[mynameisnick4]

I recently switched to my winter wheels/tires that are 275/35/19 all around. This makes them slightly smaller on the rear thus a speedometer error. A fitment calculator has it at a +0.58% difference, so reading at 30.17MPH when going 30MPH and 60.35MPH when going 60MPH which is basically nothing.

Because I knew there may be a difference I started to pay attention to the speedometer vs GPS speed and noticed my speedo is always reading 2-3 MPH faster than the GPS speed. The wheel size change wouldn't account for this.

With all that said, these are my questions:

1. Is is typical for the speedometers to be off by this amount from factory?
   
2. Will this affect the odometer? I am assuming it would and add miles that weren't actually driven.
   
3. Can the speedometer be re-calibrated through coding or the dealer?
   
4. When you change your wheels in iDrive it actually allows you to select the size and choose 275/35/19. Does this setting change the speedometer calibration?

[JABCAT]

Stock BMWs always read 3 mph higher in the US. Both of my '22s do and I've been told it's normal. I just have to be aware when I drive my other vehicles that have accurate speedos.

[mynameisnick4]

Originally Posted by JABCAT

Stock BMWs always read 3 mph higher in the US. Both of my '22s do and I've been told it's normal. I just have to be aware when I drive my other vehicles that have accurate speedos.

Interesting, so it's just accepted that odometers are not accurate (if the odometer is calculated by vehicle speed)? As an example say you drive 10,000 miles a year and average 35MPH. If the speedo is reading high by 3MPH then that's around 850 extra miles a year you didn't drive.

[Tag]

My understanding is that it shows you a slightly faster speed to cover BMWs arse due to regulations on how accurate a spedo has to be. Even though they show you a slightly faster speed the odometer doesn't take that into account.

[JABCAT]

Originally Posted by mynameisnick4

Interesting, so it's just accepted that odometers are not accurate (if the odometer is calculated by vehicle speed)? As an example say you drive 10,000 miles a year and average 35MPH. If the speedo is reading high by 3MPH then that's around 850 extra miles a year you didn't drive.

I haven't noticed any discrepancy on the odometer, e.g., I know it's 1.5 miles to my kid's practice facility and the odometer registers 1.5 mi.

[RockCrusher]

Best I can tell both my 2023 JCW and my 2023 M2 speedos read 2mph high.

My experience over the years -- well starting in 2002 with my new Boxster -- is speedos can read high. My Boxster's speedo read 5mph high. I was concerned about this affecting the odometer. I did a distance test using a GPS device and over 200 miles -- accumulated in one non stop drive east to west across KS -- pretty flat and not many turns -- the GPS and car odometer differed by 0.2 of a mile. The car had a 50K mile warranty and that amounted to 50 miles error. Can't recall now if the error was in my favor or not.

My Cayman S and Turbo speedo errors were around 2mph. My GTO speedo was accurate. Other cars since then: MINI JCW, 3 Challengers, M-B cargo van, BMW 230i, MINI S; I don't recall what speedo errors -- if any -- they had.

While I haven't bothered to test the odometers of my JCW and M2 I believe they'll be unaffected by the speedo being optimistic.

[sacowich]

For me, 2mph difference between draggy/gps and G87 speedo.

[JABCAT]

I drove 229 miles this morning. Map/GPS said 229 mi & trip counter also said 229 miles. Both my '22 330e & X3MC are 3 mph high above 30 mph, 2 mph high below 30.

[mynameisnick4]

Originally Posted by JABCAT

I drove 229 miles this morning. Map/GPS said 229 mi & trip counter also said 229 miles. Both my '22 330e & X3MC are 3 mph high above 30 mph, 2 mph high below 30.

That's good to hear. I wonder what they use to calculate the odometer then.

[jhstjh]

Haven't tried on the M2 but on my previous BMW if plug an OBD2 reader and read the speed, it's actually slower than the one displayed on speedometer.

[RockCrusher]

Originally Posted by jhstjh

Haven't tried on the M2 but on my previous BMW if plug an OBD2 reader and read the speed, it's actually slower than the one displayed on speedometer.

Yes. I have used an OBD2 scan tool to monitor vehicle speed in real time and used it to confirm the vehicle speed agreed with GPS speed and in how much difference there was -- if any -- between speedo speed and OBD2/GPS speed.

[KC87ZB]

Yes, gone are the days when the speedometer and odometer use a geared system to display speed and distance, and the two were completely linked. When we transitioned to digital speed detection the speedo can be artificially set to read high, which most OEM's do.

That said, as far as I know, the speed and distance are calculated off the output shaft of the transmission, so if you change tire size you will impact speedo and odo. I could be wrong but I cannot imagine how else they would do it.

[Zatellia]

Originally Posted by JABCAT

Stock BMWs always read 3 mph higher in the US. Both of my '22s do and I've been told it's normal. I just have to be aware when I drive my other vehicles that have accurate speedos.

I was wondering that, when ever i pass a stationary radar that tell you your speed its always different then my speedo

[aerobod]

Originally Posted by KC87ZB

Yes, gone are the days when the speedometer and odometer use a geared system to display speed and distance, and the two were completely linked. When we transitioned to digital speed detection the speedo can be artificially set to read high, which most OEM's do.

That said, as far as I know, the speed and distance are calculated off the output shaft of the transmission, so if you change tire size you will impact speedo and odo. I could be wrong but I cannot imagine how else they would do it.

Not typically off the transmission output shaft since the advent of ABS and speedos switching from mechanical to electronic input many years ago. The ECU has input from all 4 wheels from the pulse generators near each hub, these signals are used for determining speed, distance and tyre slip, which is then processed as needed by various systems in the car.

[RockCrusher]

Originally Posted by Zatellia

I was wondering that, when ever i pass a stationary radar that tell you your speed its always different then my speedo

When I lived in Livermore CA there were several of the permanent and temporary speed radars around. I'd use them to see what the speedo error was for my various cars. (But I also had the benefit of a NAV unit which displayed speed and for further confidence I could and did connect an OBD2 scan tool.

Here in Benton County AR I only encountered one so far positioned just inside the AR/MO state line. I drove past it several times in both of my cars. (The radar was there for weeks...)

Oh, I forgot to mention but my experience in Livermore was occasionally there would be LEO (car or motorcycle) with a radar gun not too far past the stationary radar. It was not my thing to speed in town anyway so I was never that concerned. But I did have a V1 radar detector in one car and it not only alerted me to the stationary radar but also the cop beyond.