Speedometer recalibration?

[alohart]

With so much behavior governed by parameters that various electronic controllers read, BimmerCode might be able change the value of some parameter that affects the calibration of the speedometer. However, we'd need someone fluid in German who could interpret the names of hundreds of parameters to identify parameters to try.

 

[Dutchi3]

The speedometer of my van from '86 is entirely mechanical, with a bowden cable connected to an analog meter. It is spot on with gps measurement, so 50 miles actual speed is 50 miles in the display. Things have changed indeed.

 

[Tecam]

My 2019 i3 120 reads 2mph slow at 30mph - (i.e. 28mph) according to the radar displays on speed limit signs……

 

[JTylee]

All BMW's have a 2 mph discrepancy, since the days of the E30, it IS indeed a German Law.

I've owned over 14 BMWs and it held true every single time. Fun fact: I put the style 431 S wheels on my regular i3 and now I'm only off by 1 mph

But yes, it's not a wives tale, it's not an urban legend, it's an actual thing.... ALL BMWs do it...

 

[Tecam]

I have a Garmin that I rely on for speed and other traffic and road data, since the speedo in my i3 typically reads about 3mph low at highway speeds, and the i3's nav is sadly out of date. Let's hear it for free lifetime map updates!

Hooray! Same as mine, reads ~2 to 3 mph LOW - despite the claim above that “they all read high”

 

[alohart]

Hooray! Same as mine, reads ~2 to 3 mph LOW - despite the claim above that “they all read high”

Are you running OEM tires or at least tires of the OEM size?

 

[Tecam]

Are you running OEM tires or at least tires of the OEM size?

OEM & replacements of the same size give same results. I may have misread (or misunderstood) the above claim, I was wrongly thinking it was meant the cars’ speedos were actually exceeding the actual (real) speed…….

 

[mojo]

Although there are a few exceptions, the main purpose of the speedometer is to prevent you from inadvertently exceeding the speed limit. So any speedo that under-reads your actual speed is not serving that purpose correctly. Hence the regulations on speedo accuracy allow for it to over-read by up to a certain amount, but do not allow it to under-read.

In Europe (inc. the UK) the accuracy for vehicle speedometers is defined in EU Regulation 39 (I believe current reference is E/ECE/324/Rev.1/Add.38/Rev.2/), and this has been the case (with minor amendments) since 1975. This states the following:

The speed indicated shall not be less than the true speed of the vehicle. At the
test speeds specified in paragraph 5.3.5. above, there shall be the following
relationship between the speed displayed (V1) and the true speed (V2).
0 < (V1 - V2) < 0.1 V2 + 4 km/h

[Note that the "<" symbol should actually be the "or equal" version but I can't find a way to make that display correctly]

As far as I'm aware, there is no "German law" that overrides this - it applies equally in all EU countries, though it has been adapted in the UK to allow for the fact that MPH is used there rather than km/h.

 

[Nanniepoo]

Less than or equal can be typed out as <=

 

[mojo]

I've no doubt there's a Unicode character that I could have inserted, but in this situation it's an edge case that isn't likely to be important, so I couldn't be bothered to use the Character Map tool to find it.

I should add that the main reason for such a broad "permitted" band is not so much about quality of calibration, but more to do with the fact that analogue speedos are not very linear (because of the way in which they work). In that respect, the existing regulations are archaic, because those limitations don't apply to digital instruments.

 

[ksnax]

It's all arbitrary ultimately. We would not need them at all or speed limits if people just drove prudently for the road and conditions. Here in Oregon, and likely many other places, we do still have what is called the 'Basic Rule', which essentially means the limit does not matter if you drive like an idiot. I just keep pace 99% of the time now.

 

[eNate]

We would not need them at all or speed limits if people just drove prudently for the road and conditions.

Perhaps, but "prudent" to you may mean something different to my mother-in-law or my teenage son, and most certainly would mean something different to an speed -trap officer in Peninsula, Ohio versus an overworked beat cop here in Oakland.

 

[alohart]

Less than or equal can be typed out as <=

Or ≤ (Option-< on a Mac with a U.S. keyboard)

 

[alohart]

I may have misread (or misunderstood) the above claim, I was wrongly thinking it was meant the cars’ speedos were actually exceeding the actual (real) speed…….

You were thinking correctly. The speed displayed by most cars' speedos exceeds the actual (real) speed.

 

[ksnax]

Perhaps, but "prudent" to you may mean something different to my mother-in-law or my teenage son, and most certainly would mean something different to an speed -trap officer in Peninsula, Ohio versus an overworked beat cop here in Oakland.

LOL. True, but 'prudent' is often decided by judges and juries to have more pragmatic limits.

 

[Whereitis]

Hooray! Same as mine, reads ~2 to 3 mph LOW - despite the claim above that “they all read high”

I misspoke. My i3 speedo reads high not low. On cruise at 81 indicated on my i3 speedo, my Garmin reads 78mph. At lower speeds it still reads high but not as much. At 40mph on the Garmin, the i3 says 42. At 20, the i3 says 21. It's like they want you to think you're going faster than you really are. But now I question the odometer, which is a critical tool in a car with such short range like the i3. If the speedo is that optimistic, is the odometer also off by a similar degree?