Speedometer Readings?

[sdrege]

Maybe you folks can help a realtively new BMW owner...
I have a 2000 Z3/2.3, and (after my wife drove the Z3) a 2003 525i.

I recently acquired a hand held GPS and found that the speedometer on both cars overstates the speed. Somewhere in between 5-10 percent.

On my Z3, I initially thought that perhaps the previous owner had changed wheels, etc., and I was comfortable living with the discrepancy.

My wife's car - a totally stock "Certified Pre Owned" car bought from a BMW dealer - has a speedometer that does the same thing.

I would think that the GPS Navigation systems are accurate because they calculate the speed based upon the movement.

Has anyone seen or heard of anything like this? Any thoughts?

[CassiesMan]

My money says that your GPS is off. Those handheld units are meant for finding your way while walking through the forest, and most humans aren't gonna be moving faster than 10 mph, and even then, there are few that can do that. Its most likely a lag between the GPS unit and the satalite trying to keep up.

[sdrege]

Originally Posted by sdrege

Maybe you folks can help a realtively new BMW owner...
I have a 2000 Z3/2.3, and (after my wife drove the Z3) a 2003 525i.

I recently acquired a hand held GPS and found that the speedometer on both cars overstates the speed. Somewhere in between 5-10 percent.

On my Z3, I initially thought that perhaps the previous owner had changed wheels, etc., and I was comfortable living with the discrepancy.

My wife's car - a totally stock "Certified Pre Owned" car bought from a BMW dealer - has a speedometer that does the same thing.

I would think that the GPS Navigation systems are accurate because they calculate the speed based upon the movement.

Has anyone seen or heard of anything like this? Any thoughts?

Oops, I guess I should'a searched the web before posting.....

This is a copy and paste from another site (Sorry if there is a copyright violation here?)

[Start Quote]

The reason BMW speedo's read high (as well as Mercedes and Porsche) is that there are TUV laws in Germany that require the speedometer to NEVER read low, for safety. All three companies calibrate them slightly high for this reason.
When the cars are inspected over there, the speedometer MUST read what the actual speed is or higher, if it reads below what the actual speed is by any amount, it's large fine time.

Correct, this is not only in Germany but most countries.

In Germany the law states the speedo must be between 0% - 7% of the actual speed. BMW set the tolerance in the modern cars at 5%.

Millage reading is not affected.


[End Quote]

I also found another site that indicates how to correct this. Its at:
http://www.ibmwr.org/otech/speedo.html

Sorry for the false alarm. But maybe there's some useful info here in this thread, after all...?