I was driving and looking at my GPS speedometer and my cars and noticed that the GPS one is 4-5 mph slower than what the car says, is this common? I haven't changed my wheel size.

 

Yes. My 2009 Justa did this, and I'm unsure if my 2012 does it too.

The dealer told me that in Europe, it's illegal for a car to show a slower speed than it's truly traveling. So to compensate for this, they make the car look like it's going faster than it actually is. So if your speedo says 70mph, you're actually traveling 65mph. This is to help keep the speedo more accurate as you put on a larger factory wheel size, keeping the cars within the European manufacturing law.

No idea if this is actually true, but that's what the dealer said to me when I asked if they could adjust the speedo to be more accurate.

My speedo was 5mph off with 15" wheels. I haven't tested the 2012 yet.

 

Yes this is unfortunately correct. Do a quick search and you will find the many threads showing others' car readouts are off by a few or even more sometimes.

 

Well this is partly true. Yes the laws in Europe state that the speedometer can not show the car going slower than it actually is. And yes there is a software speed adjustment built in. It can be set to off with NCS Expert. Dealers will not and can not do it by law.

As for wheel size. It can change the speed reading of the car. But if wheels and tires are properly done in up sizing the change will be very little.

Also did you know that on a set of 205/45R17 that from brand new to full used (worn to wear bars) there will be a 1.7% difference in your speedometer reading. This is because the tires change circumference as they wear and thus travel more revolutions per mile when fully worn over brand new. BTW the 1.7% equates to a 1.2 MPH change so your speedometer will always be in accurate at some point.

 

I noticed the same speed error on my '02 MCS when comparing it to my GPS.

Because of this, when I replaced my tires I went up one tire size, from 205/45/17 to 215/45/17 (tire dia. increases by .35" and tire width increases by .4")

Now I'm only ~1 mph slow on my spedo.

 

This is normal if you stick with the MINI recommended tire sizes. Common with other cars too.

 

Both my Clubman and my VW indicate about 3 mph faster than actual speed.

 

My 09 JCW is off by +3 mph thats 5% so does this mean my warranty runs out 5% sooner and can this be fixed if not why can't the Germans make a car with a properly calibrated speedo
I check all of my cars over the years and have never found the speedos to be off unless I
went to a larger tire

 

That is what I was thinking initially as well - but it is incorrect.

The speedo is off by ~5%, but the mileage reading on the odometer is correct. The speedo is off on purpose, but not because MINI/BMW don't know how to calibrate it. It is VERY common on relatively modern cars and is something I noticed on the last 3 cars that I have owned.

 

+1 what post #5 said! I did the same tire upsize to 215/45/17 and corrected most of the +3mph error from the factory.

 

I am also considering this (going to 215/45/17) not for the speedo fix but to fill in a bit of the width of my Enkei wheels.

 

What was the setting in NCS Expert for turning this off? It's been a while since I've followed that stuff, last I knew there were some candidates for a correction on/off setting, but none of them seemed to actually have an effect.