What to believe (ScanGauge & GPS vs. speedometer)

[Green Machine]

My GPS and my SG II agree on my speed. The speedometer shows about 3-4 mph lower than both. I tend to think the GPS and SG are more likely to be correct. What does the group think??

I believe the SG and the speedo are getting the same info from the computer. I think maybe the actual speedo needle isn't very calibrated. The trip odometer is accurate to within 1/10 mile for every 100 miles driven.

Thoughts?

[H4MM3R]

I would go with the GPS and SG.

[cfg83]

H4MM3R -

Originally Posted by H4MM3R

I would go with the GPS and SG.

I agree. Hmmmm. How would you check your GPS accuracy? Maybe walk around a high school running track 4 times and hope it adds up to one mile?!?!?!?

CarloSW2

[Green Machine]

I used mile markers to check my GPS. Get up to a GPS reading of 60 mph and time yourself between markers. If it takes one minute from marker to marker, it's more or less accurate.

[Who]

Funny how the OBDII port tends to know the real speed and distance - meanwhile we lose 4% of our warranties!

[DifferentPointofView]

My GPS shows that I'm 1-1.5 miles per hour off on my speedo. Other people driving behind me tell me that I'm doing 50 when I'm doing 55, but it is THEIR speedo's that are way off. I just can't convince them that, because their cars are newer... pshhh, oh well.

[cfg83]

Who -

Originally Posted by Who

Funny how the OBDII port tends to know the real speed and distance - meanwhile we lose 4% of our warranties!

Yeah, Honda got a black eye for that :

Honda paying out $6 million for 'overclocked' odometers - Feb 19th 2007
http://www.engadget.com/2007/02/19/h...ked-odometers/

... The Society of Automotive Engineers' voluntary standard for fluctuation in an odometer "is plus or minus 4-percent," and strangely enough, the National Highway Traffic Safety Administration doesn't even regulate it. Honda claims that its units were "accurate to within 3.75-percent" on the high side, but a lawsuit against them claims that's just a bit too close for the average consumer's well-being. The automaker will be shelling out over $6 million in overcharges for leasers who were unfairly penalized for exceeding the agreed upon mileage, and will also extend the warranty mileage five-percent. ...

CarloSW2

[DifferentPointofView]

Oh.. that sucks.

Why don't they calibrate speedo's at the factory? I think that's the reason cops don't pull people over anymore unless they're doing ungodly fast speeds because of speedometer error, they could be thinking their doing fine with their speed, but they could have a speedo that's 10mph off like my grandparents RV.

[Who]

DPOV - Speedometers and more importantly odometers never read slow with any factory tire sizes, and the error increases marginally as the tread disappears. In fact by the time you are speeding it should be obvious in many people's speedometers since the indicated speed will be higher than the actual. I can't see cops giving any benefit of the doubt on that.

[DifferentPointofView]

some people's speedo's read low, yet they are going faster than it says.

Well, I guess it's just my tires, cause they're almost to the replacing point!