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      06-23-2019, 11:27 AM   #1
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Speedo 2 mph slow. How to fix?

2 separate GPS systems record my actual speed (55-85 mph range) as 2 mph slower than: speedo, cruise setting, HUD, and dash computer.

I haven’t tried to compare anything under freeway speed.

Car has original 20” 2H9 package and Dunlop stiff walls, so I don’t think it’s anything to do with tire circumference.

Not a big deal, I just adjust my speed to WAZE or GPS device speed for a long cruise, but I’m guessing there’s a worn part (used to be plastic worm screws in analog cars) that can be replaced or adjusted.

Thanks
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      06-23-2019, 12:48 PM   #2
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Are you new to BMWs? I only ask because this issue (speedo not truly accurate) has been a discussion that I've seen/read about since I've known/owned BMWs (the mid 1980s). I long ago wrote this off as a non-issue...recognizing that my speedo is actually a mile or two below what I'm actually seeing on the instrument cluster. And set my speed accordingly especially if on a long highway trip and using cruise control. Driving around town...I rarely even think about it unless a see the police on ticket patrol...then I know I have a built in "cushion" of a couple of MPH when I glance down to see how fast I'm going.
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      06-23-2019, 01:19 PM   #3
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Speedo error

Quote:
Originally Posted by Qsilver7 View Post
Are you new to BMWs? I only ask because this issue (speedo not truly accurate) has been a discussion that I've seen/read about since I've known/owned BMWs (the mid 1980s). I long ago wrote this off as a non-issue...recognizing that my speedo is actually a mile or two below what I'm actually seeing on the instrument cluster. And set my speed accordingly especially if on a long highway trip and using cruise control. Driving around town...I rarely even think about it unless a see the police on ticket patrol...then I know I have a built in "cushion" of a couple of MPH when I glance down to see how fast I'm going.
Yes, exactly. I remember this from way back to my 2005 330ci and the same is true with my 2016 640 GC. One would think that a company as precise as BMW could make an accurate speedometer. And another thing! How many miles are actually on my car? Is there an algorithm for that? If you think about it, if the speedo runs 2 mph faster the odometer will record more miles than actually driven.
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      06-23-2019, 01:28 PM   #4
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Quote:
Originally Posted by Frupal View Post
One would think that a company as precise as BMW could make an accurate speedometer.

And another thing! How many miles are actually on my car? Is there an algorithm for that? If you think about it, if the speedo runs 2 mph faster the odometer will record more miles than actually driven.
If memory serves me correct...I think the "excuse" given for the speedo is some European Union regulation in regards to the speedometers.

And I believe the difference between the odometer and speedometer is handled electronically as well. We know (based on tech data from the e38/e39/e46/e53 era) that distance data was sent to the ABS unit, then onto the IKE (instrument cluster electronics) by way of the left rear wheel sensor. So somewhere in the mix, the mileage is being recorded...but the speedo is knocking off MPH based on some type of algorithm. So actual mileage is correct although speed/MPH is being slightly reduced as it appears in the speedometer.

EDIT: Here's some old data I had for the e38/e39/e46/e53 generation...see DISTANCE SIGNAL for the correct interpretation of what I was trying to write above. I bet if one searched the TIS for the new generation BMWs...you will probably find similar design parameters/elements:

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Last edited by Qsilver7; 06-23-2019 at 01:34 PM..
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      06-23-2019, 01:55 PM   #5
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there was a secret menu on the 5 that could eleviate this, accomodating the different sizes of factory alloys



correct factor from memory
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      06-23-2019, 02:29 PM   #6
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Quote:
Originally Posted by MARKPRIOR View Post
there was a secret menu on the 5 that could eleviate this, accomodating the different sizes of factory alloys



correct factor from memory
Mark...you make a great point. But I'm not sure it will work (based on past experiences with the hidden cluster TESTs).

The hidden cluster tests are great for accessing operating data/parameters of the instrument cluster electronics...but usually most of the tests only allow you to observe and not manipulate the data/info.

I noticed in the video you linked...TEST 10 would probably be the test for speedo information...but unfortunately the data is "grayed-out" (which usually means you can only observe the data...not change it). If you can change/manipulate the data or access more info...the TEST's text is usually white. So I'm not sure if this is a way to make any changes.

Note all the data for TEST 10 is gray...not white. And I have used the hidden test on my e39 540iT to correct the fuel consumption factor to bring the OBC into proportion with the fuel consumption I was calculating in an Excel file.
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      06-23-2019, 02:36 PM   #7
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I remember “Road & Track” would always note Speedo error on their new car road tests (analog days, when fuel injection was waaay out there).

With everything digital now, you’d think a 2.5% error would be grounds to fire the engineers and sub the work out to HAL 9000.
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      06-23-2019, 02:57 PM   #8
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Quote:
Originally Posted by Roccaas View Post
I remember “Road & Track” would always note Speedo error on their new car road tests (analog days, when fuel injection was waaay out there).

With everything digital now, you’d think a 2.5% error would be grounds to fire the engineers and sub the work out to HAL 9000.
Again, there's a European regulation that requires that that the speedo read faster. Here's some info from this old article: https://www.caranddriver.com/feature...meter-scandal/
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      06-23-2019, 05:44 PM   #9
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Quote:
Originally Posted by Qsilver7 View Post
Again, there's a European regulation that requires that that the speedo read faster. Here's some info from this old article: https://www.caranddriver.com/feature...meter-scandal/
Thanks for clearing that up!
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      06-23-2019, 08:40 PM   #10
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Quote:
Originally Posted by Frupal View Post
Quote:
Originally Posted by Qsilver7 View Post
Again, there's a European regulation that requires that that the speedo read faster. Here's some info from this old article: https://www.caranddriver.com/feature...meter-scandal/
Thanks for clearing that up!
Govt mandated lying. Who'd a thunk ?
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      06-24-2019, 06:44 PM   #11
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I've had this problem on 4/4 bmw's I've owned. Super annoying considering the speedometers on most other cars I've owned have been almost dead accurate +/- 1 mph.
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