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      09-28-2014, 08:44 PM   #1
gago1101
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Speedometer reading - front or rear axle?

I am thinking of changing tire sizes and wondering how they will affect the speedo/miles. Does anyone know which axel is used to calculate milage and speed? is it the front or rear?
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      09-29-2014, 09:51 AM   #2
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I would say with almost certainty the rear axle.
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      09-30-2014, 05:05 PM   #3
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I guess you could always just floor it and spin the tires and see if your speedo goes up or just stays at zero.
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      09-30-2014, 08:00 PM   #4
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I'm guessing it takes it off the transmission (so effectively, the rear axle).
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      09-30-2014, 08:03 PM   #5
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I thought that the used a sensor on the diff.
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      10-03-2014, 02:12 PM   #6
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i've been told by bmw that the speedo indication shown is based on the computer's calculation of the vehicle's speed for the same purposes as traction control and stability control, meaning it draws information from all four wheels. how it makes that calculation, how it weighs changing parameters, and how it "corrects" are all a mystery to me. clearly it could be "fooled" with 4 tires of a similar increase or decrease in diameter, but it's harder to predict what will happen with a significant change to just one of the axles. supposedly the traction and stability systems will take issue with this, however i haven't experienced this myself in previous BMWs with all kinds of various tire combinations.
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