BMW speedo off

"E90M3" (e90m3) 05/18/2016 at 10:06 • Filed to: None

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Anyone else with a BMW notice that the speed indicated by their speedo is more than what your GPS speed is? I’ve got an escort passport max, and it displays your GPS speed, and in the M3 it’s off about 3 mph and in the 128i it’s off 3-5 mph. It seems like this is intentional cause they know people drive their cars fast. Just wondering if anyone else has a similar experience with their BMW.

KatzManDu > E90M3 05/18/2016 at 10:08

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I’ve noticed it on both my E39 and my wife’s Mini.

Cé hé sin > E90M3 05/18/2016 at 10:11

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This is normal and applies to just about every car out there. The reason is speedos are allowed to over read, but not under read. To allow for inaccuracy they’re deliberately designed to over read by a couple of per cent.

If only EssExTee could be so grossly incandescent > E90M3 05/18/2016 at 10:11

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My 528i is off, and the faster you go the bigger the discrepancy gets. By the time you’re going 70, it’s indicating 75.

Tripper > E90M3 05/18/2016 at 10:12

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Speedo’s on German cars are notoriously boastful. Can confirm on E46 M3, E90M3, R53 Cooper, R56 Cooper, Audi S3

Aaron M - MasoFiST > E90M3 05/18/2016 at 10:12

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My 128i is no worse than my Subaru was, reading high by maybe 1-2mph.

E90M3 > If only EssExTee could be so grossly incandescent 05/18/2016 at 10:12

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same for both the M3 and the 128i, the faster the bigger the discrepancy.

E90M3 > Cé hé sin 05/18/2016 at 10:14

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My 1997 Ford Explorer was pretty much dead on, if it said you were going 45, you were going 45. Maybe that’s the difference between European and American cars, I’ve only had that explorer and my 2 BMWs, so I don’t have another point of reference.

RPM esq. > Tripper 05/18/2016 at 10:14

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It’s not just the Germans, it’s not just the sports cars, and it’s not to be boastful, it’s because they’d have to recall them if they under-indicated speed and so they err on the side of over-indicating.

Party-vi > E90M3 05/18/2016 at 10:14

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BMW speedos have always been a bit optimistic. The one in my E46 is pretty accurate though, according to my GPS speedo ap.

TheBloody, Oppositelock lives on in our shitposts. > E90M3 05/18/2016 at 10:14

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It’s pretty much the same with any vehicle, the speedo will always be about 3-5 mph off (normally showing faster speeds).

If only EssExTee could be so grossly incandescent > E90M3 05/18/2016 at 10:14

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Most cars have a similar issue but this is the worst I’ve ever seen it. My old Neon indicated 2-3mph LOWER than actual speed.

philipilihp > E90M3 05/18/2016 at 10:14

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I’ve noticed it in my E90 335i when going through one of those flashing “your speed is” signs in residential neighborhoods. The speed measured by the sign is usualy about 3mph slower than the speedo indicates.

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > E90M3 05/18/2016 at 10:15

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yup, can confirm. my dad’s e90 has this ‘feature’

Out, but with a W - has found the answer > E90M3 05/18/2016 at 10:18

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All car makers do this, since it’s impossible to make a 100% accurate speedo. This is because in general your speed is calculated based on the number of tire rotations in a certain amount of time. Since not every car from the same model line has the same tire size (compare a 320i with an M3), tire circumference will vary as well. Additionally, when your tires wear down, they become marginally smaller, leading to a higher indicated speed. All this (together with manufacturing tolerances) leads to margins on your speedo.

As to why they almost always indicate a higher speed: probably legal risks, i.e. so you don’t blame your inaccurate speedo and sue your car maker if you receive a speeding ticket.

Cé hé sin > E90M3 05/18/2016 at 10:18

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Chance! If you design the speedo to be +3% and the tolerance is +/- 3%...

RamblinRover Luxury-Yacht > Cé hé sin 05/18/2016 at 10:20

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...which, once you’ve gotten into insane miles and the gauge sticks a bit and has a fatigue-hardened spring, could be underreading anyway, in defiance of that... Strictly speaking of analog gauges, of course. There’s also the bit where a lot of gauges are possible to calibrate for different tires/etc. and thus can be made actually accurate.

TheRealBicycleBuck > E90M3 05/18/2016 at 10:22

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Don’t be certain that GPS-derived speedometers are accurate, especially at high speeds. GPS updates once per second. That is, the GPS satellites send a ping with the time, their current position, etc. once every second. The GPS receiver in your car receives this data and calculates your position. Your speed is calculated from this data. Normal errors in the data stream account for 3 to 100 meters of variability in your position. These can be error-corrected, but these require receivers that pick up the error correction signals for your general area. Changes in velocity between positional updates create additional error in the system. Some GPS units use accelerometers to provide additional data for the position calculation and that helps with accuracy, but no system is perfect.

I’ve had access to recreational and mapping-grade GPS equipment which I’ve used in many different vehicles. It isn’t unusual for the instruments to disagree with each other as well as the the speedometer. It’s funny to have two identical GPS units reporting different velocities while sitting side-by-side in the same truck.

BmanUltima's car still hasn't been fixed yet, he'll get on it tomorrow, honest. > E90M3 05/18/2016 at 10:23

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Yes, my E39 reads about 7 kph fast, no matter what speed you’re at. I’ve got a speed indicator on my GPS to compare with.

Junkrat aka Rick Sanchez: Fury Road Edition > E90M3 05/18/2016 at 10:29

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This is quite common. I know MkV VW’s speedo was off, and if you accessed a secret menu the radio would actually show the real mph. So the ECU knew your exact speed, but the speed is misrepresented on the actual speedometer. I would assume there are a few other cars out there like that.

JQJ213- Now With An Extra Cylinder! > E90M3 05/18/2016 at 10:30

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Does yours have optional or aftermarket wheels?

My C30s speedo was perfect with my stock 17" wheels. I upgraded to 18s and I’m not a few MPH off.

Reece-Current Stinger GT owner > E90M3 05/18/2016 at 10:36

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I’ve found this is pretty typical of BMW cars. My E46 reads about 2-3 fast and my MINI is the same exact way.

Dusty Ventures > Cé hé sin 05/18/2016 at 10:41

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Actually, I’ve tried all five of our American cars (two Lincolns, a Chrysler, and two Fords) and they’ve all been on the money. Our four Subarus have all read three mph fast.

HammerheadFistpunch > E90M3 05/18/2016 at 10:46

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Seems common enough, funny thing with the nox box (vw sportwagen tdi) is that the digital is accurate and the analog is fast

Dusty Ventures > Cé hé sin 05/18/2016 at 10:48

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Also every single Sprinter van I've driven for work (at least a dozen by now) has been dead accurate

d15b > TheRealBicycleBuck 05/18/2016 at 10:48

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Technical explanation! Nice.

d15b > Junkrat aka Rick Sanchez: Fury Road Edition 05/18/2016 at 10:49

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Really? What was the reason behind that?

Junkrat aka Rick Sanchez: Fury Road Edition > d15b 05/18/2016 at 11:50

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I have no idea. There were lots of threads on VWVortex, and probably still are. I remember some stories of fights with dealers/VW over getting it re-calibrated. I am pretty sure it can be fixed easily with the VAG tool.

nerd_racing > E90M3 05/18/2016 at 12:07

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My 128i does the exact same thing.

RPM esq. > E90M3 05/18/2016 at 12:11

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My BMW and my Audi both do this, but they do it differently: the BMW is sort of proportional, so that the amount by which it’s off goes up the faster you go; my Audi just reads 2-3 mph over no matter what—including if you’re creeping along at 1 mph, which is where it gets a little weird.

DynamicWeight > E90M3 05/18/2016 at 12:17

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When I was studying engineering in school, this actually becomes a big deal. See, all instruments are off. There is this huge word to learn: tolerance. Basically, it describes how much something can be off by. Measuring length, time and/or weight is all very easy until you want to start increasing your accuracy, and then it gets very hard (and expensive). For instance, if you want to calculate the speed of your car based of the rotations of your wheel, to get a very accurate result you would have to account for tread wear decreasing the diameter of the wheel over time!

In the case of speedometers, manufacturers always build them to look faster. This is for two reasons. One, liability, if someone was going faster than they thought they were and crash, they will blame the manufacturer. Two, it makes everything in the car look better. It will read back better MPGs, feel quieter at “faster” speeds. Seem to accelerate better etc. etc.

If I’ve got you at all interested here’s a couple fun facts: length, time, and weight are the basic measurements, all others are derived from these three. For instance, speed is length/time (ex. miles / hour). The first two, in the metric system, are based of physical constants in the universe. So, for instance, even if you lost every ruler in the world, you could still re-derive how big a meter is from measuring a physical phenomena. However, the third measurement, weight, is very interesting. There is no physical representation of weight. The kilogram is an arbitrary unit. There exists a specimen that has been declared to weigh exactly.... exactly one kilogram and that’s how everyone knows how much a kilogram weighs! If we ever lost it (and it’s seven sister specimens) we would have no way of accurately recreating it!

Stevo777 > E90M3 05/18/2016 at 13:04

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I think of it as a deterrent. I got pulled over once and the officer clocked me at 78mph, naturally I didn’t argue because my digital speedo stated I was doing 81mph (I had it on cruse control). Unless he was doing me a favor, but I kinda doubt it. This was prior to my radar detector days, haven’t gotten nailed since ;). Oh, and that officer let me go. Probably because I was close to home at 2am on a wednesday morning and I was the only car on the highway...

jmedarts > E90M3 05/18/2016 at 13:05

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I thought I read - on here probably - that the German government will hit the manufacturer with a very serious fine if the speedometer is displaying a speed that is slower than actual. In order to avoid this, they design them so that the “max tolerance” will never read slower than actual. That’s why german cars seem to be so uniform when it comes to this.

Eric @ opposite-lock.com > E90M3 05/18/2016 at 14:06

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I’ve only checked my daily drivers and they’re all American, more-or-less. The first two were dead on to slightly above actual speed when the tires were worn. The Lincoln is about 2 off on the high side (presumably the equivalent Jaguar was as well). The Focus is still dead on (but will probably be off when the tires wear down enough).

Jonathan Harper > E90M3 05/18/2016 at 15:10

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When I was shooting a lot of BMWs for an ad agency I would often use Waze while driving to locations, 90% of these brand new BMWs were 5mph off. Only the M3/M4s I drove seemed spot on.