Don't know if anyone have the same problem but I think my spedometer is off on my 530i by approx. +3~4 mph. I drive by one of those speed radars that they put on the side of the street on the way to work everyday, and it's always reading 3 to 4 mph slower than what is on my spedometer. At first I thought the radar was off but I drove by another one today at a different location and it clocked at the same speed.
Could this have been done intentionally by BMW?

 

Yes this is done intentionally, I think there is some law about making the speedo over read in all cars. Every car I have ever driven over reads.

I have checked this with my GPS. Indicated speed 130km/h actual speed about 125km/h.


My Landrover Horror Story

 

The actual speed is either 5km or 5% slower (can't remember which). Can check your real speed yourself without all the gadgets. Search for the thread on reading your speedometer accurately by the above author (I think).

 

I regularly check my speedo reading against my GPS Snooper. When new, the reading was as near 100% accurate as you could get. I have now done 10,000 miles and the readings are approximately 2% high. Now, I am fairly sure that the electronics won't "drift" so I tried to work out the physics. I can make up some of the difference by the tyre wear which will effectively reduce the circumference of the wheel and I can only put the rest down to an increase in flexibility of the tyres as they have worn in. Again, slightly lower profile leads to reduced diameter etc.(I check the pressure, so it is not down to that.) I can't find a way to calculate this, but I can't think of another variable which might account for it.

At least the small inaccuracy is on the high side which is safer!

 

Well as the tire gets smaller it spins more times per mile. Not manny but a few. This could be the cause of your problem. Also, most BMW's are 2-3 mph slower than they say they are.

 

In europe especially the car manufacturers are suseptible to VERY HIGH fines if the KM/H / MPH reading is showing slower than actual speed. You will always notice Audi, BMW, Mercedes & Volkwagen being off the most - generally between 3-5mph.