Has anyone else with a Scangauge or other OBDII reader noticed this? I have a PLX DM-200 OBDII reader that reads the data from the car's computer. I also have an Escort 9500i radar detector with GPS that also tells speed by GPS. It has been well documented that the speedo on the R55/56 reads about 2 - 3 mph faster than reality, but the speed on the on the OBDII reader is correct, i.e. it matches the GPS speed which is 2 - 3 mph slower than the speedo. Therefore the internal computer has the right speed, but the speedo, both the analog and the digital one on the tach, is wrong! So it is not a mechanical speed discrepency, but it must be a software "adjustment" going to the speedometer.

Why would Mini do that? Can/would they correct it? Which speed is the car using to determine other data such as mpg, service intervals, miles on the odometer, etc?

Any thoughts on this?

 

Yea, as far as I know they're all like that. I've heard it's to avoid fines by the DOT. If the speed is over it's a sizable fine for import cars. BMW (group) and Audi are about the same over. Not so much at lower speed but up around highway speeds it's about 3mph high. Mercedes-Benz oddly is right on the mark if you compair with a GPS unit. Likewise the odometer, service, etc is sorted out with the "innacurate" speed. It's kinda stupid to me beacuse about 80% of my miles are on the highway!

 

there are at least ten threads on this exact subject. Search is your friend and a requirement of the forums.

Short story - The federal government mandates that speedometers not read slower than the car is actually going and can show up to 10% faster than the car is actually going.

During wear on a standard set of tires the change in the accuracy of the speedometer will change by more than 1.5%. the larger the tire and the deeper the tread on the tire when new will cause larger changes.

Very few cars are actually accurate on the speedometer. All manufacturers must take into account the wear factor on tires and calculate the difference and make sure the speedometer does not read slower than the car is actually going.

Other countries have differing laws about the accuracy of the speedometer but all stat that the car can not be actually going faster thatn the speedometer states. I.E all cars made will read slight high

 

I call BS.........

The speedo on my Audi, my Lexus and my Tundra are spot on, and I've had both the Lexus and the Audi long enough to wear out a set of tires without seeing any appreciable difference in the speedo reading.

As to why MINI do this, I wonder if it has something to do with the CAFE ratings for fuel mileage, 10% is a lot in the CAFE numbers spread over a whole fleet of cars.

All I know is that it pisses me off that the speedo in any MINI I drive is inaccurate this much, I have to take my Garmin with me any time I drive a new one (like a loaner from the dealer) just so I know how fast I'm really going, and I have a 40 mile commute each day, so I need to know. One car the dealer loaned me was off by 7 mph! Unconsionable.

I also don't buy the government mandates the speed read high "just in case" crap, show me where you got that info from the gummint, please .........sounds like urban legend to me. There are too many other cars out there who's speedo reads right on the money for me to buy that.......

 

Honda of America has a class action suit filed against the company 3 years ago, and the court ruled against HONDA.

Apparently this software discrepency was not fixed and went on for years, Tens of thousands of HONDA lease customers hence were overcharged for the "excessive mileage per contract.

If MINI is doing this, it will only be a matter of time before they are sued as well......

 

To be more precise, mine was off by 5%. Changing tires to 215/45s reduced the error to about 3%. So the faster you're motoring, the greater the absolute error.

 

That's exactly right. And that's what Mini "tolerates", up to a 5% delta. Distance is right on the dot (that was my main concern, when I took it to the dealer for this discrepancy - didn't want to get cheated on the warranty).

 

A high reading speedometer is "normal" for many cars. If you do a Google search, you'll find that it is a frequent topic (complaint) in many car forums. These days, speed is digital data and the inaccuracy is deliberately added by the manufacturer, for whatever reason.

Here's a VW service bulletin:

 

This makes no sense. How can VW (or any other car make for that matter) claim to be accurate on distance and not be accurate on speed? ("This factor does not affect odometer readings, which show actual distance traveled." from above).

Different tire sizes would result in differences in distance traveled as well.

 

This is a completely different story. On the Toyota's it was both the speedometer AND the Odometer.

On the Mini the Odometer is correct but the speedometer is off by a slight bit.

You can call BS all you want but the mathematical part of the situation is FACT.

Dulop SP Sport 01 DSST (OEM tire on my MINI)

Here are the specs needed:
Revolutions Per Mile = 853
Tread Depth New = 10/32"
Fully worn tread depth = 3/32"
Mile = 5280 feet or 63360"

So from that we can get the actual circumference and diameter.

Cir = 63360/853 = 74.279015"
Dia = 74.279015/3.141592 = 23.643749"

now we can take the diameter and reduce it by the wear to fully worn

Remember that we are dealing with the diameter not the radius so we have to take twice the wear off or:

10/32 - 3/32 * 2 = 14/32" or 28/64" or .437500"

Now we can reduce the diameter by this number for a worn diameter:
23.643749 - 0.437500 = 23.206249

From that we can calculate the worn circumference:
23.206249 * 3.141592 = 72.904566 inches

This produces a difference in circumference of :
74.279015 - 72.904566 = 1.374449

And we can calculate the change in revolutions per mile:
63360/72.904566 = 869 revs per mile

Fromthat we can calculate the change in %:
853/869 = .98158*100 = 98.1581-100 = -1.8418% change in revolutions per mile.

Thus from this we can calculate that the change in the speedometer will have to vary more than 1.5 % over the life of a tire from new to fully used.

Now the larger the tire and the deeper the tread the more the error will be.

But from this we can also conclude that the mileage on the mileage shown on the odometer will also change during the life of a tire as well. As in when the tires are new (first few hundred miles) for every mile recorded the odometer will record 63,360 inches but at the end of life of the tire the odometer will record 62192.9 inches.

So going on that if you have a car on old tires the car will not travel as far per mile as a car with new tires. thus the warranty will run out early.

Now if you change the tires at say 40,000 miles because they are high mileage tires then you will have a small dent in you warranty (maybe 100-200 miles), but if you change the tires three or more times as they are high performance summer tires then you will have a bigger dent in you warranty (may be 1000 miles)

So math is math and it is exact. I nor anyone else can change that.

Also how does anyone know if the GPS is correct we are just ASSUMING it is correct, maybe the GPS is off.

Now lets look at the OEM tire selections

16" - ContiProContact SSR - 195/55-16 Revs per Mile 844 approx 1.5% different than tires below
16" - Goodyear Excellence - 195/55-16 Revs Per Mile 856
16" - Dulop SP Sport 01 - 195/55-16 Revs Per Mile 856

17" - Dulop SP Sport 01 - 205/45-17 Revs Per Mile 853
17" - ContiProContact SSR - 205/45-17 Revs per Mile 856

18" - Pirelli PZero RFT 205/40-18 Revs Per Mile Unpublished

Now if i changed to a
Yokohama ADVAN Neova AD08 the revs per mile are 859 or almost half way to the minimum limit revs mer mile of the Dunlops. So there is a .85% change right there.

At 60 MPH the 1.8% change is 1.08 miles per hour.