arosamond - I asked the same question a few posts ago. The logical answer would be yes you have to re-calibrate if you change the total of the wheel+tire sidewalls (total height).

A guy at work told me that in this day in new-age high tech electronics that wheel speed sensors automatically re-calculate this before sending the info to the speedometer. I think he may be full of it....Does anyone know if this is true or pure fantasy?

 

I was told that if you change the size that you do need to recalibrate, even on a newer car...

 

I don't see how the car would determine the new circumference of the aftermarket wheel/tire set. With larger wheels and tires, one complete revolution would cover more ground. I would think a recalibration of the speedo is in order.

 

Yeah, I thought so!

 

Just because you change to a larger wheel size (19" to 20" for example) does not mean the total circumstance of your wheel/tire combo will necessarily change.

Alot of times people who are running 20" wheels will have very, very low profile tires, which makes their total overall circumstance with the 20" approx. the same as with the 19".

Just my 0.02.