

[XJSuperman]

the MPH on my GPS is nearly 100% accurate. BUT as was stated above... I would not use it to calculate long distance mileage as you have to figure... most GPS are accurate to what... 10 feet or so. That's a good bit of difference over a long distance. PLUS if the GPS ever gets lost (loses signal) and you didn;t see it do so... you lose mileage on it there as well.

 

[Hercules130]

i know some vehicles have there speedo's calibrated 1-3 mph faster, so you actually are goin slower than you think. my cousins wrangler is off about that much

 

[PHeadings]

I find it very funny that they do this. If I guy is a few houndred miles past his warranty the question would be is it really out of warranty if the speedo is set from the factory 1 to 3 mph faster than true.

 

[Dean Upson]

Speedometer and SP-III are on the money.



Dean

 

[MABurns]

Did a 500 mile trip this past weekend and it appears my stock speedo is off. Reset odometer and Magellan 700 (GPS) before leaving and returned with 500 miles on the odometer and 480 miles on the GPS.

Has anyone else checked there speedo?

I agree with all that say there is more margin of error in the GPS for measuring distance but if it is accurate and your speedometer is off..... @ that rate you have a 34,560 bumper to bumper warranty and a 96,000 mile engine warranty!

 

[DBond]

The speedo system is going to have a little variation from one unit to the next. Tire presure and tread depth will make a little variation. I think the manufacturers typically set the speedo so that the higher reading units will be right on, so if someone is speeding it's not the manufacturer / equipment. That would leave the typical unit reading a bit high.



I think the GPS can be very accurate, but it depends on the circumstances. If the signal was weak or lost at times (tall buildings, tunnels, mountains) it could be way off. A trip with lots of turns and curves probably has more accumulated error than a straight line.

 

[WStoops]

Checked mine several times against a measured mile and it was as close to right on as I could determine.

 

[PHeadings]

Yes, Four satellites North, South, East, West of you have to lock on your ESN before moving the GPS for proper tracking, but the thing I guess I'm not understanding is why Dodge would Sell new trucks with the speedo being off 1 to 3 MPH?
I know my GPS is on because it uses the same technology (satellites) are government uses to guide a 10,000 lb warhead to it's destination.
Also while driving into construction zones the radar posted speed sign shows consistent with the GPS 2 MPH off.
Now don't get me wrong I think it's ok set like that might save me a ticket or two, but what about warranty issues. True mileage?

Hey, How many miles do you have on that thing?

90, 100 thousand you know!

 

[scootergmc]

I had the same question a while ago, and mine is right on. Can't complain.