I have about 2500 miles on my MCS and I started getting suspicious of the accuracy of the computer, odomoter, and speedometer shortly after I got it. An a recent 1000 mile trip, is checked all three. I checked the odometer against mile markers for 50 miles, timed mile markers to check the speedometer for about 10 miles at a time three different times, and manually calculated the fuel economy for 3 consecutive tanks. The findings

Speedometer: 4.5% fast (reads 71 when you are doing 68)

Odometer: 2.5% low (reads 97.5 miles for each 100 miles)

And the biggy

The fuel economy read high by about 8.5% (shows 30.9 when it was actually 28.5)

The first couple times I checked the fuel economy, I thought maybe I topped it up this time more than last, or the pump was wrong, but I have not checked it every tank and it is consistently wrong by 8-10%. I am happy with the fuel economy, but the computer is way too optimistic. If everything read high, I would blame it on calibration, but the odometer is one way, and the speedometer and fuel economy are the other. Hmm - anyone else have this problem?

 

I've never seen a trip computer in any car that could calculate actual mileage as well as I can with a gas station receipt, my odometer, and a calculator.

 

>>I've never seen a trip computer in any car that could calculate actual mileage as well as I can with a gas station receipt, my odometer, and a calculator.

Ditto.
And if you are getting 28.5mpg in a MCS I'd keep that computer...

 

Our MCS says we are getting about 3MPG better than reality. I have yet to test the Odometer and Speedometer...

_________________

 

A few months back one of the major auto mags had an article on speedometer accuracy. I can't remember which one, but if I find the link, I'll post it here later.

Anyway, the gist of the article was that because of European laws, European cars' speedometers all tend to read high, with BMW being the worst offender. According to their tests, BMW speedos were off by about 6-8mph when travelling at a true 70 mph.

In that test, GM cars had the most accurate speedos. GM beats BMW at something...go figure.

 

>>And the biggy
>>
>>The fuel economy read high by about 8.5% (shows 30.9 when it was actually 28.5)
>>
>>The first couple times I checked the fuel economy, I thought maybe I topped it up this time more than last, or the pump was wrong, but I have not checked it every tank and it is consistently wrong by 8-10%. I am happy with the fuel economy, but the computer is way too optimistic. If everything read high, I would blame it on calibration, but the odometer is one way, and the speedometer and fuel economy are the other. Hmm - anyone else have this problem?

Which mileage were you using to "verify" the fuel economy reading? Your measured mileage or the odometers? This will affect the resulting comparo. Obviously the car is using its own measured mileage which, according to your readings, is less than actual. So, if you calculated using your measured mileage you will show less consumption than the car would - maybe not 8.5% less, but the discrepancy may not be as big as you originally thought. Of course, if you used the odometer mileage for your calculations, then here we are at the point at which we started.

Now, how does tire size affect all of this?

 

Just to clarify a few issues.

The 28.5 mileage I calculated was after adjusting for the inaccurate odometer. The error is even higher if you don't correct for the odometer reading low.

The 28.5 mpg was on a long trip with speeds continuously between 70 and 80. There was virtually no stop and go - gas stops were just off and back on and right back up to speed. That said, I think the mileage is great - I am just bothered that the computer is so inaccurate. Other cars with mileage computers have seemed much closer.

I too recall the article about speedometer accuracy. I think it was Car and Driver. I am not surprised it is off a bit (unfortunately) but I am very surprised that the odometer and speedometer are off in opposite directions! I have had other cars with both off a bit in the same direction.

I have the original run flat 16" tires with 34 psi at all corners.

 

I think mine is off too, I prefer the compute in my Volvo V70/XC. But it got me thinking here, that may be the measurements are imperial, gallons are different, anyone know if a british mile is different than a US mile. A Billion in England has 3 more zeros, right?, I don't remember all this stuff as I've been over here too long.

 

I don't know about my gas mileage, but I pretty much figured everything else was normal....maybe I should pay more attention.

 

I was pulled over by a State Trooper (TX) when my cruise control was locked at 70. The actual speed limit was 60. Whoops! Turns out he just wanted to know what kind of car it was! Wow, I love this car!chandlers4@attbi.com

 

Here is the link to the car and driver article about speedometer inaccuracy

http://www.caranddriver.com/xp/Caran...ds=speedometer

 

The following is from BMW of North America.....it was written to their service personnel.......

QUOTE:

SUBJECT: MAXIMUM PERMISSIBLE SPEEDOMETER ERROR

MODELS: ALL

GENERAL INFORMATION: A certain amount of "speedometer advance" is necessary to compensate for negative tolerances in tire diameter, electronic controls, and other factors. This advance reduces the risk of the speedometer displaying a speed that is less than the vehicle's actual speed.

The amount of speedometer advance can be calculated by inputting a frequency (using the DIS Tester, "Kombi Test Schedule) that corresponds to a given spped and noting the speed that is indicating by the speedometer. The maximum permitted speddometer advance is 10% of the actual (input) spped plus 2.4 mph.

Example:

Acutal Spped=50mph.

50 mph x 10% = 5mph; 5 mph + 2.4 mph = 7.4 mph.

Therfore, the permissible displayed speed is 50 to 57.4 mph.

(Noye: the diaplyed spped must never be less than the actual speed).

No repairs should be attempted if the speedometer advance is within 10% + 2.4mph.

NOTE: The amount of speedometer advance has no effect on recording of actual mileage in the odometer display. The odometer records total mileage digitally and does not incorporate any "advance" tolerances.

END QUOTE.

In regular people talk, this means that if the speedometer on your MINI was originally callibrated for 15" wheels, which it probably was, the speddometer is going to be off when you slap on some 17".

 

Is this why everybody is passing me on the city streets when I think I'm going 10-15 mph over the limit?

But on the freeway, at "70 mph", I'm not in the lower percentile of speed?

 

>>Is this why everybody is passing me on the city streets when I think I'm going 10-15 mph over the limit?
>>
>>But on the freeway, at "70 mph", I'm not in the lower percentile of speed?

If you come to Florida and do 70 on the freeway...
please stay in the right lane....

 

You sure are right about that!
I think the only think that slows people down on I-95 & I-10 in florida is traffic! If there wasn't any they would all have their speedometers pegged.

 

Ok, here's a question I have about this speedometer and computer business:

I set the speed limit chime (NAV system feature I believe) to go off when I hit 75MPH. The speedometer reads about 78 or 79MPH when the chime goes off. Does this mean that the computer is calculating the speed in a different way than the speedo? (It would seem that the computer is more accurate - at least for this bit.)

I have yet to test this at different speeds. ....I just noticed it yesterday.

 

The average speed calculation on my MINI seems to be stuck at 31.5. I just finished a two hour 70 mph trip and it STILL reads 31.5. I wonder if this can be fixed?

 

On our recent trip to St Louis, I looked into the speedo issue. I found the speedo to be off by as much as 5 mph. At an indicated 90mph, the actual speed was 85. At 70 the actual was 67.
I wondered about the indicated vs computer so I set the cruise at 70 on a flat road and reset my "average speed" parameter on the Mini's computer and was rewarded with a 67 mph reading. It will soon begin to average your speed so keep refreshing it for each Mph you want to try. I found the computer to be very close to mile marker calculations.

 

>>On our recent trip to St Louis, I looked into the speedo issue. I found the speedo to be off by as much as 5 mph. At an indicated 90mph, the actual speed was 85. At 70 the actual was 67.
>>I wondered about the indicated vs computer so I set the cruise at 70 on a flat road and reset my "average speed" parameter on the Mini's computer and was rewarded with a 67 mph reading. It will soon begin to average your speed so keep refreshing it for each Mph you want to try. I found the computer to be very close to mile marker calculations.

I did this as well and was rewarded with the correct speed we were motoring. The confirmation occured over the weekend when I was traveling at 70 mph when I came upon one of those radar machines (the ones that give you your speed). I made sure I was at 70, and it clocked me at 66-67.

 

I would say that in the case of the Navagation Unit the GPS is caluclating the speed.

 

>>I did this as well and was rewarded with the correct speed we were motoring. The confirmation occured over the weekend when I was traveling at 70 mph when I came upon one of those radar machines (the ones that give you your speed). I made sure I was at 70, and it clocked me at 66-67.
>>

Hope it wasn't one of the ones with a camera!

 

speedometer's are intended to err on the high side, and BMW has a notorious record for erroring more than any other manufacturer out there! My 325i is a rare example of being only 2% off, but I've seen //M roadsters that are up to 8% off from factory!
It's strange to hear that the MINI's odometer (since it's usually calculated thru the speedo) is reading fewer miles than travelled, but then again, how did this get verified?!