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If my speedometer is off, is my odometer wrong, too?

My 530e speedometer registers 3 miles an hour faster than the car is actually traveling, at either 30 mph or 70 mph. Doesn’t that mean that the odometer is logging more miles than I’m travelling? Would putting larger diameter tires on the car fix this?

Most vehicles indicate a speed that is higher than actual so you will not get ticket. That said some even show a lower speed that actual because they are not NASA grade instruments . I don’t put this in the big worry category.

Edit: 73 MPH by 0.96 = 70.08 MPH - 100000 miles by 0.96 = 96000 miles . You will not be going at 70 all the time so you are worrying about a non -issue.

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No need to guess. There are usually mile interval road markers on most freeways, mile after mile, so you can check both your odometer and mph using those. At 60 mph you should pass those markers at exactly 60 second intervals. Look for little posts stuck in the ground. They usually have numbers on them, and are used by the road crews and police. For example the road crew might be instructed to fix a pothole 200 feet south of the 16 mile marker. It used to be the case that the odometer was linked to the mph needle mechanically, but that might not be the case anymore. Depends on the car.