In Reply to: BMW NA can get them recalibrated, but... posted by Bart B. on August 04, 2001 at 22:27:28:
...they're hard to convince to do it and it may be a waste of time anyway.
If you do get it recalibrated with a new set of tires, during the life of the tires the speedometer will be about 2% off as that's how much smaller the tire diameter/circumference will be.
Most cars's speedometers read a bit high anyway. It's no big thing to 99.9% of the drivers. The rest should get a portable GPS unit to read out actual speed to within 1/10th mph if they're an accuracy buff.