Quote:
Originally Posted by x7-AR
Here's the official do-nothing, take no responsibility reply from BMWUSA:
[COLOR="Navy"]Most speedometers have tolerances of approximately +10%. A "speedometer advance" is necessary to compensate for negative tolerances in tire diameter, electronic controls, tire temperature, tire pressure, vehicle load, and other factors. Vehicle manufacturers typically calibrate speedometers to read high by an amount equal to average error to ensure speedometers do not indicate a lower speed than the actual speed of the vehicle. The discrepancy you noted is within BMW specifications.[/COLOR]
So to summarize, BMW admits to a "speedometer advance" and suggests that it's ok because other companies do it and says it's necessary to compensate for changes in tire factors.
I'll skip the admission by BMW to "speedometer advance" since it appears I'm late to the party and everyone knows about BMW speedometer inflation. I'll also skip the lame excuse they gave that other companies do this so it's ok. What seems like BS to me is that this is even necessary. I would think the biggest factor regarding tires is wear. Since circumference is proportional to diameter, as your tires shrink in size, the car is actually going slower than the speedometer reads, not faster. The speedometer is going to report higher speeds over time as diameter changes with tire wear. Therefore, I would predict that if you have a 5% speedometer variance with a new car with new tires, that variance will get worse with tire wear and not close the gap ("compensate for negative" blah blah blah per BMWUSA).
If and when someone reads this that has more coding knowledge than me (read "any coding knowledge") and has a solution for the BMW intentional "speedometer advance" in my 2019 X7, please reach out.
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It's not a take no responsibility thing though. They have a responsibility to make sure their vehicles comply with all laws where they are sold. Laws usually dictate that speedometers absolutely cannot read slower than actual speed so BMW and other manufacturers add speed to compensate.
Here is more on it.
https://www.thrillist.com/cars/your-...-japanese-cars
Can you just use whichever app makes you happiest? Technically, GPS-based speed calculation will always be more accurate than wheel rotation based due to the changes in tire size over time. However, when testing this earlier today, it appeared Waze was polling every couple of seconds so it was lagging behind the X7 Speedometer changes. For instance I was completely stopped and Waze said 5mph. I set cruise to 60 and as soon as my speedometer hit 60 Waze was at 50, more than the tolerance. It soon normalized, but still it was lagged.
What resolution would make you happy? Coding is not hard as you suggested earlier, it just takes research/practice. You can also pay a 3rd party to code it. BMW will not do it since it is a legal liability for them.