Speedometer accuracy

[scott10s]

Anybody else notice their speedometer reads 3 mph too high?

[MRCUR]

That's typical of every BMW I've ever driven.

[myzmak]

Originally Posted by MRCUR

That's typical of every BMW I've ever driven.

....and of speedometers in general

Most speedometers have tolerances of some ±10%, mainly due to variations in tire diameter. Sources of error due to tire diameter variations are wear, temperature, pressure, vehicle load, and nominal tire size. Vehicle manufacturers usually calibrate speedometers to read high by an amount equal to the average error, to ensure that their speedometers never indicate a lower speed than the actual speed of the vehicle, to ensure they are not liable for drivers violating speed limits.

http://en.wikipedia.org/wiki/Speedometer#Error

I recall a lengthy discussion on this around 9 months ago in relation to the 'true top speed' of this car (it will display higher than it is actually going....)

will see if I can find it.

edit: yeah, here:

http://f80.bimmerpost.com/forums/sho...71&postcount=6

BMWs can display up to 10% + 2.4 mph over the actual speed

(the example being at 50 mph of actual speed, the display can be as high as 57.4 ((50 mph x 10%) + 2.4 mph)

(props to M6-Coupe coupe for the post)

[shortseller]

There was a formula around here sometime ago, official BMW calculation, maybe someone can post. And yes, we do run lower than speedometer readout, to which I will admit, it has saved my ass atleast once since getting the car.

[SierraZulu9]

BMW's are usually about 3 mph slower than indicated at highway speeds. Once you get on the track and are hitting 150+ the difference between your indicated and higher speed gets even higher.

[shortseller]

I believe this can be corrected by coding to be accurate. 10% + 2.4mph seems a piece off the mark.

[NorCal f80]

Originally Posted by shortseller

I believe this can be corrected by coding to be accurate. 10% + 2.4mph seems a piece off the mark.

I hope this is true. I hate how I see 86mph on my HUD but I'm right next to everyone else.

[X2Board]

Originally Posted by 0-100 ninja real quick

I hope this is true. I hate how I see 86mph on my HUD but I'm right next to everyone else.

That's mostly because no one wants to get passed by a BMW.

[fortressmaximus]

Originally Posted by M Drei Fahrer

That's mostly because no one wants to get passed by a BMW.

Haha

[myzmak]

Originally Posted by shortseller

I believe this can be corrected by coding to be accurate. 10% + 2.4mph seems a piece off the mark.

Originally Posted by 0-100 ninja real quick

I hope this is true. I hate how I see 86mph on my HUD but I'm right next to everyone else.

I dont know if it can be, but it makes sense to me that it errs like this.

Far better for someone to be going a little less fast than they think than to be inadvertently speeding. (as such, from what i can see, in every country the number 1 rule is: speedometer can never, ever show less than the actual speed)

Is this too great a margin? I dunno. Maybe.....but it is hard to pick a 'better number' out of the air.

The wikipedia article i linked to above indicates that in the US of A the max for commercial vehicles is 5mph at 50mph (though not, by omission, for non-commercial vehicles)

[jim101]

Originally Posted by scott10s

Anybody else notice their speedometer reads 3 mph too high?

Yes.

[schnell325]

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