Have around 2K miles on my MCS. On a recent trip I was trying to guage the accuracy of the speedo. I reset the average speed on the computer. After a few miles of cruising steadly at an indicated 77-78 mph (approx) the computer said 71.6. Anyone else suspect there spedometer is off?

 

First, the MINIs speedo reads about 3 to 3.5 mph slow. I have a GPS unit, and say you tell it to calcaluate your speed when the speedo says 70, it really is about 66.5 to 67 mph. Unfortunaly, its lead me to travel at faster speeds (falsely) thinking I'm going slower.

The crusie control is a POS in my mind. The last car I had, once you set the crusie control, you remained at that exact speed, and you never saw the speedo move positions, even with mixed hills. I'll see the speedo increasing in speed past what I set, and then I reconfimed with the GPS that I really was going faster. I've calculated that it varies both up and as much as 4 to 4.5 mph (unacceptable in my mind). Anyone know, are other new model BMWs like this?

Anyway, hope that helps,
Erik

 

I too used my Garmin GPs to determine mph vs the speedo. Any difference could be influence by the +- 7 meter error of the Garmin Legend. So I used this table to determine my true mph over a "measured" mile. A simple yet elegant solution to verify true mph:

Seconds Road
Per Mile Speed, mph

50 72

51 71

52 69

53 68

54 67

55 65

56 64

57 63

58 62

59 61

60 60

Give it a go.
SMKKVK

 

I've noticed the same thing although mine isn't nearly that bad. The average speed on my computer is about two or three mph slower than what the speedo says. I'm talking about if you reset it while crusing at a steady speed on the interstate or something. I'm curious if the speedo error (in relation to what the computer says) is the same percentage as what the computer reads for mpg (in relation to what you get doing it the old fashioned way).

 

It's been posted on MCO before (perhaps by you, SMKKVK?) that the speedometer gets more inaccurate (on the high side) as you increase your speed on the MINI. Something in the neighborhood of 2-3 mph at 40 mph, up to 5-7 mph when you get over 100 mph.

 

An analog speedometer that is not perfectly calibrated (and our's are NOT) will always be off by a certain percentage. If it is 5% off, that is only 2 mph at 40mph. But at a high speed, such as 120, you speedo could get close to reading 10mph faster or slower than you are actually going.

I have found that my speedometer is off by about 4mph at 75mph. It says I am going faster than I really am according to my Garmin Streetpilot III GPS.

When my GPS recorded 120mph, the speedo was approaching 130 when i very briefly glanced over to compare.

 

On my 03 MCS I found that the analog center speedo indicates a higher speed than actual by about 3 mph at 75 mph, and the OBC average function indicates a lower speed than actual by about 2 mph at the same speed. The two thus differ by 5 mph at 75. This is after receiving a new speedo cluster to replace a defective temp gauge. The old analog speedo over-estimated by 4 mph at 75.

 

OK, I took my center console apart to see what's going on.
Several things:

I had to deal with screws filled with solder:
and house-numbered ICs, but I think I understand a lot more.
And I didn't break anything!!!

You can see for yourself here MINI Speedometer cluster

The moral of the story is that I think we're stuck with the innacurate speedometer for a while until I look into
the CAN protocol some more as I try and replace my Tachometer cluster with something a bit more sleak.
Tachometer thread.

 

In EU the governments mandates that the speedo have a degree of error built in. It will always overstate the speed you are going and the error will get bigger the faster you go (from memory). So the speedo is not broken it is just doing what it is told.

Another interesting fact about the speedo is the speed is measured and calculated in KM/h and then displays it is other formats. eg MPH

Trippy do you have any more photos of the inside of the speedo?

 

>>Another interesting fact about the speedo is the speed is measured and calculated in KM/h
>> and then displays it is other formats. eg MPH

Does it matter what units are used internally?

KMH^-1 or MH^-1 or Feet-Second^-1 for that matter. It's just a
speed, and then someone does the speed-to-angle conversion depending on
the scale on the speedometer, and BANGO, you've got the pointer pointing at
the correct number. Nww if you had limited precision, you could have a
bit of a problem, but people understand how to do this conversino, so you are not
going to get (much) error from conversion.

(And the speed is really measured as wheel-revolutions-per-second, not KMH^-1
anyway. Or maybe some internal gear in the tail-end of the transmission)

>>Trippy do you have any more photos of the inside of the speedo?

I do, and I'll post them after August 19 ehdn I return from Cape Cod, MA

And one last thing: Could you look up that EU rule that says speedometers have to be
wrong? I think it's on old-wives-tale that car-people tell each other, and I'd like
to see some evidence that it is indeed a law somewhere.

 

Here you go. Don't know if the EU reg are online for free but you could have a look to see the size of the error.

"An interesting article in the the April 2002 issue of Car and Driver concerning speedometer accuracy explains why European cars have speedos that read slightly high.

The article asks the question why European cars typically have speedometers that do not reflect actual vehicle speed as accurately as speedometers in cars from North America or Asia manufacturers (based upon years of Car and Driver test data).

The article specifically mentioned BMW and Porsche speedometers (which does seems to include the MINI). Of course having a European car with a less accurate speedometer is very much counter-intuitive when you consider the high speed autobahn travel possible in parts of Europe.

The upshot: A certain level of inaccuracy is designed in on purpose by the manufacturer in order to meet EU regulation ECE-R39. Mostly this has to do with making sure the speedometer never underreads true speed. This is important, the EU feels, because a car owner may fit a variety of different -- usually larger -- wheel and tire combinations to a car.

This also has a side benefit for the litigation-happy US market: it helps prevent lawsuits of car companies by disgruntled drivers who get speeding violations. By ensuring the speed that appears on the speedometer is higher than actual speed they can't complain they didn't know they were speeding!

Here's the real interesting tidbit: Trip Computers do not have to meet the EU ECE-R39 regulation, so they tend to read more accurately. Meaning if your speedometer says you are going 80 mph and you maintain that speed and reset your trip computer to determine your real average speed, the Trip Computer will show the more accurate, (i.e. slightly lower), true vehicle speed. I know that on my own Cooper S, 70 mph on the speedometer reads as 67.8 mph on the computer."

 

Had quick look, and here is the full reg Click here

 

>>I too used my Garmin GPs to determine mph vs the speedo. Any difference could be influence by the +- 7 meter error of the Garmin Legend. So I used this table to determine my true mph over a "measured" mile. A simple yet elegant solution to verify true mph:
>>SMKKVK

Hi everyone,
Even though GPS units may state that it has a +/- 7m error, when measuring speed GPS is a lot more accurate than that. The reason is that even though it may be 3 meters off in this reading, it will probably be 3 meters off for the next 10 or 20 readings as well. This is why WAAS and LAAS works; GPS position error in your general vicinity is very consistent.

I would not be surprised if the difference in position error from one reading to the next is only fractions of an inch.

Also, when traveling at speed, even a 7 meter error is only 0.7% per kilometer. A one second difference in measuring your mile will lead to an error greater than 1%. Therefore, using your GPS is still the most accurate way of getting your true speed.

Hope this helps.

 

Thanks for putting it more understandable about the GPS in words better than my own KatanaPilot. I just love my Garmin Streetpilot III and it is great to know that it is highly accurate compared to my speedo which seems to show speeds about 4-5% faster than actual.

 

Snoopy, thanks for the very interesting information about the EU regs! I'd never heard it before, but then again this is my first non-Japanese car.