My Speedo is off 3mph (fast) in my 05 R53 and using the factory tire size. It’s been that way over a year now and every now and then I check it with gps. I have checked my other vehicles and they’re on the money. So what would cause the issue and how do I correct it?

 

It’s built into the car due to German laws. Big trouble/fines if your your speedo reads too slow so they build in a 3mph margin of safety. The odometer supposedly reads correctly and shouldn’t be inflating the mileage of the car. Not sure if it can be made more accurate using software like NCS Expert or INPA.

 

No kidding?? So all this time I thought the law was letting me slip by.

 

I had the same issue with my 2003 Cooper S. I fixed the error by changing out the stock 195/55-16 tires with 205/55-16 tires and the slight difference in diameter has the speedo reading spot on. No fitment issues with the slightly wider tire.

 

what could I do for a 17” wheel then? My stock size is 205/45/17