How accurate is your speedometer
 

After noticing a lot of cars tailgating me, I thought I would check my speed with a GPS. I found the speed to be out minus 10 kilometers/6.2 mph when traveling at 60k/37mph. Do you think this is excessive and Is there any way to have this adjusted?

You can have your speedo calibrated. That seems pretty excessive, I wouldn't expect to see more than a +/- 2 mph difference.

Speedometer error
 

Do you have stock tires?

Wayne

I've got the standard 18's. It's a bit of pain having to calculate your actual speed to compensate for the error all the time.

I would take it to a dealer and say that its a brand new car w/ stock wheels and tires and have them fix it. That is very excessive in my opinion

Do u really think a signal from a satellite is going to give u a better reading than ur car? Go to the track n use a laser. That should be a lot more accurate.

Yeah they are spot on! I've got two GPS units that both measure my speed identically. They are also spot on when approaching one of the "Your speed is" signs. ;-)

Its usually a percentage, not an actual number that is off.

On my mini it was roughly 9% off.

the Z is a little better, at 7.7% .

I checked mine with my GPS and it is off about 1 MPH.

^ at what speed?

70 - 85 MPH (or 71-86 MPH, however you look at it :p)

My Z is right on, perhaps just a small fraction off at highway speeds. No more than 1 MPH at 60 though.

Again, you need to study up....:shakes head:

"Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on."

trust the gps

According to all the local radar stations, my speedo is dead on.