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Originally Posted by 2007/335i/coupe
So I finally got a chance to use the cruise control feature on my car and noticed that the white tick and the speedometer reading is about 5 miles off at 60mph. I have the sport package on my car with the 18" wheels, is this causing the incorrect reading my on speedometer? Anyone else experiencing this or is there some kind of malfunction.
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Are you saying that the white tick and the speedometer needle aren't pointing to each other? I don't think the size of your wheels would cause that. Both the cruise control and the speedometer use the same sensors to determine the rotation of at least one wheel so they're determining your speed based on that. If you put on 17" wheels the speedometer will show the same speed as before even when the wheel rpms are the same but since the tires have a different circumference, the car may show you're bookin' along at 65 mph when you actually poking along at 58 mph (OK, more realistic -- 85 vs. 78).
Now if the cruise control is calibrated differently than the speedometer, i.e., expecting each rotation of the wheel to represent a factor of X while the speedometer uses a factor of Y then, yes, your gauges wouldn't match. What I mean by this is, one gauge is expecting 17" wheels and the other is expecting 18" wheels. I suspect that this can easily be rectified with a software setting and not, as in older cars with mechanical speedometers, a gearing change.
What the actual purpose of the tick is, I do not know. To me it's pretty useless since it drops off anytime the cruise control is disengaged.